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Separation of caffeine and theophylline in poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection
Abstract
A method for the rapid separation and sensitive determination of caffeine and theophylline was presented in poly(dimethylsiloxane) (PDMS) microchannel electrophoresis integrated with electrochemical detection. By using methanol as an additive, the peak shape and resolution were essentially improved. The analytes were well separated within only 40s in the running buffer of 5.0mM borate solution (pH 9.2) containing 10% (v/v) methanol. The linear ranges were from 6microM to 0.6mM and the detection limits were 4microM for caffeine and theophylline, respectively. The proposed method has been successfully applied to determine caffeine and theophylline in rat serum and urine.
... Electrochemical methods offer distinct advantages over these analytical methods, which include: fast, precise, portable and affordable methods/devices whilst also offering high sensitivity and selectivity towards electroactive analytes. [13] Hyphenated techniques have been utilised for the detection of theophylline [14][15][16][17] and overcome the potential disadvantage, in some cases, of electrochemical approaches, where in complex samples, selectivity might be an issue when compared to traditional laboratory based analytical techniques. Zhang et al. [17] reported theophylline and caffeine determination using a poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection using a carbon fiber microdisk electrode (diameter of 8 μm). ...
... [13] Hyphenated techniques have been utilised for the detection of theophylline [14][15][16][17] and overcome the potential disadvantage, in some cases, of electrochemical approaches, where in complex samples, selectivity might be an issue when compared to traditional laboratory based analytical techniques. Zhang et al. [17] reported theophylline and caffeine determination using a poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection using a carbon fiber microdisk electrode (diameter of 8 μm). A linear range from 6 μM to 0.6 mM was shown to be possible for both theophylline and caffeine with detection limits of 4 μM. ...
... This analytical methodology was successfully applied to determine caffeine and theophylline in rat serum and urine, which was found to agree with individual HPLC analysis. This analytical approach, as stated by the authors has advantages such as: cheapness, simplification, good resolution, and low reagent consumption [17]. Augustijns and Verbeke described the use of HPLC with electrochemical detection (HPLC-ECD), using a double electrode configuration method for the sensing of theophylline which exhibited a linear range from 2.5 to 20 pg/mL with a limit of detection (LOD) of 0.2 pg/mL. ...
In this overview, we explore the electroanalytical determination of theophylline. Theophylline finds use as a bronchodilator for treating diseases such as asthma and chronic obstructive pulmonary disease (COPD). There is a need to measure the concentration of theophylline in pharmaceuticals for QA/QC purposes as well as in plasma samples to ensure the doses of theophylline are at the correct therapeutic levels. If the concentration levels of theophylline deviate from the therapeutic levels (10 – 20 µg/mL for asthma), then patients can experience adverse effects. As such, there is a desire to progress from traditional lab based techniques to portable rapid testing. In this overview, we review the endeavours directed to the development of theophylline electroanalytical sensors, noting current and future trends.
... The effects of caffeine on humans depends on concentrations consumed. Consumption of high concentration of this compound causes various physiological and psychological effects such as relaxation of bronchial muscle, stimulation of the central nervous system, gastric acid secretion and dieresis (Zhang et al., 2005;Minamisawa, 2004;Yukawa et al., 2004;Bolton and Null, 1981). Increases in concentration of caffeine in vivo are also a key marker for various disorders, including heart disease, kidney malfunction and asthma. ...
... Moreover our sleeping habit, performance, and concentration are modified by caffeine ( Zhang et al., 2005;Najafi et al., 2003;Singh and Sahu, 2000;Bolton and Null, 1981). Caffeine is rapidly and completely absorbed from gastrointestinal tract with in a short period of time from consumption and then distributed through out the body (Clarke and Macarae, 1985). ...
... Due to above mentioned facts many chemical and physical methods have been developed The spectrophotometric method is fast, simple, accurate, reproducible and inexpensive procedure as compared to other methods, but it is not possible to determine caffeine directly in coffee beans by conventional UV-Vis absorption measurement due to the spectral overlap of UV absorbing substances in the sample (Belay, 2010;Belay et al., 2008;Zhang et al., 2005 ). Derivative spectrophotometry is relatively easy, but; it is not reliable for the small concentration of caffeine in samples. ...
In this research the methods of measuring major bioactive compounds in coffee beans,
their optical transition properties, self-association, hetero-association and thermodynamic
properties were investigated by experimental and computational methods. The implemented
methods for determination the contents of biocactive compounds in coffee beans
are the extraction of caffeine from water solution or liquid-liquid extraction and fitting
Gaussian function to the spectrum of the compound by non-linear curve fitting based on
the Lavenberg-Marquardt algorithm to eliminate the possible interferences. The contents
of caffeine and chlorogenic acids determined by these methods for green coffee beans
are in the ranges of 0.90-1.27 %, 6.05-6.25 % respectively. The optical transition properties
of caffeine, caffeic and 5-caffeoylquinic acids were determined in different solvents by
integrating the absorption coefficients in the wave number regions. The calculated values
of transition dipole moment of caffeine, caffeic and 5-caffeoylquinic acids in water in
their wave number regions are 10.40×10−30, 19×10−30, 20×10−30Cm respectively. The corresponding
oscillator strength are 0.19, 0.49 and 0.56. The concentration dependent selfassociation
of caffeic, 5-caffeoylquinic acids and their hetero-association were analyzed
by dimer model and Benesi-Hildebrand approaches. The thermodynamic parameters, enthalpy,
Gibbs free energy and entropy of dimerzation reactions were calculated from Van’t
Hoff equation. The calculated molar enthalpy change for caffeic and 5-caffeoylquinic acids
of self-association are -63.20, -12.89 kJmol−1 respectively.In addition, the time dependent
Schrodinger equations were solved by semi-classical approach to relate the theoretical expressions
with the experimentally measurable quantities.
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... It causes various physiological effects such as relaxation of bronchial muscle, stimulation of the central nervous system, gastric acid secretion and dieresis Bolton and Null (1981). And their concentration in vivo is a key mark for various disorders including heart disease, carcinogenesis, kidney malfunction and asthma (Zhang, Lian, Wang, & Chen, 2005). On the other hand, chemical analysis of caffeine in coffee beans is also used as an additional tool for evaluating coffee quality. ...
... Several chemical and physical methods have been developed for the determination of caffeine in coffee and other beverages. The most widely used methods for the determination of caffeine in beverages include various analytical techniques such as derivative spectrophotometer (Alpdogan, Karbina, & Sungur, 2002) HPLC (Branstrom & Edenteg, 2002;Casal, Oliveira, & Ferreira, 2000;Minawlsawa, Yoshida, & Takali, 2004;Ortega-Burrales, Padilla-Weigand, & Molina-Diaz, 2002), Fourier Transform infrared (Bousain, Garriques, Garriges, & Guardia, 1999;Najafi, Hamid, & Afshin, 2003;Paradkar & Irudayaraj, 2002), NIR reflectance spectrometry (Chen, Zhao, Huang, Zhang, & Liu, 2006), Raman spectroscopy (Edawards, Munish, & Anstis, 2005) and capillary electrophoresis (Zhang et al., 2005), which have been reported. Although Spectrophotometer is a fast and simple method it is not possible to determine caffeine directly in coffee beans by conventional UV absorption measurement due to the spectral overlap (Zhang et al., 2005). ...
... The most widely used methods for the determination of caffeine in beverages include various analytical techniques such as derivative spectrophotometer (Alpdogan, Karbina, & Sungur, 2002) HPLC (Branstrom & Edenteg, 2002;Casal, Oliveira, & Ferreira, 2000;Minawlsawa, Yoshida, & Takali, 2004;Ortega-Burrales, Padilla-Weigand, & Molina-Diaz, 2002), Fourier Transform infrared (Bousain, Garriques, Garriges, & Guardia, 1999;Najafi, Hamid, & Afshin, 2003;Paradkar & Irudayaraj, 2002), NIR reflectance spectrometry (Chen, Zhao, Huang, Zhang, & Liu, 2006), Raman spectroscopy (Edawards, Munish, & Anstis, 2005) and capillary electrophoresis (Zhang et al., 2005), which have been reported. Although Spectrophotometer is a fast and simple method it is not possible to determine caffeine directly in coffee beans by conventional UV absorption measurement due to the spectral overlap (Zhang et al., 2005). On the other hand, the derivative spectrophotometer is relatively easy; however, it is not reliable for the determination of small concentration of caffeine in samples. ...
... The effects of caffeine on human being depend on concentrations. Consuming high concentration of this compound causes various physiological and psychological effects such as relaxation of bronchial muscle, stimulation of the central nervous system, gastric acid secretion and diuresis (Zhang et al., 2005;Minamisawa, 2004;Yukawa, 2004;Bolton and Null, 1981). The increases in concentration of caffeine in vivo are also a key mark for various disorder including heart disease, kidney malfunction and asthma. ...
... The increases in concentration of caffeine in vivo are also a key mark for various disorder including heart disease, kidney malfunction and asthma. Moreover, our sleeping habit, performance, and concentration are modified by caffeine (Zhang et al., 2005;Najafi et al., 2003;Singh and Sahu, 2000;Bolton and Null, 1981). Caffeine has a tendency of rapidly and completely absorbed from gastrointestinal tract within a short period of time and distributed in the body (Kervigan and Lindsey, 2005;Clarke and Macarae, 1985); however, it is not removed from the circulation until metabolized initially into paraxanthine, thephylline and thyobromine then into derivative of uric acid and diaminourcil, which is eventually removed from the circulation. ...
... Due to aforementioned facts, many chemical and physical methods have been developed for the determination of caffeine in coffee and other beverages. The most widely used methods for the determination of caffeine in beverages are UV-Vis spectrophotometer and partial least square (L-Martinez, 2003; Oztem et al., 2003), UV-Vis spectrophotometer (Singh and Sahu, 2006;Belay et al., 2008;Belay, 2010), luminescscence (Wei et al., 2005;Masatoki and Hirokazu, 1989;Andino et al., 1987), derivative spectrophotometer (Alpdogan et al., 2002;Lau et al., 1992), HPLC (Mumin et al., 2006;Aragao et al., 2005;Minamisawa, 2004;Levent, 2002;Qi et al., 2002;Ortega-Burrales et al., 2002;Casal et al., 2000), Fourier transform infrared spectroscopy (NajafI et al., 2003;Paradkar and Irudayaraj, 2002;Bousain et al., 1999), near infrared reflectance (NIR Reflectance) spectrometry (Chen et al., 2006;Huck et al., 2005;Rodriquez-Saona et al., 2005), Raman spectroscopy (Edawards et al., 2005) and capillary electrophoresis (Zhang et al., 2005) are very commonly used techniques. ...
The chemical characteristics, composition, and the physiological and psychological effects of caffeine and chlorogenic acids in biological systems are presented, along with their relationships with coffee quality. In addition, various chemical and physical methods that can be used for the routine analysis of the contents of these compounds in coffee beans are reviewed.
... The effects of caffeine on human being depend on concentrations. Consuming high concentration of this compound causes various physiological and psychological effects such as relaxation of bronchial muscle, stimulation of the central nervous system, gastric acid secretion and diuresis (Zhang et al., 2005;Minamisawa, 2004;Yukawa, 2004;Bolton and Null, 1981). The increases in concentration of caffeine in vivo are also a key mark for various disorder including heart disease, kidney malfunction and asthma. ...
... The increases in concentration of caffeine in vivo are also a key mark for various disorder including heart disease, kidney malfunction and asthma. Moreover, our sleeping habit, performance, and concentration are modified by caffeine (Zhang et al., 2005;Najafi et al., 2003;Singh and Sahu, 2000;Bolton and Null, 1981). Caffeine has a tendency of rapidly and completely absorbed from gastrointestinal tract within a short period of time and distributed in the body (Kervigan and Lindsey, 2005;Clarke and Macarae, 1985); however, it is not removed from the circulation until metabolized initially into paraxanthine, thephylline and thyobromine then into derivative of uric acid and diaminourcil, which is eventually removed from the circulation. ...
... Due to aforementioned facts, many chemical and physical methods have been developed for the determination of caffeine in coffee and other beverages. The most widely used methods for the determination of caffeine in beverages are UV-Vis spectrophotometer and partial least square (L-Martinez, 2003; Oztem et al., 2003), UV-Vis spectrophotometer (Singh and Sahu, 2006;Belay et al., 2008;Belay, 2010), luminescscence (Wei et al., 2005;Masatoki and Hirokazu, 1989;Andino et al., 1987), derivative spectrophotometer (Alpdogan et al., 2002;Lau et al., 1992), HPLC (Mumin et al., 2006;Aragao et al., 2005;Minamisawa, 2004;Levent, 2002;Qi et al., 2002;Ortega-Burrales et al., 2002;Casal et al., 2000), Fourier transform infrared spectroscopy (NajafI et al., 2003;Paradkar and Irudayaraj, 2002;Bousain et al., 1999), near infrared reflectance (NIR Reflectance) spectrometry (Chen et al., 2006;Huck et al., 2005;Rodriquez-Saona et al., 2005), Raman spectroscopy (Edawards et al., 2005) and capillary electrophoresis (Zhang et al., 2005) are very commonly used techniques. ...
In this paper, the literature review related to the chemical characteristics, composition and the various physiological and psychological effects of caffeine, chlorogenic acids in biological system and their relation with coffee quality have been presented. In addition, the contents of these biologically active compounds in coffee beans, the different chemical and physical methods used to analyze these compounds in coffee beans were reviewed.
... In addition, CAF or CGA should be extracted from coffee solution before measurement. These can be performed by extraction and isolation of CAF and CGA using organic solvents like benzene, chloroform, and dichloromethane (Zhang, Lian, Wang, & Chen, 2005), which are harmful for health and environment. ...
... Directly determination of CGA in coffee is impossible due to UVabsorbing matrix (Belay & Gholap, 2009;Zhang et al., 2005). In order to eliminate this difficulty, background correction was used. ...
Abstract
In this research, the application of the first order derivative spectra was employed to determine the levels of caffeine (CAF) and chlorogenic acids (CGA) in defective (immature, black, and sour) and non-defective coffee beans without using extraction or background correction techniques. The extreme points of first order derivate spectra of these compounds were at the wavelength of 260 nm and 292 nm enable to quantify the contents of caffeine and chlorogenic acids respectively. The level of caffeine and chlorogenic acids in coffee beans determined by this method is ranged from 1.2 ± 0.12 - 1.46 ± 0.47% and 4.04 ± 0.44 - 4.43 ± 0.43% respectively. The study results also indicated total contents of caffeine and chlorogenic acids levels discriminate the defective and non-defective coffee beans with higher caffeine and chlorogenic acids contents being observed in defective coffee beans. As the method, it is extremely rapid, easy, and inexpensive and also requires minimal sample preparation for the quantification of caffeine and chlorogenic acids contents in coffee, it could be a valuable quality control technique.
... This method presents various advantages: it is sensitive, cheap, and easy regarding both the measurement procedure and the data analysis. The proposed protocol may allow replacing the use of expensive equipment, such as those required to apply standard High Performance Liquid Chromatography (HPLC) methods that at the moment limit the application in small industrial laboratories where a few analyses are performed each day [28][29][30]. The method here described could be applied to different states of coffee, such as beans, grounds coffee, coffee espresso, or brew, and to different food matrices having caffeine or CGAs as ingredients. ...
... The optical activity in this spectral range could be associated with → * electronic transition of caffeine, chlorogenic acids, and trigonelline molecules [18]. Usually, the spectral interference between the caffeine absorbance and other UV absorption signals due to the other substances in the sample had been dissuaded from the use of UV/Vis spectroscopy to obtain a correct determination of caffeine or chlorogenic acids content in coffee [30,37]. However, some methods aiming to use this technique were proposed [32,35], but they need an early chemical separation of the substances having an absorbance in the same spectral range or a specialist chemometric analysis of the data. ...
A simple method for the simultaneous determination of caffeine and chlorogenic acids content in green coffee was reported. The method was based on the use of UV/Vis absorption. It is relevant that the quantification of both caffeine and chlorogenic acids was performed without their preliminary chemical separation despite their spectral overlap in the range 250–350 nm. Green coffee was extracted with 70% ethanol aqueous solution; then the solution was analyzed by spectroscopy. Quantitative determination was obtained analytically through deconvolution of the absorption spectrum and by applying the Lambert-Beer law. The bands used for the deconvolution were the absorption bands of both caffeine and chlorogenic acids standards. The molar extinction coefficients for caffeine and chlorogenic acid in ethanol solution at 70% were calculated by using the chemical standards; the estimated values were ε(272 nm)=12159±97 M ⁻¹ cm ⁻¹ for caffeine and ε(330 nm)=27025±190 M ⁻¹ cm ⁻¹ for chlorogenic acids molecules, respectively. The estimate of concentration values was in agreement with the one obtained by High Performance Liquid Chromatography quantification. The method is fast and simple and allows us to realize routine controls during the coffee production. In addition, it could be applied on roasted coffee and espresso coffee.
... Drug testing by micro-analytical devices provides low-cost, reliable, and rapid results, with varied applications ranging from clinical diagnostics to forensic investigation to pharmaceuticals. 167 Of great concern, drug abuse and the over-prescription of drugs-particularly narcotics and stimulants, such as amphetamines, methamphetamines, codeine, and morphine-may have serious physiological effects on the drug user. Such inadvertent effects may include excessive nervous system stimulus, hindered breathing due to relaxed bronchial muscle, and the secretion of gastric acid, in addition to several other toxic and dangerous symptoms. ...
... Such inadvertent effects may include excessive nervous system stimulus, hindered breathing due to relaxed bronchial muscle, and the secretion of gastric acid, in addition to several other toxic and dangerous symptoms. [167][168][169][170][171][172] On top of these physical and biological side effects, social issues may develop due to the drug abuse and overuse, increasing the demand for facile drug testing. This need may be addressed using paper-based devices in the coming years. ...
A transformation of the healthcare industry is necessary and imminent: hospital-centered, reactive care will soon give way to proactive, person-centered care which focuses on individuals' well-being. However, this transition will only be made possible through scientific innovation. Next-generation technologies will be the key to developing affordable and accessible care, while also lowering the costs of healthcare. A promising solution to this challenge is low-cost continuous health monitoring; this approach allows for effective screening, analysis, and diagnosis and facilitates proactive medical intervention. Urine has great promise for being a key resource for health monitoring; unlike blood, it can be collected effortlessly on a daily basis without pain or the need for special equipment. Unfortunately, the commercial rapid urine analysis tests that exist today can only go so far—this is where the promise of microfluidic devices lies. Microfluidic devices have a proven record of being effective analytical devices, capable of controlling the flow of fluid samples, containing reaction and detection zones, and displaying results, all within a compact footprint. Moving past traditional glass- and polymer-based microfluidics, paper-based microfluidic devices possess the same diagnostic ability, with the added benefits of facile manufacturing, low-cost implementation, and disposability. Hence, we review the recent progress in the application of paper-based microfluidics to urine analysis as a solution to providing continuous health monitoring for proactive care. First, we present important considerations for point-of-care diagnostic devices. We then discuss what urine is and how paper functions as the substrate for urine analysis. Next, we cover the current commercial rapid tests that exist and thereby demonstrate where paper-based microfluidic urine analysis devices may fit into the commercial market in the future. Afterward, we discuss various fabrication techniques that have been recently developed for paper-based microfluidic devices. Transitioning from fabrication to implementation, we present some of the clinically implemented urine assays and their importance in healthcare and clinical diagnosis, with a focus on paper-based microfluidic assays. We then conclude by providing an overview of select biomarker research tailored towards urine diagnostics. This review will demonstrate the applicability of paper-based assays for urine analysis and where they may fit into the commercial healthcare market.
... Genetic and environmental factors are the major causes of variations of caffeine content in the coffee beans. Different levels of caffeine content in the coffee bean cause various physiological and psychological effects in humans [45][46][47]. About 80% of administered caffeine (1,3,7-trimethylxanthine) is metabolized by demethylation to paraxanthine (1,7-dimethylxanthine) via liver cytochrome P-450 1A2, and about 16% is converted to theobromine and theophylline, (3,7-and 1,3-dimethylxanthine, respectively) [47]. ...
Coffee as a cash crop, reduces food insecurity by providing regular incomes and is a major foreign exchange earner in more than fifty tropical countries where it is grown either as Arabica (Coffea arabica) or Robust (Coffea canepora). In Kenya which grow some Robusta but mostly Arabica coffee, the production has been declining, mainly because world coffee prices have plummeted to about 5 USD for a 650Kg of un-hulled beans per acre. The only way world prices are likely to increase and benefit the small-scale farmers, is by improving the cup quality and enabling these countries to sell their coffee in specialty markets. This review, underscores the importance of analyzing and estimating organoleptic, sensory and biochemical compounds diversity in Arabica coffee, since these are the factors that determine cup quality. In an attempt to do so, the chapter presents experimental data that analyzed various sensory and organoleptic traits of Arabica coffee and their Arabusta hybrids that proves that tremendous genetic diversity exists in coffee genotypes grown in Kenya and it is possible to utilize this genetic variation to improve cup quality.
... And their concentration in vivo is a key mark for various disorders including heart disease, carcinogenesis, kidney malfunction and asthma [8]. Therefore, establishing a rapid and cheap analytical method for the determination of caffeine in foods and drinks has an interest for a wide range of physiological effects on the human body and quality controls [9]. ...
In this work a study was performed using UV/Vis spectrophotometer to determine the concentrations of caffeine in coffee, tea and chocolate milk available in local market in Riyadh, Saudi Arabia. Quantitative analysis was carried using dichloromethane as extracting solvent. Results showed that the minimum caffeine level was observed in the chocolate milk (16.38 ppm) and the highest caffeine content observes in coffee (32 ppm).
... Moreover, caffeine is one of the important components of coffee beans which used to characterize the quality of coffee. Caffeine is a xanthine derivative known to stimulate the central nervous system and causes various physiological effects like the relaxation of the bronchial muscle, gastric acid secretion and dieresis [17,18]. However, high dose may produce negative effects in some sensitive individuals such as anxiety, tachycardia, restlessness, excitement, and insomnia [19,20,21]. ...
Coffee is one of the most popular drinks in the world. The quality of coffee depends on post harvesting process, agricultural practices, agro ecology conditions and chemical composition of coffee beans. Hararghe is among the major coffee producing areas in Ethiopia. However, the chemical profiles of Hararghe coffee beans have never been reported. The objectives of the present study was to determine pH value, total acidity and total polyphenols of Hararghe green coffee beans and also evaluates the effect of roasting temperature on caffeine content. Fifteen coffee bean samples were collected from different areas of Hararghe, Ethiopia. Total polyphenols were determined using the Folin-Ciocalteu reagent. The pH value was measured by a pH meter. The total acidities were determined by titrating with NaOH. The caffeine content from roasted coffee beans was measured using a UV-Vis spectroscopy. The lowest (5.26) and the highest (5.66) pH values showed by the coffee bean samples collected from Jarso and Gurachae, respectively. On the contrary, the lowest (1.44 ml of NaOHg-1) and highest (2.3 NaOHg-1) total acidity values revealed by Gurache and Jarso coffee green beans, respectively. Likewise, the lowest and the highest total polyphenols content exhibited by Girawa (7.22 mg GAE/g) and Kobo (20.96 mg GAE/g) coffee beans, respectively. The caffeine content in coffee bean samples roasted at different temperatures varied from 2.36 (w/w %) to 6.09 (w/w %). The content of caffeine increased from low temperature - long ranged time roasted coffee beans to intermediate temperature - intermediate ranged time. However, it was gradually decreased from intermediate temperature - intermediate ranged time to high temperature - short ranged time.
... In this project, it was intended to determine caffeine levels of coffee samples obtained from selected (major coffee producing) areas of Bale zone, and also to see differences (if any) between caffeine contents of forest and cultivated coffee beans. To do so, HPLC method was employed [51]. ...
Ethiopia is the home land of biodiversity of coffea arabica seeds. The major and most known coffee producing regions in the country are Oromiya and Southern Nations Nationalities and Peoples Region. The objective of this study was to determine the caffeine content of coffee bean samples obtained from coffee growing areasof Bale zone, Oromia region. The samples were collected from farmers' union that supplies coffee to Ethiopian Commodity Exchange (ECX) or exporters. The collected samples were roasted and powdered to facilitate the extraction. The powders were then boiled with water, filtered and subjected to liquid-liquid extraction using dichloromethane. The extracts were subjected to High Performance Liquid Chromatographic analysis. The results revealed that caffeine levels to be 1.31 ± 0.14% for Gololcha coffee, 1.32 ± 0.03% for Harena Buluk forest coffee, 1.33 ± 0.08% for Mena forest coffee, 1.34 ± 0.21% for Berbere coffee, 1.36 ± 0.02% for Harena Buluk cultivated coffee and 1.36 ± 0.16% for Mena cultivated coffee (on dry matter basis). The finding also showed that there are no significant differences in the caffeine contents of the coffee samples used in the study. Moreover, the caffeine contents were in the range of export standards of Ethiopia.
... This system exhibited good reproducibility and a high correlation with the conventional spectrophotometric method. The integration of microfluidic devices with different approaches, including electrophoresis, optics, and immunoassays, was successfully used for detecting drugs and metabolites in urine samples [30,31]. Caffeine and theophylline could be effectively separated using the microchannel electrophoresis integrated with electrochemical detection, and illicit drugs were detected with a high accuracy using the microfluidic device with an ultraviolet detection function. ...
Microfluidics is considered an important technology that is suitable for numerous biomedical applications, including cancer diagnosis, metastasis, drug delivery, and tissue engineering. Although microfluidics is still considered to be a new approach in urological research, several pioneering studies have been reported in recent years. In this paper, we reviewed urological research works using microfluidic devices. Microfluidic devices were used for the detection of prostate and bladder cancer and the characterization of cancer microenvironments. The potential applications of microfluidics in urinary analysis and sperm sorting were demonstrated. The use of microfluidic devices in urology research can provide high-throughput, high-precision, and low-cost analyzing platforms.
... Furthermore, it gives relief from the depression and discomfort associated with alcohol consumption and also serves as a drug for the treatment of arterial hypotension [2]. But, the high level intake of caffeine results many pharmacological effects such as diuretic, gastric acid secretion and stimulant of central nervous system [3,4]. A recommended dose of caffeine is 200-500 mg to the adult for a mild stimulation. ...
The authors report on the fabrication of Co(OH)2-enfolded Cu2O nanocubes on reduced graphene oxide (rGO), and the use of this material in an electrochemical caffeine sensor. The rGO/Cu2O/Co(OH)2 composite was characterized by X-ray powder diffraction pattern analysis, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. A rotating disc glassy carbon electrode covered with the nanocomposite displays enhanced electrocatalytic activity towards the electro-oxidation of caffeine. The peak oxidation potential is at 1.4 V (vs. Ag/AgCl) and hence is strongly shifted to the negative side when compared to other modified electrodes. The calibration plot is linear in the 0.83 to 1200 μM concentration range, with a 0.4 μM detection limit (at a signal-to-noise ratio of 3). The modified electrode is sensitive, selective and stable. It was successfully applied to the determination of caffeine in (spiked) caffeine-containing beverages and coffee powder and gave recoveries that ranged from 95.7 to 98.3 %.
Graphical abstract
Co(OH)2 enfolded Cu2O nanocubes on reduced graphene oxide (rGO) for the caffeine sensor
... ASA and another pharmaceutical product, caffeine (CF) are usually found together in most formulation tablets. CF is used as a stimulant to reduce physical exhaustion and to restore alertness due to drowsiness [7,8] . These pharmaceutical products are known to have several physiological effects such as gastric acid secretion and dieresis [9] . ...
A highly sensitive voltammetric sensor for aspirin (ASA) and caffeine (CF) was fabricated on a glassy carbon electrode (GCE) modified with a composite film of poly (4–vinylpyridine) (P4VP) and multiwall carbon nanotubes (MWCNT). Cyclic voltammetry of P4VP–MWCNT/GCE indicated that the electrode reaction was a typical diffusion limiting process and the catalytic reaction of ASA and CF was observed in 0.1 M phosphate buffer (pH 7.4). For the detection of ASA, a 30 fold improvement was observed in the anodic peak current _I_pa, at P4VP–MWCNT/GCE compared to the bare GCE. At the optimum parameter, _I_pa was found to be linearly dependent on the concentrations of ASA (0.04–350 µM) and CF (2.0–200 µM). The detection limits were 4.42 nM and 1.19 nM for ASA and CF respectively. The differential pulse voltammetry determination of ASA and CF in the presence of paracetamol (PCT) showed that ASA could be assayed in biological samples free from the interference of CF and PCT. The fabricated P4VP–MWCNT/GCE also displayed good stability, reproducibility and recovery in pharmaceutical and biological samples.
... However, the result of sensitivity was not satisfied within some methods, including CE [15,16], HPTLC [17] and spectrophotometry [18,19]. Additionally, some methods with high sensitivity only focus on one drug and or its metabolites, such as GC [20,21], electrochemical analysis [22,23], as well as HPLC and MS techniques [24][25][26][27], and to our knowledge, no method was used to detect simultaneously both promethazine hydrochloride and caffeine as well as their metabolites. Considering HPLC is one of the most powerful separation tools, and MS is good at sensitivity and specificity, HPLC coupled with MS (HPLC-ESI-MS) may be a best option for simultaneous determination of multiple metabolites in vivo. ...
Pharmacokinetic and metabolomic methods were employed to investigate the influence of caffeine on the sedative effects of promethazine. First, a space flight vigilance tasks simulation system and Standford sleepiness scale(SSS) were used to compare the effect of single administration of promethazine and combination administration with caffeine on the cognitive function of volunteers. Then software named Kinetica was used to calculate some of the important pharmacokinetic parameters of promethazine before and after the combination. And the possible influencing factors were discussed. Finally, a metabolomic method was applied to identify the potential biomarkers between two groups. The results suggest that caffeine could confront the sedative effects of promethazine and so improve the decreased cognitive function, which might be induced by the accelerated metabolism of promethazine and the altered dopamine, norepinephrine and epinephrine related pathways. This study provides a new approach for the research of combination administration of promethazine and caffeine.
... However, excessive amounts of caffeine would result in anxiety, uneasiness, heart palpitations, headaches, diarrhea, insomnia and many more. One will find the accounts on the fact that caffeine can have detrimental effects on human health in literature; these negative effects include exacerbating coronary artery disease, raising high blood pressure, and heightening the higher risk of heart attack and kidney disease [6,7]. This paper applies Taguchi method to consider the new extraction equipment that is designed to optimize the consistency of the coffee powder and extraction liquid to allow for a highly efficient extraction process. ...
In this paper, Taguchi method is applied to optimize ultrasound thermal process for extracting caffeine and flavor from coffee. The use of ultrasound can abridge experiments in cost, energy loss and time; the different operating conditions for extraction experiments are executed and the results are also compared. The results show that the best design factors for caffeine are 95℃ of extraction temperature, 28 kHz of operating frequency and 30 s of extraction time. The proposed optimized extraction method is efficient and energy-saving compared with the general process for making coffee.
... Some literature indicates that caffeine can have a detrimental effect on human health. These negative effects include exacerbating coronary artery disease, raising blood pressure, and heightening the risk of heart attack and kidney disease [1,2] The main ingredients of coffee include some flavor precursors (such as carbohydrates, sugars, amino acids, fats etc.). Today, at least 670 kinds of flavor compounds have been found [3]. ...
In this research, our focus is the use of ultrasound thermal process to extract flavor and caffeine from coffee. The different operating conditions for extraction experiments are executed and the results are also compared. The results show that coffee flavor is not enhanced with the increase of temperature because the volatile degree of coffee flavor components is quick and easy to be reached at high temperatures. From the experimental results, it can be found that using low vibration frequency is better than using high vibration frequency. Also, caffeine will be reached into the saturated state at the 15th second of the extracting time and the quantity of caffeine augments with the increase of temperature.
... The purpose of this research was to determine caffeine contents of Vietnamese coffee purchased at supermarket in Viet Nam (Dak Tin, Di Linh, Nam Nguyen, Origin and Vinacafe) at different temperature (80 °C, 90 °C and 100 °C), at different brewing times (1 min, 3 min and 5 min) and at different volume of water (30 ml, 70 ml and 150 ml) by UV/vis spectrophotometry, which is available in most laboratories. Although spectrophotometry is a fast and simple method, it is not possible to determine caffeine directly in coffees by conventional UV absorption measurement due to the spectral overlap (Zhang et al., 2005). ...
In this study, the caffeine contents in five certain Vietnamese coffee (Dak Tin, Di Linh, Nam Nguyen, Origin and Vinacafe) found in the Vietnamese market were determined using UV/vis spectrophotometry. The quantification of caffeine sample was calculated by standard addition method. Our results showed that the caffeine contents in coffee brewing were influenced by temperature of water used to brew, time of brewing, and independent on the volume of water, respectively. In general, higher concentrations of caffeine were found in all samples prepared at temperature 100°C for 5 minutes. The order of caffeine contents in coffee samples was Dak Tin, Di Linh, Nam Nguyen, Origin and Vinacafe, respectively. This study can contribute to a better knowledge of caffeine contents in Vietnamese coffee of Vietnamese consumers.
... A number of analytical techniques can be employed to find the caffeine contents, i.e., UV-vis spectrophotometry (Belay et al. 2008;Belay 2010;Atomssa and Gholap 2011), high-performance liquid chromatography (İçen andGürü 2009, 2010;Park et al. 2012), Fourier transform infrared (Ohnsmann et al. 2002;Mashkouri Najafi et al. 2003), Raman spectroscopy (Edwards et al. 2005;He´doux et al. 2011) and capillary electrophoresis (Zhang et al. 2005). Because of high consumption of tea, it is important to have an accurate and precise knowledge about its contents. ...
Pure caffeine was dissolved in four different solvents, i.e., distilled water, ethyl acetate, chloroform and dichloromethane; further, molar decadic absorption coefficient of each solvent was determined with the help of B eer– L ambert law. It was observed that dichloromethane was the best for decaffeination as compared with the other three solvents (i.e., distilled water, chloroform and ethyl acetate). Caffeine was extracted using dichloromethane from five famous tea brands, namely A lokozay, L ipton, T apal, T etley and PG TIPS . The amount of extracted caffeine was quantified by employing UV ‐vis spectrophotometric technique. The concentration of the caffeine in the tea solution was determined at different brewing time (2, 5, 10, 15, 20, 25 and 30 min) and temperature (90 and 30C). The caffeine contents in the commercial brands (i.e., A lokozay, L ipton, T apal, T etley and PG TIPS ) were found in the range between 1 and 5%.
Practical Applications
Caffeine becomes an important issue because of its utilization in pharmaceuticals. It is also an eminent fact that excessive amount of caffeine can be dangerous to human health. In addition, tea is one of the main sources of caffeine for human body. So, the present experimental studies are mainly focused to quantify and reduce the caffeine contents using a cost‐effective, accurate and precise way. For this purpose, an analytical technique, i.e., UV ‐vis spectrophotometry, used to determine the caffeine contents and solvent extraction process was employed to extract the caffeine from its tea aqueous solution.
... Up to now, theophylline analyses include electrospray ionisation ion mobility spectrometry (ESI-IMS) (Jafari, Rezaei, Javaheri, 2011b), high-performance liquid chromatographic method (Brunetto et al., 2007;Nirogi, Kandikere, Shukla, Mudigonda, Ajjala, 2007), spectrophotometry (Singh Sahu, 2006), poly(dimethylsiloxane) microchannel electrophoresis (Zhang, Lian, Wang, Chen, 2005), capillary electrochromatography (Chen, Zheng, Feng, 2010), and ion chromatography (Chen Wang, 2001). Unfortunately these techniques require expensive instruments, skilled operators, and are complicated procedures, which are generally not available in most laboratories. ...
A simply electrochemical method based on CdSe microparticles modified glassy carbon electrode (GCE) was developed to determine theophylline using cyclic voltammetry and differential pulse voltammetry. Theophylline showed a well-defined oxidation peak at the fabricated electrode in phosphate buffer solution and the oxidation peak current is much higher than that at the bare GCE, indicating that CdSe can effectively improve the oxidation of theophylline. Several effect factors on theophylline determination were optimised, such as CdSe amount, solution pH, scan rate and accumulation time. Under the optimal conditions, the oxidation peak current of theophylline was proportional to its concentration in the range of 1.0-40 and 40-700μM with a correlation coefficient of 0.9974 and 0.9956, respectively. The limit of detection was estimated to be 0.4μM (S/N=3). The developed method showed good reproducibility and excellent selectivity. The fabricated electrode was successfully used to determine theophylline in tea, carbonated cola drink, fruit juice drink, fermented milk drink and preserved fruit with acceptable recovery.
... Furthermore, UV-visible spectrophotometer is cheap and it is found in many laboratories. But caffeine content in tea leaves cannot be determined directly using UV-visible spectrometer due to the matrix effect of UV absorbing substances (Guzin, 2002; Zhang et al., 2005). Caffeine content in tea leaves can be obtained using UV-visible spectrometer by Beer-Lambert's law. ...
In this paper, oscillator strength of caffeine in dichloromethane, water, chloroform, and ethyl acetate were calculated in the wave number range of 32, 000 to 41,000cm -1 . It was found that oscillator strength of caffeine in dichloromethane, water, chloroform, and ethyl acetate were 0.230 ± 0.001, 0.170 ± 0.0003, 0.114 ± 0.001, 0.150 ± 0.001 respectively. Caffeine content of real tea leaves using integrated absorption coefficient method were also calculated for different samples at two different temperatures. The result agrees with that obtained using Beer's law with a little less in the case of integrated absorption coefficient technique with higher value at the boiling temperature and smaller extraction time.
An electrochemical sensor was fabricated by drop-casting ZnO/GO-phenol formaldehyde amine (ZnO/GO-PFA) nanocomposite onto graphite (Gr) electrode for the detection of caffeine. In this concern, the compositional features of the nanocomposite and their morphologies were examined by Fourier-transform infrared spectra (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and transition electron microscopy (TEM) techniques. The developed sensor exhibited strong electrocatalytic behaviour towards the oxidation of caffeine in phosphate buffer solution (PBS). EIS studies indicated a significant drop of charge transfer resistance (Rct) and cyclic voltammetry (CV) experiments showed a favourable ionic interaction between ZnO/GO-PFA and caffeine. Differential pulse voltammetry (DPV) exhibited a linearly varied oxidation peak with caffeine concentration range between 5 and 155 μM, leading to 0.15 μM detection limit. The improved surface area of the ZnO/GO in the developed sensor led to remarkable stability and repeatability which is attributed to the growth of controlled sized ZnO nanocrystals on the graphene oxide (GO) sheet. The practical applicability of the developed sensor was tested with urine sample with the recovery rate of more than 97 %, suggesting that the fabricated sensor can find potential application in the electroanalysis of caffeine in drugs and food samples.
Density functional theory calculations based on the TPSS functional were performed to investigate the potential application of the pristine AlN nanosheet (AlNNS) as well as the Au-decorated AlNNS (Au@AlNNS) in the detection of the theophylline (TP) drug. We found that the pristine sheet weakly adsorbed the drug, and its sensing response was about 6.0. After the Au-decoration on the AlNNS, the TP drug was powerfully adsorbed onto the Au@AlNNS with the adsorption energy of −1.33 eV, and the sensing response increased to 689.2. The localised molecular orbital energy decomposition analysis illustrated that the electrostatic attraction is stronger than the covalent interaction after the TP adsorption onto the Au@AlNNS. Based on the partial density of state analysis, the TP drug created a new state through the HOMO–LUMO gap of Au@AlNNS, which significantly increased the electrical conductivity. A short recovery time of 2.51 s was attained for the TP desorption from the Au@AlNNS surface. The water solvent weakened the adsorption process and decreased the sensing response to 524.6. Based on the results, we suggested the Au@AlNNS as a biosensor for the TP drug recognition.
Rosin-based polymer microspheres (RPMs) as stationary phases in HPLC were prepared using methyl acrylic acid as the functional monomer, ethylene glycol maleic rosinate acrylate as the cross-linker, and carboxylic group...
Caffeine is a common xanthine alkaloid found in tea leaves, coffee beans, and other natural plants, and is the most widely used psychotropic substance in the world. Accumulating evidence suggests that low plasma levels of caffeine and its metabolites may serve as reliable diagnostic markers for early Parkinson's disease patients. In this study, we demonstrated a new MEKC method for determining caffeine and its three main downstream metabolites, paraxanthine, theobromine and theophylline, in human plasma. Plasma samples were collected and analyzed after solid‐phase extraction, by using MEKC. The running buffer was composed of 35 mM phosphate, pH of 10.5, and 25 mM SDS. The separation voltage was 15 kV and the detection wavelength was at 210 nm. Under the optimum conditions, four distinct analytes were completely separated and detected in less than 12 min. Method limits of detection were as low as 7.5 ng/mL for caffeine, 5.0 ng/mL for theobromine and 4.0 ng/mL for both paraxanthine and theophylline. The recoveries were between 88.0%–105.9%. This method was successfully applied to 27 human plasma samples. The results indicate that the plasma concentrations of the four analytes are significantly lower in patients with early Parkinson's disease than in control subjects (p <0.05). The area under curve was improved to 0.839 when caffeine and its three main metabolites were included, suggesting that MEKC testing of caffeine, theophylline, theobromine, and paraxanthine may serve as a potential method for early diagnosis of Parkinson's disease.
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Device miniaturization is generally considered to improve the efficiency and throughput of instrumental chemical analysis. In this chapter, the power of miniaturization is examined from the viewpoint of microfabrication. Currently, microfabrication techniques are being increasingly applied to prepare fluidic arrays on silicon, glass, and polymer substrates with the final goal of realizing so called micro total chemical analysis systems (μTAS), also referred to as lab(oratory) on a chip. These miniaturized arrays aim at integration of multiple analytical unit operations on a single microfabricated chip (i.e., microchip), including sample preparation, injection, separation and detection. Sometimes reaction chambers are also implemented on the chip and integrated with on line sample preparation and/or separation systems. Although exploitation of microchip based analysis in small molecule analysis remains somewhat limited compared with proteomics, the vast potential of this technology is reviewed in the light of potential future applications in metabolomics. Often, examples are given to technological solutions which are not applied to metabolomics per se, but rather to related fields. Throughout this chapter, the emphasis is put on microchip electrophoresis (MCE) techniques. In addition, practical aspects related to pressurized methods, such as microchip liquid chromatography, are also presented. Microchip based off line and on line integrated sample clean up and preconcentration techniques are mainly touched upon where amenable to integration with a microfluidic separation system.
Caffeine is an alkaloid of the methylxanthine family known as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness in humans. There is a recommended upper limits of caffeine for health because a high dose can cause negative effects. Chlorogenic acid is a natural polyphenol compound known to have an antioxidant activity. In this study, the contents of caffeine and chlorogenic acid in coffee beans from different origins(Costa Rica, Indonesia, Vietnam) were determined by using liquid chromatography-tandem mass spectrometry(LC-MS/MS). The experiment offers more selectivity and sensitivity for those compounds compared with conventional methods such as UV/VIS spectrophotometry. The average concentrations of caffeine and chlorogenic acid in coffee beans origined in Costa Rica were 15.05 mg/g and 5.33 mg/g respectively. In the case of coffee beans origined in Indonesia, the average concentrations were 13.10 mg/g for caffeine and 3.75 mg/g for chlorogenic acid. Vietnamese coffee showed that the average concentrations were 17.79 mg/g for caffeine and 1.12 mg/g for chlorogenic acid. This study can contribute to a better understanding of the contents of caffeine and chlorogenic acid in various coffee beans in order to evaluate dietary intake.
High performance thin layer chromatographic (HPTLC) estimation of caffeine was carried out using HPTLC plate (silica gel 60 F254, 20 × 10 cm 2), solvent system [EtOH- EtOAc, 1:9 v/v] and scanned at λmax 275 nm. Caffeine exhibited R∫, value of 0.12 ± 0.01. Validation of the method in terms of linearity, accuracy and precision was carried out. For co-relating caffeine-frustration relationship single group repeated measures were designed for fifty subjects. Analysis of variance indicates that increase in unit dose (100 mg) of caffeine results into statistically significant increase in the frustration tolerance. However, more than 300 mg dose of caffeine showed no further increase in the frustration tolerance of the subjects. Our study reports that energy drinks selected for the study contains caffeine within prescribed WHO limit (300 mg/day).
Coffee, Tea and soft drinks are very commonly used beverages in all over the world. The caffeine is the main stimulant occurred in all drinks. Caffeine stimulates the central nervous system, relaxation, myocardial stimulation, recreation etc. It can provide energy, decrease fatigue, enhance performance etc. Caffeine having medicinal properties so can be used along with other drugs for headache, stimulation, muscle relaxant etc. Up to certain limit caffeine is useful but overdose of caffeine starts side effects on the human body. There are various instrumental methods can be used for the determination of caffeine in plants, coffee, tea, soft drinks and pharmaceutical formulation in presence of other drugs. HPLC methods are the most common, reliable methods for the determination caffeine in complex sample. Very low concentration of caffeine can be determined with high accuracy and precision. Here in this review we have summarized various HPLC methods used for the caffeine analysis in various samples and complex mixtures with their chromatographic column, mobile phase, flow rate, detector etc.
A simple and sensitive microfluidic capillary electrophoresis method with laser induced fluorescence detection was developed for the analysis of sulfonamides using fluorescein isothiocyanate as derivatization reagent. The performance of the system was demonstrated through the separation and determination of sulfamethazine, sulfamerazine and sulfamethoxazole in a running buffer solution containing 20 mmol/L borax (pH 9.2) with 15 % (v/v) ethanol. The injection and separation voltages, the concentration of borax, pH of the buffer and the content of ethanol in running buffer were optimized to get great influence on the separation. This proposed method showed satisfactory sensitivity with the limits of detection (S/N = 3) of 0.01 to 0.04 μmol/L for the sulfonamides. The method also exhibited very good reproducibility with the relative standard deviations of not more than 9.2 and 2.2 % for fluorescence intensity and migration time, respectively. The analysis was achieved within only 1.6 min.
A novel electrochemical sensor for the determination of theophylline based on ethylene glycol maleic rosinate acrylate as the cross linking agent and acrylic acid as functional monomer was fabricated by molecularly imprinted technology. A molecularly imprinted polymers (MIPs) membrane was synthesized on the surface of a glassy carbon electrode in vacuum drying oven by free radical polymerization method. The electrochemical behavior of the membrane was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry. Under optimum conditions, it was found that the response of peak currents was linear to the concentration of theophylline in range of 2.00 × 10-7~3.45 × 10-4 mol/L (linear regression coefficient=0.9961) with the detection limit of 1.00 × 10-7 mol/L. The sensor not only has high selectivity, but also shows good stability and reproducibility. The sensor was applied to the determination of theophylline in theophylline sustained release tablets samples with recovery ranging from 95.6% to 103.8%.
In recent years demands on the amount of information that can be obtained from the analysis of a single sample have increased. For time and economic reasons it is necessary to examine at the same time larger number of compounds, and compounds from different groups. This can best be seen in such areas as clinical analysis. In many diseases, the best results for patients are obtained when treatment fits the individual characteristics of the patient. Dosage monitoring is important at the beginning of therapy and in the full process of treatment. In the treatment of many diseases biogenic amines (dopamine, serotonin) and methylxanthines (theophylline, theobromine, caffeine) play an important role. They are used as drugs separately or in combination with others to support and strengthen the action of other drugs - for example, the combination of caffeine and paracetamol. Vitamin supplementation may be also an integral part of the treatment process. Specification of complete sample preparation parameters for extraction of the above compounds from biological matrices has been reviewed. Particular attention was given to the preparation stage and extraction methods. This review provides universal guidance on establishing a common procedures across laboratories to facilitate the preparation and analysis of all discussed compounds. Copyright © 2014 John Wiley & Sons, Ltd.
This article reports the electrochemical determination of caffeine in the presence of paracetamol (PA) using a self-assembled monolayer (SAM) of non-peripheral amine substituted copper(II) phthalocyanine (4α-CuIITAPc) on glassy carbon electrode (GCE). The 4α-CuIITAPc SAM modified GCE shows two pairs of redox waves at 0.16 V and 0.23 V, corresponding to CuII/CuI and Pc−1/Pc−2, respectively. The 4α-CuIITAPc SAM modified GCE exhibits an excellent electrocatalytic activity toward caffeine. Further, it was successively used for the selective and simultaneous determination of caffeine in the presence of PA. The differential pulse voltammetric current responses of caffeine were increased linearly while increasing the concentration of caffeine in the range of 0.005–1.4 mM and a detection limit was found to be 3.04 × 10−8 M (S/N = 3). Further, the modified electrode successfully recovers caffeine in blood serum samples. The present method was also applied for the determination of caffeine in cola drinks and simultaneous determination of caffeine and PA in pharmaceutical formulations. The results obtained from the present method were validated with the HPLC method.
Theophylline (1, 3-dimethylxanthine) is used both in the prophylaxis of chronic asthma and chronic obstructive airways disease (COAD), and to treat emergencies in acute severe asthma. Administration of theophylline to patients in respiratory distress can be fatal and, therefore, it is essential to know whether the person has achieved a theophylline blood concentration expected to produce therapeutic effects or otherwise. A method using sodium fluoride-preserved post-mortem blood samples has been established to enable evaluation (if theophylline levels in the blood at the time of death. The simple, rapid, and accurate high-performance thin-layer chromatography (HPTLC) method with UV-densitometric detection at 277 nm was validated for analysis of theophylline in postmortem blood. Theophylline was extracted at pH 8.5 with chloroform-isopropanol 8:2 from post-mortem blood after acid hydrolysis. Recovery ranged from 89.1 to 93.4% at a concentration of 10 mu g mL(-1) in the pH range 8.3 to 8.6. An average analytical recovery of 89.9% was achieved at pH 8.5 with a relative standard deviation of 2.2%. Chromatographic separation was performed on pre-coated silica gel 60F(254) plates, with chloroform-methanol 9:1 as mobile phase. Polynomial regression of the data points (0.5 to 20 mu g mL(-1)) for blood theophylline resulted in a calibration plot with a regression coefficient (r(2)) = 0.998 and the detection limit was 0.5 mu g mL(-1) (S/N= 3). Intra-day and inter-day repeatability ranged from 0.5 to 0.8% and from 0.5 to 1.3%, respectively, for three different concentrations in the range 0.5-10 mu g mL(-1). There was no evidence of degradation of theophylline either in the methanolic solution or during chromatography. The method is highly selective, because retardation factor (R(F)), peak resolution (R(S)), and peak purity were reproducible. The proposed method enables simple and rapid separation from post-mortem blood (completed in one hour after extraction), uses less solvent, and does not require an extensive clean-up procedure. The high sensitivity (LOD 0.5 mu g mL(-1)) is comparable with that of other chromatographic techniques.
To investigate the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine, this study uses a method based on microdialysis technique and liquid chromatography that allows continuous and concurrent in vivo monitoring of extracellular caffeine in the blood, brain and bile of anesthetized rats following the administration of caffeine (3 or 10mg/kg, i.v.) through the femoral vein. Dialysates of the blood, brain and bile were directly injected onto the liquid chromatographic system and no further clean-up procedures were required. The study design consisted of two groups of six rats in parallel: the rats of the control group received caffeine (3 or 10mg/kg, i.v.) alone and those of the cyclosporine treated-group were injected cyclosporine (10mg/kg, i.v.) 10min prior to caffeine administration (3 or 10mg/kg, i.v.). The decline of caffeine in the blood, brain striatum and bile suggested that caffeine had rapid exchange and equilibration between the peripheral compartment and the central nervous system. In addition, the results indicated that caffeine underwent hepatobiliary excretion and was distributed into brain. When cyclosporine was co-administered, the pharmacokinetic parameters were not significantly altered. The results of this study reveal that the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine might not relate to P-glycoprotein.
Methylxanthines (caffeine, theophylline, theobromine) are a popular group of natural purine alkaloids, which are components of many commonly used drugs, parapharmaceuticals and a wide range of food products (e.g. coffee, tea, energy drinks, etc.). Caffeine metabolites (theophylline, paraxanthine, theobromine and other 1-, 3-, 7-methyl tri-, di- and mono-derivatives of xanthine) and hypoxanthine metabolites (xanthine, uric acid) play an important role in the biochemical processes of mammalian organisms. That is why they are the markers of many diseases and are in the focus of the clinicians, pharmaceutical industry and ecologists. In addition to the natural methylxanthines there are structurally related synthetic derivatives: pentoxifylline, dyphylline, xantinol nicotinate and 8-chlorotheophylline that are still valuable pharmaceuticals needing to be monitored. A review of the modern techniques used for determination of methylxanthines for the last 10 years (2000 – March 2010) is presented.
In this work for the first time, simultaneous analysis of caffeine and theophylline was done by ion mobility spectrometry (IMS) only, without a powerful separation technique (e.g., HPLC). Ion mobility spectrometry with low cost, inexpensive maintenance and very fast analysis makes an attractive technique for the simultaneous determination of the caffeine and theophylline in foodstuff samples and biological matrices. In this study, the extraction protocol using molecular imprinted polymer-solid phase extraction (MIP-SPE) was successfully used to directly extract caffeine and theophylline from real samples. The results obtained provided the detection limits of 0.2 and 0.3μgmL−1 for caffeine and theophylline, respectively. The linear dynamic range of about two orders of magnitude was obtained for these compounds. Also, the proposed method was used to analyse various real samples of green tea and spiked human plasma, and the obtained results confirmed the capability of ESI-IMS for simultaneous detection of caffeine and theophylline.
In this work, we report a novel electrochemical RNA aptamer for the selective detection of theophylline. Firstly, gold nanoparticles were electrodeposited on the surface of glassy carbon (GC) electrode to form a gold nanoparticles modified electrode. Secondly, the designed single-stranded RNA (ssRNA) was immobilized on gold nanoparticles through a thiol linker as a probe RNA. Then, the complement stranded RNA, which can combine with the probe ssRNA to form a double-stranded RNA (dsRNA) with a recognition unit of theophylline, was linked on the probe RNA through a hybrid reaction in the presence of theophylline. Doxorubicin was selected as an electrochemical indicator. The proposed RNA aptamer presents an excellent selectivity for the detection of theophylline. The detectable concentration range of theophylline is from 2.0 to 50.0μM with a limit of detection of 1.2μM.
Molecular imprinting is a rapid developing method of obtaining synthetic receptors to a wide range of target molecules. In this work, a novel poly (vinyl alcohol) imprinted material has been obtained with caffeine used as template molecule. To demonstrate the obtaining of the molecular imprinted poly (vinyl alcohol), studies of caffeine sorption and desorption have been done. In order to determine the selectivity of the imprinted film, the sorption of other caffeine structurally related compounds such as theophylline, xanthine and theobromine has been performed.
Published data on the properties and determina-Published data on the properties and determina-tion of caffeine, theophylline, theobromine and some other tion of caffeine, theophylline, theobromine and some other methylxanthines in various objects are surveyed and methylxanthines in various objects are surveyed and described systematically. Different sample preparation pro-described systematically. Different sample preparation pro-cedures such as liquid extraction from solid matrices and cedures such as liquid extraction from solid matrices and liquid ± liquid, supercritical fluid and solid-phase extraction liquid ± liquid, supercritical fluid and solid-phase extraction are compared. The key methods of analysis including are compared. The key methods of analysis including chromatography, electrophoresis, spectrometry and electro-chromatography, electrophoresis, spectrometry and electro-chemical methods are discussed. Examples of methylxan-chemical methods are discussed. Examples of methylxan-thine determination in plants, food products, energy thine determination in plants, food products, energy beverages, pharmaceuticals, biological fluids and natural beverages, pharmaceuticals, biological fluids and natural and waste waters are given. The bibliography includes and waste waters are given. The bibliography includes 393 references 393 references. .
In recent years, ionic liquids (ILs), as green and designer solvents, have accelerated research in analytical chemistry. This review highlights some of the unique properties of ILs and provides an overview of the preparation and application of IL or IL-based materials to extract bioactive compounds in plants. IL or IL-based materials in conjunction with liquid-liquid extraction (LLE), ultrasonic-assisted extraction (UAE), microwave-assisted extraction (MAE), high performance liquid chromatography (HPLC) and solid-phase extraction (SPE) analytical technologies etc., have been applied successfully to the extraction or separation of bioactive compounds from plants. This paper reviews the available data and references to examine the advantages of IL and IL-based materials in these applications. In addition, the main target compounds reviewed in this paper are bioactive compounds with multiple therapeutic effects and pharmacological activities. Based on the importance of the targets, this paper reviews the applications of ILs, IL-based materials or co-working with analytical technologies. The exploitation of new applications of ILs on the extraction of bioactive compounds from plant samples is expected to increase.
The present study has concentrated on finding a new stationary phase in liquid chromatography. To improve the selectivity of monolithic column, a new ionic liquids–based (ILs-based) monolithic column (150 × 4.6 mm i.d.) is synthesized. Characteristic and evaluation of monolithic column are investigated by field emission-scanning electron microscopy (FE-SEM) and determination of caffeine and theophylline in high performance liquid chromatography (HPLC). FE-SEM images show that this monolithic column has a porosity structure. At the condition of mobile phase was 0.06 mol L−1 Na2HPO4 (pH 9.0) and flow rate was 0.7 mL min−1, a good linear relationship was demonstrated when the concentrations of caffeine and theophylline were in the range of 0.1–60.0 μg mL−1. These two compounds can obtain better resolution on the ILs-based monolithic column than non-ILs monolithic column, and the recoveries ranged from 97.40% to 108.00% and the interday and intraday relative standard deviations were less than 5%. The HPLC method, developed in this study, was proved to be acceptable for drugs assay, and this ILs-based monolithic column as the stationary phase was a potential tool for future HPLC separation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
A glass microchip is described in which reagents and serum samples for competitive immunoassay of serum theophylline can be mixed, reacted, separated, and analyzed. The device functions as an automated microfluidic immunoassay system, creating a lab-on-a-chip. Electroosmotic pumping was used to control first the mixing of 50-fold-diluted serum sample with labeled theophylline tracer in a 1:1 ratio, followed by 1:1 mixing and reaction with anti-theophylline antibody. The 51-nL on-chip mixer gave the same concentration as dilution performed off-chip, within 3%. A 100-pL plug of the reacted solution was then injected into an electrophoresis separation channel integrated within the same chip. Measurements of free and bound tracer by fluorescence detection gave linear calibration curves of signal vs log[theophylline] between 0 and 40 mg/L, with a slope of 0.52 +/- 0.03 and an intercept of -0.04 +/- 0.04 after a 90-s reaction time. A detection limit of 0.26 mg/L in serum (expressed before the dilution step, actual concentration of 1.3 micrograms/L at the detector) was obtained. Recovery values were 107% +/- 8% for 15 mg/L serum samples.
Capillary electrophoresis and related techniques on microchips have made great strides in recent years. This review concentrates on progress in capillary zone electrophoresis, but also covers other capillary techniques such as isoelectric focusing, isotachophoresis, free flow electrophoresis, and micellar electrokinetic chromatography. The material and technologies used to prepare microchips, microchip designs, channel geometries, sample manipulation and derivatization, detection, and applications of capillary electrophoresis to microchips are discussed. The progress in separation of nucleic acids and proteins is particularly emphasized.
The separation and determination of three alkaloids by micellar electrokinetic capillary chromatography (MECC) with amperometric detection (AD) was reported. A carbon disk electrode used as working electrode for the alkaloids exhibit good responses at +1175mV (versus Ag/AgCl). On a 70cm length, 25μm i.d. capillary, baseline separation is possible with a carrier solution containing 35mmol/l sodium dodecyl sulphate (SDS) in 20mmol/l, pH 8.5 phosphate buffer solution. The migration time and peak current of solutes increased markedly and decreased with increasing SDS concentration. Under the optimized conditions, the separation of three purine alkaloids was accomplished within 13min. The determination of them was performed by using good linearity between peak current and concentration for all three analytes with correlation coefficients from 0.9979 to 0.9993 and recoveries from 95.34 to 104.91%. The method was applied successfully to determine the active ingredients of the composite theophylline tablets and the assay results was satisfactory.
The separation of eight purine bases was achieved by capillary electrophoresis in 16 min using a voltage of 15 kV and a 50 mM sodium carbonate–hydrogencarbonate buffer at a pH of 10. Carbonate buffers have many advantages. They are non-toxic, inexpensive, easy to prepare and provide a stable, reproducible electroosmotic flow. Equilibration time after a sodium hydroxide rinse is minimal; thus the total analysis time is shorter than when an acidic buffer is used. No additives to the buffer are required to obtain the majority of the separations of interest and uncoated capillaries can be used. A group of eight purines and the naturally occurring pyrimidines were baseline separated. The linearity correlation for adenine in an optimized separation of the bases was 0.995 over two orders of magnitude. The daily reproducibility was 0.1% and day-to-day reproducibility was 2.5%.
Capillary zone electrophoresis is a highly efficient analytical technique that has been shown to be particularly useful for the analysis of isomers. Using a cathodic injection and anodic detection scheme, ortho-, meta- and para-hydroxybenzoic acids were separated in a fused-silica capillary column with a phosphate buffer at pH 10.3 (25.0 mmol/1 phosphate + 0.20 mmol/1 cetyltrimethylammonium bromide (CTAB) + 10% (v/v) 1-propanol with an applied voltage of 10 KV followed by direct UV detection. The use of CTAB as electroosmotic flow modifier allows the rapid separation of the three isomers by reversing the direction of electro-osmotic flow. The influence of pH, CTAB concentration and organic solvents on the migration behaviour of the solutes were also studied.
The electrokinetic separation behavior of positively chargeable substances with various hydrophobicities over the pH range 2-11 is described, using plain aqueous buffers, binary media with organic solvents, and systems with surfactants at concentrations between 0.0005 and 75 mM or other buffer additives. Examples studied include dextromethorphan, methadone, ketoconazole, itraconazole, amiodarone, and desethylamiodarone, compounds that play an important role in pharmacotherapy. Electrokinetic chromatography systems comprising dynamically formed micelles or ionic buffer additives that can form ion pairs with the solutes are shown to be unsuitable for the separation of highly hydrophobic, positively chargeable compounds, including the latter three drugs investigated. However, capillary zone electrophoresis (CZE) in binary systems with organic solvents (40-80%, v/v) at a buffer pH near or lower the solute's pK(a) values or CZE at low pH in the presence of an electrically neutral complexing agent, such as beta-cyclodextrin, can be employed effectively. Data presented illustrate that pK(a) values in binary systems with organic solvents that are more basic than water are smaller than those in aqueous media. Furthermore, somewhat less hydrophobic and positively chargeable compounds can be sufficiently dissolved in aqueous buffer at pH < pK(a) and can therefore be analyzed by CZE without any buffer additives.
Capillary zone electrophoresis (CZE) was adapted for the simultaneous determination of major components in green tea infusions. Separation was achieved using a fused-silica capillary column with a borax buffer at pH 8.0 and UV detection at 200 nm. The components analyzed were (−)-epicatechin, (−)-epigallocatechin, (−)-epicatechin gallate, (−)-epigallocatechin gallate, (+)-catechin, caffeine, theanine and ascorbic acid. The concentrations of these components were significantly different among various kinds of teas. CZE can be a very useful tool to estimate the quality and taste of green tea.
A selective and sensitive reversed-phase liquid chromatographic method was developed for the simultaneous analysis of [1-Me-14C]caffeine and its eight major radiolabelled metabolites in rat urine. The separation of the complex mixture of caffeine metabolites was achieved by gradient elution with a dual solvent system using an endcapped C18 reversed-phase column, which in contrast to commonly used C18 reversed-phase columns also allows the separation of the two isomers of 6-amino-5-(N-formylmethylamino)-1,3-dimethyluracil (1,3,7-DAU), a caffeine metabolite of quantitative importance predominantly occurring in rat. As caffeine is metabolised primarily by members of the cytochrome P450 1A (CYP1A) subfamiliy, determination of the pattern of caffeine metabolites in rat urine enables analysis of activities of this important enzyme subfamily in vivo. Since CYP1A is suggested to be involved in the detoxification of bilirubin, the assay may be applied to search for untoxic inducers of CYP1A which might be of pharmacological interest in the treatment of hyperbilirubinaemia.
HPLC in the reversed-phase mode is used to assay methylxanthines including theobromine, paraxanthine, theophylline and caffeine in urine. The calibration graphs show good linearity in the concentration range 0-10 micrograms/ml. The limit for accurate quantitation of theophylline was 0.25 microgram/ml. Between 6 and 20% of the parent drug is recovered in urine (0-12 h) after the oral administration of sustained release preparations containing 150 and 250 mg theophylline to four volunteers. Theophylline levels above 0.25 microgram/ml were found in 1539 out of 3885 urine samples collected from athletes during unannounced doping control in Flanders. Statistical evaluation of the results gives a far outside value [75th percentile+(3 x interquartile range)] of 2.25 micrograms/ml. The ratio theophylline paraxanthine (TP/PX) as an indicator for the non-dietary intake of theophylline seems to be more reliable. The far outside ratio was 0.20. To ensure with the greatest possible degree of certainty that no false-positive result is reported, decision limits of 5 micrograms/ml and 0.50, for theophylline and the ratio TP/PX respectively, are proposed.
A microchip capillary electrophoresis device has been used to separate the reaction products of homogeneous, immunological reactions within approximately 40 s. Determination of monoclonal mouse IgG in mouse ascites fluid, via a direct assay, and the drug theophylline in serum samples, via a competitive assay, was demonstrated on-chip. The mouse anti-bovine serum albumin IgG assay gave a linear calibration curve up to at least 135 micrograms/mL, with +/- 3% precision. The theophylline assay gave a threshold for detection of 1.25 ng/mL in diluted serum. A calibration curve of signal vs undiluted log[theophylline] is linear from 2.5 to 40 micrograms/mL, which includes the therapeutically useful range. Theophylline recoveries in spiked samples were 100%, within an experimental error of +/- 5%. A buffer system consisting of 0.05 M tricine adjusted to pH 8.0, 0.01% (w/v) Tween 20, and approximately 40 mM NaCl was used. This buffer allowed for adequate separation (40,000 plates for theophylline; 1000 plates for theophylline-antibody complex and for human IgG) and gave reproducibility of migration times of 1-1.5% over 4-day periods, indicating minimal problems from adsorption in the uncoated chips.
A capillary electrochromatography (CEC) method has been developed for the separation of theophylline, caffeine and five related drugs on a normal-phase column with UV or photodiode array detection. Several binary, ternary and quaternary mobile phase compositions are evaluated for optimal resolution and elution of these drug analytes. The importance of selecting suitable organic solvents, buffer electrolyte, pH and applied voltage is demonstrated by a systematic study. Excellent separation is achieved for the eight drugs using a ternary mobile phase composition of isopropanol/hexane/1 mM Tris (52:40:8, pH 8), with an efficiency of 63000 theoretical plates per meter at room temperature. Detection limits are typically at the low microg/mL level. The developed method is simple to use and it gives acceptable day-to-day reproducibility.
Capillary zone electrophoresis (CZE) devices fabricated in poly(dimethylsiloxane) (PDMS) require continuous voltage control of all intersecting channels in the fluidic network in order to avoid catastrophic leakage at the intersections. This contrasts with the behavior of similar flow channel designs fabricated in glass substrates. When the injection plugs are shaped by voltage control and leakage from side channels is controlled by the application of pushback voltages during separation, fluorescein samples give 64 200 theoretical plates (7000 V separation voltage, E = 1340 V/cm). Native PDMS devices exhibit stable retention times (+/- 8.6% RSD) over a period of five days when filled with water. Contact angles were unchanged (+/- 1.9% RSD) over a period of 16 weeks of dry storage, in contrast to the known behavior of plasma-oxidized PDMS surfaces. Electroosmotic flow (EOF) was observed in the direction of the cathode for the buffer systems studied (phosphate, pH 3-10.5), in the presence or absence of hydrophobic ions such as tetrabutylammonium or dodecyl sulfate. Electroosmotic mobilities of 1.49 x 10(-5) and 5.84 x 10(-4) cm2/Vs were observed on average at pH 3 and 10.5, respectively, the variation strongly suggesting that silica fillers in the polymer dominate the zeta potential of the material. Hydrophobic compounds such as dodecyl sulfate and BODIPY 493/503 adsorbed strongly to the PDMS, indicating the hydrophobicity of the channel walls is clearly problematic for CZE analysis of hydrophobic analytes. A method to stack multiple channel layers in PDMS is also described.
A micellar electrokinetic capillary chromatography (MEKC) method for the simultaneous analysis of five tea catechins, theanine, caffeine, gallic acid and ascorbic acid has been developed. The catechins are (-)-epicatechin, (+)-catechin, (-)-epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate. p-Nitrophenol serves as both reference and internal standard. All the components are separated within 13 min with a 57 cm uncoated fused-silica column. On-column detection was carried out at 200 nm. This method has been used to measure these compounds in fresh tea leaves and tea liquor. The limit of detection for all analytes ranged from 1 to 20 microg/ml.
The development of a poly(dimethylsiloxane)-based (PDMS-based) microchip electrophoresis system employing dual-electrode electrochemical detection is described. This is the first report of dual-electrode electrochemical detection in a microchip format and of electrochemical detection on chips fabricated from PDMS. The device described in this paper consists of a top layer of PDMS containing the separation and injection channels and a bottom glass layer onto which gold detection electrodes have been deposited. The two layers form a tight reversible seal, eliminating the need for high-temperature bonding, which can be detrimental to electrode stability. The channels can also be temporarily removed for cleaning, significantly extending the lifetime of the chip. The performance of the chip was evaluated using catechol as a test compound. The response was linear from 10 to 500 microM with an LOD (S/N = 3) of 4 microM and a sensitivity of 45.9 pA/microM. Collection efficiencies for catechol ranged from 28.7 to 25.9% at field strengths between 200 and 400 V/cm. Dual-electrode detection in the series configuration was shown to be useful for the selective monitoring of species undergoing chemically reversible redox reactions and for peak identification in the electropherogram of an unresolved mixture.
An HPLC method has been developed for the separation and the determination of caffeine and its metabolites in urine samples using a one extraction-analysis run and UV detection. The compounds were extracted by liquid-liquid extraction using chloroform-isopropylalcohol (85:15, v/v). Chromatographic separation was accomplished on an ODS analytical column with a mobile phase containing 0.05% acetic acid/methylalcohol (92.5:7.5, v/v). Compounds were monitored at 280 nm. The method was validated for the determination of AFMU, 1X, 1U, 17X and 17U caffeine metabolites required to assess the metabolic activity of the enzymes subject to in vivo caffeine testing. The validated assay was applied to urine samples from ten healthy volunteers. The method was proved to be suitable to assess simultaneously the enzymatic activity of cytochrome P450 CYP1A2 and CYP2A6, as well as N-acetyltransferase and xanthine oxidase.
This paper describes an improved method for filling microfluidic structures with aqueous solutions. The method, channel outgas technique (COT), is based on a filling procedure carried out at reduced pressures. This procedure is compared with previously reported methods in which microfluidic channels are filled either by using capillary forces or by applying a pressure gradient at one or more empty reservoirs. The technique has proven to be > 90% effective in eliminating the formation of bubbles within microfluidic networks. It can be applied to many devices, including those containing PDMS-terminated channel features, a single channel inlet, and three-dimensional arrays.
A fully disposable microanalytical device based on combination of poly(methylmethacrylate) (PMMA) capillary electrophoresis microchips and thick-film electrochemical detector strips is described. Variables influencing the separation efficiency and amperometric response, including separation voltage or detection potential are assessed and optimized. The versatility, simplicity and low-cost advantages of the new design are coupled to an attractive analytical performance, with good precision (relative standard deviation RSD = 1.68% for n = 10). Applicability for assays of mixtures of hydrazine, phenolic compounds, and catecholamines is demonstrated. Such coupling of low-cost PMMA-based microchips with thick-film electrochemical detectors holds great promise for mass production of single-use micrototal analytical systems.
We have demonstrated that precolumn derivatization and capillary electrophoresis separation on a poly(dimethylsiloxane) (PDMS) microchip can be realized as efficient as those on glass microchips. In an optimized condition of micellar electrokinetic chromatography (MEKC), using 25 mM sodium borate buffer (pH 10.0) with 25 mM sodium dodecyl sulfate (SDS) and 5% v/v methanol, the electroosmotic flow in an oxidized PDMS microchip is stabilized within 3% for days. By employing a fluorometric derivatization with o-phthaldialdehyde (OPA) in an optimally designed reaction chamber, four most important biogenic amines occurring in foods, histamine, tyramine, putrescine, and tryptamine, are quantitatively determined in less than 1 min at the levels applicable to real samples. The migration behaviors of anionic OPA-derivatized biogenic amines under the MEKC conditions are analyzed, and it has been found that under our separation conditions, the electrophoretic mobility of the SDS micelles is significantly greater than those of the anions in the aqueous phase. The channel manifold in a PDMS substrate is fabricated using replica molding against a thick photoresist, SU-8, pattern generated by photolithography. The plate with the microchannel pattern is strongly, irreversibly bonded to another PDMS plate by using a new bonding technique, which employs surface oxidation by corona discharge generated from a cheap, handy source, Tesla coil.
Separation and direct detection of amino acids, glucose and peptide in a 3.1 cm separation channel made of poly(dimethylsiloxane) (PDMS) with end-column amperometric detection at a copper microdisk electrode was developed. This system is the integration of a normal sized working electrode with electrochemical detection on a PDMS microfabricated device. The PDMS channels dynamically modified by 2-morpholinoethanesulfonic acid (MES) show less adsorption and more enhanced efficiency than that of unmodified ones when applied to separations of these biological molecules. The migration time is less than 100 s and the reproducibility of migration time is satisfactory with relative standard deviation (RSD) of 2.8% in 19 successive injections. The limits of detection of arginine (Arg), glucose, and methionine-glycine (Met-Gly) are estimated to be 2.0, 8.5, and 64.0 microM at S/N = 3, approximately 0.5-16.0 fmol, respectively. Variances influencing the separation efficiency and amperometric response, including injection, separation voltage, detection potential, or concentration of buffer and additive, are assessed and optimized.
The development of a microchip electrophoresis system involving integrated frequency based electrochemical detection is described. The use of poly(dimethylsiloxane) (PDMS) as the channel substrate greatly simplifies the fabrication process while decreasing cost and time consumption. Characterization of this system is accomplished through the detection of native carbohydrates at planar copper electrodes. Various photolithographic techniques are explored in the optimization of electrode area. Separation efficiency of 1 x 10(5) theoretical plates per meter is demonstrated. Sinusoidal voltammetry utilizes information in the frequency domain to achieve sensitive detection through either of two approaches, maximization of signal or minimization of noise. Mass detection limits (S/N = 3) of less than 200 amol have been accomplished for glucose and sucrose. Sinusoidal voltammetry also facilitated the selective isolation of an analyte signal from a pair of chromatographically unresolved species through the use of phase discrimination.
Microemulsion electrokinetic chromatography (MEEKC) was applied to the separation of six catechins and caffeine, the major constituents of the green tea. The developed methods involved the use of sodium dodecyl sulfate (SDS) as surfactant, n-heptane as organic solvent and an alcohol as cosurfactant. The separations were performed under acidic conditions (pH 2.5 phosphate buffer, 50 mM) to ensure good stability of the catechins, with reversed polarity (anodic outlet). The effect of the alcohol nature on the MEEKC selectivity was evaluated; nine alcohols were used as cosurfactant: 1-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, and cyclohexanol. The migration order of (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-gallocatechin (GC), (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), caffeine and theophylline was significantly affected by the alcohol used as cosurfactant. Using nine microemulsions, four different selectivities were achieved: A (cyclohexanol); B (2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol); C (1-butanol, 1-pentanol, cyclopentanol); D (tert-butanol). MEEKC methods, based on 2-hexanol and cyclohexanol as cosurfactant were validated and successfully applied to the analysis of catechins and caffeine in commercial green tea products.
Poly(dimethylsiloxane) microchip capillary electrophoresis with amperometric detection has been used for rapid separation and determination of acetaminophen and its hydrolysate, i.e. p-aminophenol. A Pt ultramicroelectrode with a diameter of 10 microm positioned at the outlet of the separation channel was used as a working electrode for amperometric detection. Factors influencing separation and detection were investigated and optimized. Results show that acetaminophen and p-aminophenol can be well separated within 35 s with RSD-1 (approximately 0.1 fmol) at S/ N=3. This method has been successfully applied to the detection of traces of p-aminophenol in paracetamol tablets.
This paper presents an electrochemical detector for poly(dimethylsiloxane) (PDMS) microchip CE with a three-dimensional adjustor which makes it possible to accurately align a separate working electrode that can be easily fabricated in laboratory to the uncertain PDMS microchannel outlet. The substantial influence of the electrode-PDMS microchannel distance was investigated. The optimal electrode-outlet distance was found to be 10 microm for the PDMS microchannel with the width of 50 microm due to its relatively slow electroosmotic flow. Adrenaline and catechol were well separated, with a linear response range from 20 microM to 1 mM, and a detection limit of 2 microM for catechol, using carbon disk electrode (diameter of 300 microm). Furthermore, arginine and histidine can be well separated and detected directly in the PDMS microchannel using a Cu disk electrode (diameter of 150 microm).
Separation and detection of proteins have been realized on nonionic surfactant-modified poly(dimethylsiloxane) (PDMS) microfabricated devices with end-column amperometric detection. The hydrophobic PDMS channels are turned into hydrophilic ones after being modified with Brij35 and facilitate the separation of proteins. The coating can remarkably reduce the adsorption of large protein molecules and is stable in the range of pH 6-12. The detection of proteins in such channels needs less rinsing time and thus efficiency is raised. Even large molecules of proteins can also be detected with better reproducibility and enhanced plate numbers. The relative standard deviation (RSD) of the migration time for glucose oxidase (GOD) is 2.2% (n = 19). Separation of GOD and myoglobin has been developed in modified channels. Predominant operational variables, such as the coating conditions, the concentration of surfactant and buffer, are studied in detail.
Significant progress in the development of miniaturized microfluidic systems has occurred since their inception over a decade ago. This is primarily due to the numerous advantages of microchip analysis, including the ability to analyze minute samples, speed of analysis, reduced cost and waste, and portability. This review focuses on recent developments in integrating electrochemical (EC) detection with microchip capillary electrophoresis (CE). These detection modes include amperometry, conductimetry, and potentiometry. EC detection is ideal for use with microchip CE systems because it can be easily miniaturized with no diminution in analytical performance. Advances in microchip format, electrode material and design, decoupling of the detector from the separation field, and integration of sample preparation, separation, and detection on-chip are discussed. Microchip CEEC applications for enzyme/immunoassays, clinical and environmental assays, as well as the detection of neurotransmitters are also described.
We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 microM to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument.
In this work, we establish an indirect amperometric detection method via mounting a single carbon fiber disk working electrode in the end part of a microchannel. This in-channel configuration for microchip capillary electrophoresis brings about that the potential of the working electrode in the case of electrochemical reduction reaction is coupled by the separation electric field, while the potential of the working electrode in the case of electrochemical oxidation reaction is not coupled by the separation electric field. Such a special performance provides a convenient and sensitive approach for indirectly detecting nonelectroactive analytes that relies on amperometric response of dissolved oxygen in solution and directly detecting electroactive analytes based on their own amperometric response on the carbon fiber electrode. This method has shown its essential importance in the analysis of inorganic cations, biomolecules, and electroosmotic flow rates. Based on preliminary results, a detection limit of 1.0 microM for K(+) and Na(+) have been achieved.