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Electrophoretic separation environmentally important phenolic compounds using montomorillonite-coated fused-silica capillaries
Abstract
This paper reports a simple procedure for coating fused-silica capillaries with poly(diallyldimethyl ammonium chloride) and montmorillonite. The coated capillaries were characterized by performing EOF measurements as a function of buffer pH, number of layers of coating, and number of runs (stability). The coated capillaries showed a highly stable μEOF (run-to-run RSD less than 1.5%, n = 20), allowing continuous use for several days without conditioning. The coated capillaries were then used for the effective separation of nine environmentally important phenolic compounds showing a significant improvement in the resolution, when compared to bare fused-silica capillaries. The EOF of the coated capillaries was constant in alkaline solutions (pH ≥ 7), allowing the optimization of the separation conditions of phenolic compounds without significantly affecting the μEOF.
... EOF can be increased by adding the anionic surfactant sodium dodecyl sulfate in a running buffer. Anionic surfactant, poly(diallyldimethylammonium chloride) and montmorillonite coated fused-silica capillaries showed a highly stable EOF (run-to-run RSD less than 1.5%, n = 20) and high separation efficiency [346] . Similarly , polyanions of poly(acrylamide-co-2-acrylamido-2- methyl-1-propanesulfonate) (PAMAMPS) bi-layer reveal stable μEOF ranges from -5 10 -5 to 35 10 -5 cm 2 V -1 s -1 in the CE microfluidic device [347] . ...
Rashid, M. et. al. (2010) 'Recent developments in polymer microfluidic devices with capillary electrophoresis and electrochemical detection', Micro and Nanosystems, 2(2), pp.108-136. Abstract: We review recent work on the development of polymer microfluidic devices using capillary electrophoresis (CE) for fluid driving and separation and electrochemical detection (ED). A variety of commonly used off-chip and inte-grated electrochemical detection approaches, including amperometric, conductimetric and potentiometric detection ap-proaches, have been given. We describe fabrication approaches for the creation of microfluidic architecture in a polymer substrate and electrode integration. The methods for polymer surface modification to enhance the microfluidic device properties are also described as well as developments in power supply for the creation of a robust CE-ED microfluidic de-vice system. A variety of applications are described for the CE-ED systems.
... For that reason, a variety of techniques have been used for delivery and control of liquids in CE-sensors and other microfluidic devices. Among others [30,188189190191, a description of the principles and some applications of electrophoretic, electro-osmotic, opto-acoustic, opticallydriven , electrochemical, and gravity-driven pumps has been recently published [25]. Because they do not require moving parts (motors, actuators, or check valves) and can be controlled with the same instrumentation used to power separation, most pumps used in CE and μchip- CE devices are electro-osmotically-driven. ...
Over the last years, there has been an explosion in the number of developments and applications of CE and microchip-CE. In part, this growth has been the direct consequence of recent developments in instrumentation associated with CE. This review, which is focused on the contributions published in the last 5 years, is intended to complement the articles presented in this special issue dedicated to instrumentation and to provide an overview of the general trends and some of the most remarkable developments published in the areas of high-voltage power supplies, detectors, auxiliary components, and compact systems. It also includes a few examples of alternative uses of and modifications to traditional CE instruments.
A simple, rapid, capillary zone electrophoresis method was developed and validated for the analysis the two of novel aminoalkanol derivatives (I) and (II) of 1,7‐diethyl‐8,9‐diphenyl‐4‐azatricyclo[5.2.1.02,6]dec‐8‐ene‐3,5,10‐trione, which were found in earlier studies as potential anticancer drugs. Samples were analyzed to demonstrate the specificity and stability indicating ability of the developed method. The samples were extracted using n‐hexane‐ethyl acetate mixture in the ratio of 90:10. Electrophoretic separation was performed on a eCAP fused silica capillary (37 cm length, 50 µm inside diameter) with a 50 mM tetraborate buffer as a background electrolyte adjusted to pH = 2.5. The separation time of (I) and (II) was achieved within 7 min. In addition, analysis of the two compounds in the serum was conducted. Limits of detection of (I) and (II) by UV absorbance at 200 nm were achieved in the range of 87.4–92.1 ng/mL. The sufficient recovery was observed in the range of 90.3–99.8%. The quantification limits for the compounds (I) and (II) were in the range of 279.71–291.03 ng/mL respectively. The method has been successfully applied to the analysis of compounds (I) and (II) in serum samples. This article is protected by copyright. All rights reserved
The chapter is an update of a previously published one, covering the literature up to the autumn of 2014 and following the same guidelines for the selection of analytical methods, namely: A section dealing with detection and determination of specific metal phenolates, a section dealing with conversion of the metal cation analytes into complexes with phenolic ligands before end analysis and a section presenting the use of certain metal phenolates as analytical aids and tools. For the sake of a more complete coverage, formation of anion–phenol and molecule–phenol complexes were also considered. In addition, a section is dedicated to the analytical aspects of ammonium phenolates, especially quaternary ammonium phenolates.
KEYWORDS
Metal phenolate analysis, chromogenic sensors, fluorogenic sensors, optodes, ion-specific electrodes, electrochemical analysis, extraction, chromatography, metal–phenol complexes, quaternary ammonium–phenol complexes, anion recognition, molecule recognition.
Inherently trace-level concentration of pollutants in the environment, together with the complexity of sample matrices, place a strong demand on the detection capabilities of electromigration methods. Significant progress is continually being made, widening the applicability of these techniques, mostly capillary zone electrophoresis, micellar electrokinetic chromatography, and capillary electrochromatography, to the analysis of real-world environmental samples, including the concentration sensitivity and robustness of the developed analytical procedures. This chapter covers the recent major developments in the domain of capillary electrophoresis analysis of environmental samples for pesticides, polycyclic aromatic hydrocarbons, phenols, amines, carboxylic acids, explosives, pharmaceuticals, and ionic liquids. Emphasis ismade on pre-capillary and on-capillary chromatography and electrophoresis-based concentration of analytes and detection improvement.
The addition of surfactants to the separation electrolyte is one of the most convenient ways to modify the electro‐osmotic flow (μEOF) in capillary electrophoresis. However, surfactants spontaneously adsorb to most surfaces; therefore, their presence in the running electrolyte may also affect the electrochemical detection. Changes in selectivity and sensitivity due to dynamic coating of electrode surfaces have been systematically reported during the last 30 years. In this review, some pertinent papers related to the use of surfactants to perform dynamic coatings of the capillary surface are discussed. The proposed mechanisms to explain the enhancements produced by surfactants at the detection step are also discussed along with some specific applications. A particular emphasis was placed on recent reports from our group dealing with the effects of anionic surfactants on the separation and detection of phenolic compounds.
Recent developments in materials, surface modifications, separation schemes, detection systems and associated instrumentation have allowed significant advances in the performance of lab-on-a-chip devices. These devices, also referred to as micro total analysis systems (µTAS), offer great versatility, high throughput, short analysis time, low cost and, more importantly, performance that is comparable to standard bench-top instrumentation. To date, µTAS have demonstrated advantages in a significant number of fields including biochemical, pharmaceutical, military and environmental. Perhaps most importantly, µTAS represent excellent platforms to introduce students to microfabrication and nanotechnology, bridging chemistry with other fields, such as engineering and biology, enabling the integration of various skills and curricular concepts. Considering the advantages of the technology and the potential impact to society, our research program aims to address the need for simpler, more affordable, faster and portable devices to measure biologically active compounds. Specifically, the program is focused on the development and characterization of a series of novel strategies towards the realization of integrated microanalytical devices. One key aspect of our research projects is that the developed analytical strategies must be compatible with each other; therefore, enabling their use in integrated devices. The program combines spectroscopy, surface chemistry, capillary electrophoresis, electrochemical detection and nanomaterials. This article discusses some of the most recent results obtained in two main areas of emphasis: capillary electrophoresis, microchip-capillary electrophoresis, electrochemical detection and interaction of proteins with nanomaterials.
Despite multiple orbiter and landed missions to extraterrestrial bodies in the solar system, including Mars and Titan, we still know relatively little about the detailed chemical composition and quantity of organics and biomolecules in those bodies. For chemical analysis on astrobiologically relevant targets such as Mars, Europa, Titan, and Enceladus, instrumentation should be extremely sensitive and capable of analyzing a broad range of organic molecules. Microchip capillary electrophoresis (μCE) with laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant markers but, to date, has lacked the necessary degree of automation for spaceflight applications. Here we describe a fully integrated microfluidic device capable of performing automated end-to-end analyses of amino acids by μCE with LIF detection. The device integrates an array of pneumatically actuated valves and pumps for autonomous fluidic routing with an electrophoretic channel. Operation of the device, including manipulation of liquids for sample pretreatment and electrophoretic analysis, was performed exclusively via computer control. The device was validated by mixing of laboratory standards and labeling of amino acids with Pacific Blue succinimidyl ester followed by electrophoretic analysis. To our knowledge, this is the first demonstration of completely automated end-to-end μCE analyses on a single, fully integrated microfluidic device.
Microfluidic and nanofluidic systems are dominated by fluid-wall interactions due to enormous surface-area-to-volume ratios in these devices. Therefore, strategies to control wall properties in a reliable and repeatable manner can be important for device operation. Chemical modification of surfaces provides one such method. However, the stability of the surface adhered layers under fabrication and likely device operating conditions have not been evaluated in depth. This paper presents the stability analysis of three surface layers used in the 'click' chemistry methodology for surface modification. The three surface layers have bromo, amine, and methyl termination on glass surfaces. All three surface groups are exposed to various wet and dry conditions including acid, base, solvent, electrolyte buffer solutions, oxidative plasmas, UV light, and thermal processing conditions. Contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were used to quantify the stability of the adhered surface layers. The data show that the brominated surface was stable to most test conditions, while both the amine and methyl surface layers were stable to a narrower set of test conditions.
A novel open tubular (OT) column covalently modified with hydrophilic polysaccharide, carboxymethylchitosan (CMC) as stationary phase has been developed, and employed for the separations of basic proteins and opium alkaloids by capillary electrochromatography (CEC). With the procedures including the silanization of 3-aminopropyltrimethoxysilane (APTS) and the combination of glutaraldehyde with amino-silylated silica surface and CMC, CMC was covalently bonded on the capillary inner wall and exhibited a remarkable tolerance and chemical stability against 0.1 mol/L HCl, 0.1 mol/L NaOH or some organic solvents. By varying the pH values of running buffer, a cathodic or anodic EOF could be gained in CMC modified column. With anodic EOF mode (pH<4.3), favorable separations of basic proteins (trypsin, ribonuclease A, lysozyme and cytochrome C) were successfully achieved with high column efficiencies ranging from 97,000 to 182,000 plates/m, and the undesired adsorptions of basic proteins on the inter-wall of capillary could be avoided. Good repeatability was gained with RSD of the migration time less than 1.3% for run-to-run (n=5) and less than 3.2% for day-to-day (n=3), RSD of peak area was less than 5.6% for run-to-run (n=5) and less than 8.8% for day-to-day (n=3). With cathodic EOF mode (pH>4.3), four opium alkaloids were also baseline separated in phosphate buffer (50 mmol/L, pH 6.0) with column efficiencies ranging from 92,000 to 132,000 plates/m. CMC-bonded OT capillary column might be used as an alternative medium for the further analysis of basic proteins and alkaline analytes.
A multi-functional open-tubular (OT) column covalently modified with [3-(phenylamino)propyl]trimethoxysilane (PPTMS) via a single-step silanization reaction has been developed, and employed for alkaloids and aromatic acids analytes by CEC. Both anodic and cathodic EOF could be gained in the PPTMS-bonded column, and anodic EOF was exhibited when the pH of running buffer was less than 8.0. Using thiourea as the EOF marker, a satisfactory column stability was denoted, and the RSD values for migration time and peak area were gained at 0.5 and 3.7% (intra-day, n=5), 1.7 and 5.6% (inter-day, n=3), 3.9 and 5.8% (column-to- column, n=16 in four batches). With anodic EOF mode (pH=2.0 of 10 mmol/L phosphate buffer), favorable separations of cationic alkaloids (viz. uridine, adenosine, cytidine, adenine, cytosine) were successfully achieved with column efficiencies ranging from 95 000 to 187 000 plates/m, and the undesired adsorption on the inter-wall of capillary column could be avoided. Besides, six anionic aromatic acids could be also separated efficiently in the co-electroosmotic mode with anodic EOF. And high efficiencies ranged from 176 000 to 235 000 plates/m were gained with a good repeatability. PPTMS-bonded capillary column might be used as an alternative functional medium to physical coating capillary column for the analyses of aromatic organic acids and bases.
Ordered, hexagonal, mesoporous metal (Ti, Zr, V, Al)-phosphonate materials with microporous crystalline walls are synthesized through a microwave-assisted procedure by using triblock copolymer F127 as the template. Corresponding metal chlorides and ethylene diamine tetra(methylene phosphonic acid) are chosen as the inorganic precursors and the coupling molecule, respectively. X-ray diffractometry, transmission electron microscopy, N(2) sorption, and thermogravimetry measurements confirm that the obtained metal phosphonates possess a hierarchically porous structure with pore sizes of 7.1-7.5 nm and 1.3-1.7 nm for mesopores and micropores, respectively, and the metal phosphonate materials are thermally stable up to around 450 °C with the pore structure and hybrid framework well preserved. Magic angle spinning NMR, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses indicate that the phosphonate groups are homogenously incorporated into the hybrid framework of the obtained materials. For the first time, the mesoporous hybrid materials are employed as the stationary phase in open tubular capillary electrochromatography technique for the separation of various substances including acidic, basic, and neutral compounds. These materials show good selectivity and reproducibility for this application.
In this paper, the fabrication of a wireless mobile unit containing an electrochemical detection module and a 3-channel high-voltage power supply (HVPS) designed for microchip CE is described. The presented device consists of wireless global positioning system controlled robotics, an electrochemical detector utilizing signal conditioning analog circuitry and a digital feedback range controller, a HVPS, an air pump, and a CE microchip. A graphical user interface (LabVIEW) was also designed to communicate wirelessly with the device, from a distant personal computer communication port. The entire device is integrated and controlled by digital hardware implemented on a field programmable gate array development board. This lab-on-a-robot is able to navigate to a global position location, acquire an air sample, perform the analysis (injection, separation, and detection), and send the data (electropherogram) to a remote station without exposing the analyst to the testing environment.
The stationary phases including the nonpolar and polar stationary phases in microscale separations have been greatly developed. This review describes the recent progress of the polar stationary phases (PSPs) with the focus on their preparation and the interesting applications in the field of CEC and capillary liquid chromatography (CLC) covering the literatures from the middle of 2006 to the middle of 2008. The PSPs described herein were summarized into three types as open-tubular, particle-packed and monolithic stationary phases for either CEC or CLC, and the separation mechanisms are of hydrophilic interaction, chiral selection, ion-exchange and/or electrostatic interaction, etc. After overviewing the literatures published in the last 2 years, the research efforts on PSPs for CEC and CLC have been remaining in the fabrication of open-tubular and monolithic capillary columns; whereas, the research endeavor of PSPs on particulate-packed format seemed to decline most likely due to the commercial availability of various packing particles for CEC and CLC.
A novel, simple, and economical method for the preparation of open-tubular capillary column using polydopamine coating was reported for the first time. After the capillary was filled with dopamine solution for 20h, polydopamine was formed and deposited on the inner wall of capillary as permanent coating via the oxidation of dopamine by the oxygen dissolved in the solution. Moreover, the electroosmotic flow of the coated capillaries was measured to be dependent on the repetitive coating times. The performance of the polydopamine-coated capillary electrochromatography was validated by the analysis of four auxins, indole-3-butyric acid (IBA), 2,4-dichlorophenoxyacetic acid (dCPAA), indole-3-acetic acid (IAA), and phenoxyacetic acid (PAA). The precisions (RSD, n=5) were in the range of 1.6-2.4% for migration time, 4.0-6.5% for peak area response, and 3.6-4.7% for peak height response for the four auxins at 1microgmL(-1) level. The detection limits were 0.185, 0.172, 0.177, and 0.259microg/mL for IBA, dCPAA, IAA, and PAA, respectively. The method was successfully used to the determination of IAA in the culture media of IAA-producing bacteria.
The effects of different surfactants (sodium 2-ethylhexyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate and sodium tetradecyl sulfate) on the analysis of phenolic compounds by microchip-CE with pulsed amperometric detection were investigated. Using sodium decyl sulfate as a model surfactant, the effects of concentration and pH were examined. Under the optimized conditions, the analysis of six phenolic compounds was performed and compared with control runs performed without surfactant. When these surfactants were present in the run buffer, decreases in the migration time and increases in the run-to-run reproducibility were observed. Systematic improvements in the electrochemical response for the phenolic compounds were also obtained. According to the results presented, surfactants enhance the analyte-electrode interaction and facilitate the electron transfer process. These results should allow a more rational selection of the surfactants based on their electrophoretic and electrochemical effects.
Recent advances in CE and CEC separation, detection and sample preparation/preconcentration methodologies, for the determination of a variety of compounds having current or potential environmental relevance, have been overviewed. The reviewed literature has illustrated the wide range of CE applications available, indicating a continuing interest in CE and CEC in the environmental field. New developments in chip-based CE systems are also discussed.
A novel cationic polymer coating that exhibits a fast anodal electroosmotic flow (EOF) has been developed for capillary electrophoresis.
In the first approach, poly(diallyldimethyl-ammonium chloride) is chemically bonded onto the interior capillary wall; in a
second approach, the polymer is physically adsorbed onto the inner wall of the capillary. Capillaries modified by both approaches
exhibit an anodal EOF in the pH range of 2.2–8.8, with a relatively pH-independent EOF (approximately −5.5 × 10−4 cm2/V s) over the pH range of 2.2–5.5. The application of the novel EOF-reversed phase is demonstrated by the improved separation
of basic proteins and beta-adrenergic blocking drugs. Separation efficiencies ranging from 50,000 to 200,000 plates per meter
are observed for proteins. The relative standard deviation (RSD) of migration times for multiple injections of test proteins
is less than 0.65%. The reproducibility of capillary synthesis is 2.3% RSD for capillaries synthesized on three different
days. The lifetimes of both the bonded and physically coated capillaries exceed 40 h of continuous use at 240 V/cm at pH.
Determination of environmental pollutants utilizing biodetectors such as bioassays, biomarkers, enzyme immunoassays (EIAs), or other bioanalytical tools is a continuously growing area. The present literature review describes the principles and advantages/limitations of several bioanalytical detection methods (BDMs) for the screening and diagnosis of dioxin and dioxin-like compounds. This study characterizes briefly the family of dioxin and dioxin-like compounds, discusses potential Ah receptor (AhR) ligands and cytochrome P-450 (CYP) 1A1-enzyme-inducing compounds. ‘Milestones’ in the development of BDMs are summarized and explained in detail for a number of bioanalytical tools that can be used to detect these classes of dioxin-like persistent bioaccumulative toxicants (PBTs). The design of a screening profile with a battery of bioassays/biomarkers coupled with the chemical analysis is evaluated. The relative potencies (REPs) to 2,3,7,8-TCDD for dioxin-like compounds are reviewed for various BDMs and the differences are noted.
During the last several years, illegal commercial application of methyl parathion (MP) in domestic settings in several U.S. Southeastern and Midwestern States has affected largely inner-city residents. As part of a multiagency response involving the U.S. Environmental Protection Agency (U.S. EPA), the Agency for Toxic Substances and Disease Registry (ATSDR), and state and local health departments, our laboratory developed a rapid, high-throughput, selective method for quantifying p-nitrophenol (PNP), a biomarker of MP exposure, using isotope dilution high-performance liquid chromatography-tandem mass spectrometry. We measured PNP in approximately 16,000 samples collected from residents of seven different states. Using this method, we were able to receive sample batches from each state; prepare, analyze, and quantify the samples for PNP; verify the results; and report the data to the health departments and ATSDR in about 48 hr. These data indicate that many residents had urinary PNP concentrations well in excess of those of the general U.S. population. In fact, their urinary PNP concentrations were more consistent with those seen in occupational settings or in poisoning cases. Although these data, when coupled with other MP metabolite data, suggest that many residents with the highest concentrations of urinary PNP had significant exposure to MP, they do not unequivocally rule out exposure to PNP resulting from environmental degradation of MP. Even with their limitations, these data were used with the assumption that all PNP was derived from MP exposure, which enabled the U.S. EPA and ATSDR to develop a comprehensive, biologically driven response that was protective of human health, especially susceptible populations, and included clinical evaluations, outreach activities, community education, integrated pest management, and decontamination of homes.
Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
Positively charged polydiallyldimethylammonium chloride, P, was found to bind strongly to the surface of anionic montmorrillonite, M, platelets in aqueous dispersions up to a saturation (estimated to correspond to the binding of five P to one 1.0 nm × 200 nm M platelet) beyond which reversible physisorption occurred. Immersion of a substrate (glass, quartz, silica-wafer, gold, silver, and even Teflon) into an aqueous 1% solution of P and rinsing with ultrapure water for 10 min resulted in the strong adsorption of a 1.6 nm thick P on the substrate. Immersion of the P coated substrate into an aqueous dispersion of M and rinsing with ultrapure water for 10 min led to the adsorption of 2.5 nm thick M. Repeating the self-assembly steps of P and M for n number of times produced (P/M)n self-assembled films. Thickness of the M layer was found to depend on the external voltage applied during its self-assembly: applying a positive potential during the self-assembly of M increased the thickness of the M layer; application of a small negative potential decreased it slightly; however, larger negative voltages augmented it. The structure of self-assembled (P/M)n films have been characterized by a variety of techniques: X-ray diffraction, X-ray reflectivity, atomic force microscopy, transmission electron microscopic, and surface plasmon spectroscopic measurements. It was shown that clay platelets form stacks upon adsorption to the polymer layer consisting on the average two aluminosilicate sheets. The evolution of the surface roughness upon sequential deposition of P/M layers was observed by in situ AFM. Large etched pits, up to 700 nm diameter and 30 nm depth, were smoothed during P/M deposition. Small pits (188 nm diameter and 14 nm deep) were capped after one P/M deposition cycle. Surface roughness of (P/M)n films was estimated by a number of methods including surface plasmon spectroscopy. The overall roughness did not appear to correlate with the type of substrate used. On the other hand, application of an external electric field during the self-assembly of P strongly influenced the surface morphology. Application of a negative potential during the self-assembly of P improved the uniformity and regularity of the deposited layers.
An on-line preconcentration technique based on 5 ml sample or standard solution injection onto a preconcentration column has been developed for the ion chromatographic (IC) determination of 14 chlorophenolic and phenolic compounds at the picomolar levels. A suitable gradient program using 10 mM sulphuric acid and variable concentrations of acetonitrile (36–65% (v/v), details given) was applied at the constant flow rate of 1.0 ml min−1. For the detection of 14 phenolic compounds, dc amperometric detection with a glassy carbon working electrode at the potential of +1.2 V versus Ag/AgCl reference electrode was used. The overall repeatability (n=5) for retention times was better than 0.6% and the repeatability (n=5) for the peak areas ranged from 0.5% (resorcinol) to 3.2% (3,5-dichlorophenol) at 50–250 nM concentration levels. LODs (3 S/N) of 200–500 pM except for 2,6- and 3,5-dichlorophenol and 2,3,5,6-tetrachlorophenol (1, 5 and 1 nM, respectively) were obtained. The method has been applied to determine some of the decomposition products of UV-irradiated fungicide tecnazene (1,2,4,5-tetrachloro-3-nitrobenzene) solution and phenolic pollutants in drinking water. Due to the high selectivity of the amperometric detection, the only compounds that can be determined are the ones that can be oxidised and therefore possible interferences (e.g. from nitro-compounds) are bypassed.
The title book covers coordination chemistry of the hydrous oxide-water interface; surface charge and the electric double layer; adsorption; chemical weathering phenomena; homogeneous and heterogeneous nucleation and precipitation; particle-particle interaction; carbonate reactivity; redox processes mediated by surfaces; photochemistry; and trace element transport. It can be used as a source book for teaching and for professionals in geochemical and environmental disciplines.
Reversed phase high-performance liquid chromatographic (RP-HPLC) methods are proposed for the analysis of phenol, thymol, chlorocresol and chloroxylenol in commercial pharmaceutical dosage forms. The use of 1-fluoro-2,4-dinitrobenzene as UV labelling reagent in pre-column derivatization has been investigated. The compound reacts rapidly (2min) under mild conditions (ambient temperature or 40°C) with phenols to give ethers that can be separated by RP-HPLC and detected at 292nm. The other procedure involves a post-column on-line photochemical conversion. A photoreactor was arranged between the analytical column and the fluorescence (λex=270nm, λem=310nm) and UV-diode array (λ=270nm) detector to enhance the performance of the methods. Additional informations of the analyte structure and photoreactivity by UV spectra (photoreactor ‘on’ and ‘off’) were obtained. The methods showed good selectivity and sensitivity.
Phenol-formaldehyde mixtures are widely used in a variety of applications, such as flame-retardant or adhesives. This kind of resin can also be used as surface protecting polymers for glassy carbon electrodes when they are applied to phenol oxidative processes. The purpose of this work was to obtain the best conditions for phenol (and two derivatives) determination with a phenol-formaldehyde modified glassy carbon electrode in flow injection analysis (FIA) with amperometric detection and to compare these results with those obtained with two different modifiers, 4-hydroxybenzaldehyde and 4-hydroxybenzoic acid, under the same conditions. Linear relationships were obtained in the 0.1 to 1.0 mu M phenol (or derivative) concentration range, the optima experimental conditions being 1.11 ml min(-1), 0.700 V (vs. Ag/AgCl/NaCl 3 M), with an electrodeposited charge of the modifier of 1.10 C cm(-2) and using an aqueous buffer (0.10 M total phosphate+0.05 M KCl, pH=7.0) as carrier solution.
Fused silica capillaries coated with thin films of physically adsorbed charged polymers are employed for capillary zone electrophoretic separations. The coating is a polyelectrolyte multilayer, constructed in situ by alternating rinses with positively and negatively charged polymers. The thickness of the multilayer and amount of surface charge is controlled by the concentration of salt in the deposition solutions. The direction of the electroosmotic flow oscillates as the multilayer surface charge alternates in polarity during buildup. The apparent surface charge, deduced from the electroosmotic mobility, is considerably less than the nominal surface charge of the film. Mechanisms limiting this apparent surface charge for a buffer-permeable layer are discussed. The multilayer-coated columns exhibit many desirable features in addition to ease of construction and reproducible control of electroosmotic flow: stable flow rates are achieved immediately on exposure of the column to running buffer, and reversed flow is possible. Columns are also found to be stable to extremes of pH and ionic strength, and to dehydration/rehydration. A series of basic proteins are separated with good efficiency, demonstrating column resistance to irreversible protein adsorption. Partitioning and separation of neutral solutes using thicker films is demonstrated.
A fully automated method for the rapid determination of organic acids (citric-, malic- and tartaric acid) and sugars (glucose, fructose, and sucrose) in soft drinks by sequential injection Fourier transform infrared (FTIR) spectroscopy is presented. A convective interaction media (CIM) disc carrying quaternary amino moieties was added as a solid phase extraction column to the flow system. Upon injection of a sample the organic acids were completely retained on the CIM disc whereas sugars passed to the flow cell. The organic acids were subsequently eluted by injection of an alkaline (pH 8.5) 1 M sodium chloride solution and recorded in their fully deprotonated form as a second flow injection peak. In both cases, the FTIR spectra corresponding to the peak maxima were selected for data evaluation. Two partial least squares models, one for sugars and the other for organic acids, were constructed based on the analysis of standards containing all six analytes. The developed method was applied to natural samples yielding results which were in good agreement with those obtained by an external reference method (enzymatic test kits). Deviations in the results were 3.4. and 4.1% for citric and malic acid and ranged from 4.7–5.1% for the sugars. The developed method is characterized by its short analysis time, experimental simplicity and its potential applications in routine analysis and process control.
Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
The effect of pH and ionic strength on the migration of neutral acids in capillary zone electrophoresis (CZE) has been studied for several phenols. The mobilities of the phenols and the efficiency of the capillary have been related to the studied factors. The mobility can be related to the pH of the running buffer through the mobility of the phenolate ion, and the conditional acidity pK value of the phenol at the working ionic strength. This allows prediction of the migration of the phenol, solely from its pKa′ value (literature pKa corrected for the ionic strength of the solution) and mobility of the anion, which can be easily calculated from the mobility at a basic pH value and the pKa′ value. Combination of the predicted mobility with the efficiency allows estimation of the resolution of the consecutive peaks obtained for a mixture of phenols. This method has been tested for two groups of phenols of environmental interest.
A simple and fast method for the simultaneous determination of the antioxidants propyl gallate (PG), octyl gallate (OG), lauryl gallate (LG), and nordihydroguaiaretic acid (NDGA) has been established by using microchip micellar electrokinetic chromatography with pulsed amperometric detection. Under the optimum conditions (30 mM borate buffer, pH 9.7, 30 mM sodium dodecyl sulfate, separation voltage of 1200 V and 5 s injection time) the analytes were baseline separated. Linear relationships were found between the concentration and peak current for all the selected antioxidants. The measured detection limits (S/N ≥ 3) of PG, OG, LG, and NDGA were 2.2, 1.4, 2.3, and 4.6 μM, respectively, which corresponds to 2–6 fmol of analyte. This approach has remarkable advantages with respect to other methodologies involving separations and electrochemical detection including minimal sample consumption, higher analysis speed, lower cost, and portability. Additionally, a highly reproducible signal (migration time and peak current) was obtained for a series of injections (n = 30). In order to demonstrate the capabilities of the method, the determination of antioxidants in a commercial food sample is also presented.
A simple and fast method, based on the use of micellar electrokinetic capillary chromatography in combination with UV detection, was developed for the determination of Sudan dyes (I, II, III and IV). The separation of a mixture of the four standards was achieved using a background electrolyte consisting of 5 mM borate (pH 9.3), 20 mM sodium dodecyl sulfate and 20% acetonitrile. Under optimized conditions, the four azo-dyes were baseline separated in 20 min with limits of detection ranging from 96 to 610 μg/L (S/N > 3). The applicability of the method for rapid screening and determination of Sudan dyes (I, II and III) was studied by analyzing spiked chili powder samples from India, Pakistan, Mexico, United States, Canada, and China.
A capillary electrophoretic method using a phosphate-based carrier electrolyte and direct UV detection at pH 6.5 for the routine determination of five organic acids in wine samples is described. The present method shows advantages over other commonly applied method based on phthalic acid buffer with indirect UV detection for the quantification of organic acids. Factors that affect capillary electrophoretic separation such as concentration and pH of the background electrolyte, concentration of the electroosmotic flow modifier, and methanol addition were considered. Separation and determination of tartaric, malic, acetic, succinic and lactic acids were achieved in approximately 6 min. The method was quantitative, with recoveries in the 98–107% range, and linear over more than one order of magnitude. The precision is better than 0.94–1.06% for migration time and 0.40–0.96% for peak area. The method is sensible, with detection limits between 0.015 and 0.054 mg L−1. The usefulness of the method was successfully demonstrated by the analysis of the considered organic acids in 39 red wines from two different Spanish Certified Brands of Origin (CBO). Determinations were made by direct injection after the appropriate sample dilution and filtration. Distributions of organic acids in Ribeira Sacra wines show a predominance of lactic (3784–452 mg L−1) and tartaric acids (1987–866 mg L−1) followed by succinic (897–398 mg L−1), malic (2844–not detected mg L−1) and acetic (749–116 mg L−1) acids. An analogous distribution was observed in the Bierzo wines: lactic acid (4037–179 mg L−1), tartaric acid (1819–772 mg L−1), succinic acid (646–389 mg L−1), malic acid (1513–not detected mg L−1) and acetic acid (553–214 mg L−1).
We have been investigating alternate assembling of inorganic materials, SiO2 nanoparticles, clay microplate, and polyoxometalates with oppositely-charged polyions. In this paper, previously reported results are summarized and compared in order to establish a unified interpretation. Reproducible film growth is observed in assembly of anionic SiO2 particles and cationic poly(diallyldimethylammonium chloride) (PDDA). The adsorption time required for successful assembly of SiO2 nanoparticles is only 2 s. Scanning electron microscopic (SEM) observation shows that the obtained film has a surprisingly flat surface. Similarly montmorillonite clay microplate is successfully assembled with cationic PDDA and poly(ethyleneimine) (PEI), but its adsorption required 5–6 min. These adsorption kinetics are interpreted based on the nature of the adsorbent. Adsorption of rigid and spherical SiO2 particles is diffusion-limited and very fast, probably because the relaxation process is not conceivable during the adsorption. In contrast, relaxation processes may play an important role in the adsorption of planar clay plates, as suggested previously for adsorption of organic polyions. Multilayer films of molybdenum oxide are prepared by alternate adsorption of ammonium octamolybdate ((NH4)4[Mo8O26]) and poly(allylamine) hydrochloride (PAH). Adsorption of molybdenum oxide does not show saturation. Protonation and condensation of the molybdenum oxide are probably accelerated on the pre-adsorbed molybdenum surface, resulting in film growth without saturation.
The preparation, characterization, and sorption properties for Ni(II) of combined phases of iron oxyhydroxide and montmorillonite were investigated. Two different preparation procedures were explored. In the first method, Fe(III) was contacted with montmorillonite at pH 2.5, and ferrihydrite was formed on the montmorillonite surface by slowly raising pH to 8.0 (Fe–mont). In the second method, O2 was bubbled through a solution (pH 7.0) containing Fe(II) and montmorillonite. This caused Fe(III) to precipitate as lepidocrocite (lep–mont). Batch adsorption experiments and the physical chemical properties of the solids, e.g. specific surface area, the point of zero charge, and the particle size distribution reflected a varying degree of interaction among the phases. In the Fe–mont system, a ferrihydrite coated montmorillonite surface was created. The result was an increase in specific surface area and sorption capacity for Ni(II) compared to the pure solids. The isoelectric point observed was typical for pure ferrihydrite. In the lep–mont system, predominantly separate phases of lepidocrocite and montmorillonite were created. The specific surface area, the isoelectric point, and the sorption capacity were significantly better predicted given the properties and weight fractions of the individual phases.
A simple method for the preparation of a polyethyleneimine (PEI) coating on the inner surface of fused-silica capillaries for capillary electrophoresis (CE) is reported. The PEI layer can be coated on the silica surface by just flushing the capillary with a solution containing high-molecular-mass PEI. The physically adsorbed layer appears to be very stable and can be used in a pH range of 3–11. In comparison to described methods to fabricate an immobilized PEI layer, the proposed method does not require an immobilization step, is simple and the preparation time of the coating is less than two hours. Good reproducibilities of migration times of basic proteins and peptides were obtained on the same PEI-coated capillary as well as on different PEI-coated capillaries. For basic proteins efficiencies ranging from 300 000–500 000 plates per meter were normally found.
A capillary zone electrophoretic method for the simultaneous analysis of inorganic anions, organic acids, amino acids and carbohydrates was developed with indirect UV detection using 2,6-pyridine dicarboxylic acid as the background electrolyte. This is the first paper to report their simultaneous analysis. Highly alkaline conditions were used in order to confer a negative charge not only on inorganic and organic anions but also on amino acids and carbohydrates, and to promote their migration towards the anode. Electroosmotic flow was reversed in the direction of the anode by adding cetyltrimethylammonium hydroxide to the electrolyte. Outstanding separations were obtained and electrophoretic mobilities of 82 compounds including nine inorganic anions, 23 organic acids, 18 amino acids and 32 carbohydrates were determined by the method. Under the optimized conditions 43 compounds were well separated in a single run. The relative standard deviations (n=5) of the method were better than 0.5% for migration times and between 0.8% and 4.9% for peak areas except for a few compounds. The detection limits for anions and amino acids were in the range from 6 to 12 mg/l and for carbohydrates from 23 to 35 mg/l with 300 mbar·s pressure injection (6 nl) at a signal-to-noise ratio of three. This method could be readily applied to the simultaneous determination of inorganic anions, organic acids, amino acids and carbohydrates in soy sauce, nutrient tonic and pineapple.
Montmorillonite is the most often studied swelling clay mineral. The layers have permanent negative charges due to isomorphic substitutions, and pH-dependent charges develop on the surface hydroxyls at the edges. Wyoming montmorillonite samples with different extents of isomorphic substitutions (Swy-1 and Swy-2) were studied. The acid–base titration of Na-montmorillonite suspensions between pH 4 and 9 at 0.01, 0.1 and 1 M NaCl was used to characterize pH-dependent charge development on amphoteric edge sites and to determine the point of zero charge (PZC) of edges. The evaluation of reversible net proton surface excess vs. pH functions revealed that the OH groups at edges having PZC at pH ∼6.5 are less basic than the –OH and less acidic than the –OH groups. Positive charges can develop in a protonation reaction of –OH sites at edges only at pHs below ∼6.5, and deprotonation of –OH then that of the –OH sites takes place with increasing pH of solution resulting in negative charges at edges. Therefore, patch-wise charge heterogeneity of montmorillonite, i.e. oppositely charged surface parts of layers, exists only under acidic conditions. Coagulation kinetics measurements resulted in reliable stability ratio data for fine montmorillonite sols at different pHs, and provided undisputable characterization of hetero- and homocoagulation. Edge-to-face heterocoagulation occurs above NaCl concentration 25–26 mmol l−1 at pH ∼4, where the hidden electric double layer (edl) of positively charged edge region has emerged. Edge-to-face attraction between the poorly charged edges and negatively charged faces of platelets around the pH of PZC of edges (pHPZC, edge∼6.5) in relatively low concentration of the indifferent electrolytes (typically around 50 mmol l−1 NaCl) is probable. The homocoagulation of uniformly charged lamellae at pH 8–8.5, formation of face-to-face aggregates requires much higher salt concentration (typically around 100 mmol l−1 NaCl) to compress the dominant edl on the highly charged faces of particles. XRD patterns of montmorillonite films prepared from slightly acidic suspensions proved that formation of well-ordered layer packages is hindered by the attraction between edges and faces. Characteristic changes in gel formation and in rheological properties induced by decreasing pH in dense suspensions containing 0.01 M NaCl provided experimental evidence for the structure of particle network. A significant increase in thixotropy and yield values, and also the formation of viscoelastic gels only below pH ∼6.5 verify that attractive interaction exists between oppositely charged parts of lamellar particles.
This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in situ intercalative polymerization and melt intercalation. The whole range of polymer matrices is covered, i.e. thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the separated, individual silicate layers are more or less uniformly dispersed in the polymer matrix. This new family of materials exhibits enhanced properties at very low filler level, usually inferior to 5wt.%, such as increased Young’s modulus and storage modulus, increase in thermal stability and gas barrier properties and good flame retardancy.
Phenol, a monohydroxy derivative of benzene, occurs naturally in animal waste and by decomposition of organic wastes. It is also produced by man, originally by fractional distillation of coal tar, but more recently by cumene hydroperoxidation and toluene oxidation. As a result of large production volume and natural sources, occupational and environmental exposure to phenol is likely. Phenol poisoning can occur by skin absorption, vapor inhalation, or ingestion, and, regardless of route of exposure, can result in detrimental health effects. Acute toxicity has been observed in man and experimental animals, resulting in muscle weakness, convulsions, and coma. In addition, studies have shown that although teratogenic effects have not been associated with exposure to phenol by either inhalation or oral route, high doses of phenol are fetotoxic. This paper addresses these studies and others in an attempt to determine if human health is at risk to those levels of phenol present in the environment and workplace. However, because data are limited, further research is necessary to analyze the mutagenic and carcinogenic potential of this chemical.
Phenol, a waste product of industrial processes that is introduced into aquatic ecosystems, adversely affects the indigenous biota, including algae, protozoa, invertebrates, and vertebrates. In addition to overt toxicities, phenol causes many subtle effects to the biota, such as reduced fertility, decreased survival of the young, and inhibition of growth. The toxicity of phenol to the aquatic biota is modified by several abiotic (e.g., dissolved oxygen, salinity, water hardness, temperature) and biotic (e.g., age, size, nutritional status) factors. Phenol is also produced commercially and has many uses which bring it into direct contact with human beings. It is rapidly absorbed through the skin and by inhalation through the lungs. Upon absorption of moderate amounts of phenol, it is detoxified by conjugation with sulfuric and glucuronic acids and excreted in the urine. High exposures to phenol may be fatal to human beings; infants appear to be hypersusceptible to phenol. Although phenol is a tumor promoter, it is not a carcinogen, cocarcinogen, or teratogen and, most probably, is not a mutagen.
The adsorption of proteins with net positive charges (pI > pH) on the walls of fused-silica capillaries is a common problem in the analysis of proteins by capillary electrophoresis. This paper explores the use of polycationic polymers as noncovalent coatings to limit this problem. The behavior of three sets of proteins was compared using uncoated and coated capillaries: (i) a protein charge ladder obtained by acetylation of lysozyme (EC 3.2.1.17); (ii) a protein charge ladder obtained by acetylation of carbonic anhydrase II (EC 4.2.1.1); (iii) a test panel of proteins with a range of values of molecular weight and pI. Four polycationic polymers were examined: polyethylenimine (PEI; MWav = 15000), Polybrene (MWav = 25000), poly(methoxyethoxyethyl)ethylenimine (MWav = 64000), and poly(diallyldimethylammonium chloride) (MWav = 10000). Detection of proteins with high pI was readily achieved using the first three of these polycationic polymer coatings but not with the poly(diallyldimethyl-ammonium chloride). Examination of the stability of these coatings indicates that they are robust: the change in electroosmotic flow was less than 10% for 25 replications of the same separations, using capillaries coated with PEI or Polybrene. This study demonstrates that the charge ladder obtained by acetylation of lysozyme is a good model with which to test the efficiency of polycationic coatings. A study of the electrophoretic mobilities of the members of this charge ladder at pH 8.3 determined the effective charge of lysozyme (Zp(0) = +7.6 +/- 0.1) and established the acidity of the alpha-ammonium group of lysozyme (pKa = 7.8 +/- 0.1). Results from the test panel of proteins suggest that protein adsorption is mainly driven by electrostatic interactions.
The long term stability of a commercial polyamine coated capillary (eCAP) is described. The capillary, which can be used in the CZE and MEKC mode, is based on coating with a polyamine after conditioning with 1 M NaOH and regeneration of this coating after each run. The stability was tested over 6 months on the drug trimethoprim and the R.S.D. values for migration time and peak area were 2.86 and 3.62% respectively (n = 8, each time of determination) (> 600 sample injections over the period). This stability was utilised in the validated method developed for trimethoprim and four of its related impurities. The repeatability of peak area for trimethoprim (without normalisation or external standard) was, within-day R.S.D. = 1.02% (n = 8) and between-days R.S.D. = 2.02% (n = 8 each day). Linearity was good (for 50 micrograms ml-1 target) (y = 249.6x + 17.3 (r = 0.992, n = 6). These results for trimethoprim and for other drug mixtures were comparison with conventional capillaries and the advantage of reducing the polyamine treated eCAP capillary to a minimum length is described, to achieve rapid assay of the 5 component timethoprim mixture in < 2 min.
Two procedures for the derivatization of the inner wall of fused-silica capillaries for the analysis of peptides and proteins by capillary electrophoresis (CE) at neutral pH are presented. In the first procedure, polyethyleneimine (PEI) is covalently attached to the capillary wall. In the second procedure, PEI is additionally cross-linked. We present analysis of standard peptides and proteins by CE using the coated capillaries. These coatings will have application for the separation of protein complexes at neutral pH, prior to analysis by electrospray mass spectrometry.
This review summarizes the various aspects of conducting electrokinetic chromatography in coated columns with suppressed electroosmotic flow. The specific features of the technique will be presented and the potential applications explored. The equations of migration, resolution and zone spreading for neutral solutes will be presented, compared, and contrasted with those of conventional electrokinetic chromatography in bare-silica columns. The principle of separation is the same in electrokinetic chromatography with or without electroosmotic flow; however, there are many significant differences that will be highlighted.
A coated capillary modified with a cationic polymer was developed by using a novel coating procedure, successive multiple ionic-polymer (SMIL) coating. The SMIL coating was achieved by first attaching the cationic polymer to the capillary inner wall, and then the anionic polymer to the cationic polymer layer, and finally the cationic polymer to the anionic polymer layer. The stability of Polybrene (PB)-modified capillary made by SMIL coating was remarkably improved in comparison with a conventional PB-modified capillary. It endured during 600 replicate analyses and also showed strong stability against 1 M NaOH and 0.1 M HCl. The relative standard deviation of the run-to-run, day-to-day, and capillary-to-capillary coating was all below 1%, and good reproducibilities were obtained. The PB-modified capillary made by SMIL coating was applied to the basic protein analyses. It gave good performances for the protein analyses even when the pH of the electrolyte was near the isoelectric point (pI) of the protein. In addition, 0.1 M NaOH rinse prior to the sample injection allowed the reproducible analysis of a highly adsorptive sample such as plasma because the adsorbed sample could be flushed out of the capillary. Besides protein analyses, an efficient analysis of the cationic drugs by capillary electrophoresis/mass spectrometry (CE/MS) was also possible.
A capillary gas chromatographic (GC) method for the simultaneous determination of organic acids, sugars, and sugar alcohols extracted from plant tissues is described. Plant leaves were extracted in 5% (w/v) perchloric acid and neutralized extracts were purified using C18 cartridges. Organic acids, sugars, and sugar alcohols in purified extracts were converted to their trimethylsilyl (TMS)/TMS-oxime derivatives prior to separation and detection by capillary GC with flame ionization detection (FID). Derivatization procedures were investigated in detail and the compounds of interest were readily converted to their TMS/TMS-oxime derivatives using hexamethyldisiazane reagent in acetonitrile solvent (1:6 v/v) at 100 degreesC for 60 min. The derivatives were sufficiently volatile and stable. The FID response to derivatized compounds was generally linear in the concentration range 30-300 microg ml-1, with detection limits in the order of 3-76 ng. The proposed method was demonstrated for the determination of organic acids, sugars, and sugar alcohols in leaf extracts of two native Australian plants.
New acrylic polymers bearing oxirane groups were synthesized to be used in the production of coated capillaries. A fully automated coating procedure was devised based on the use of diluted water solutions of these polymers. The whole procedure required less than 30 min. The new polymers rapidly adsorbed from water onto the capillary wall, thus suppressing electroosmotic flow (EOF) to a negligible value. The adsorbed coatings were stable for hundreds of hours at high pH, temperature, and in the presence of 8 M urea. Efficient separations of acidic and basic proteins were achieved in the new phases.
The double-chained cationic surfactant didodecyldimethylammonium bromide (DDAB) was found to form more stable coatings onto the walls of CE capillaries than similar single-chained surfactants such as cetyltrimethylammonium bromide (C16TAB). After removing DDAB from the buffer, the reversed EOF decreased only 3% over 75 min under continuous electrophoretic conditions. Also, the reversed EOF is 60% greater for DDAB than for C16TAB at pH 2. This greater coating stability is associated with a different aggregate structure for the surfactant at the capillary surface. The more homogeneous coating and greater surface coverage provided by DDAB allows the excess surfactant to be flushed from the capillary prior to performing electrophoretic separations. Separations of a basic protein mixture yielded quantitative recoveries, efficiencies ranging from 560,000 to 750,000 plates/m, and migration time reproducibility of 0.8-1.0% RSD (n = 10). This performance is similar to that of adsorbed cationic polymers (Polybrene, polyethyleneimine) but is achieved using a coating procedure that is over 10 times faster.
Poly(dimethylsiloxane) (PDMS) capillary electrophoresis (CE) microchips were modified by a dynamic coating method that provided stable electroosmotic flow (EOF) with respect to pH. The separation channel was coated with a polymer bilayer consisting of a cationic layer of Polybrene (PB) and an anionic layer of dextran sulfate (DS). According to the difference in charge, PB- and PB/ DS-coated channels supported EOF in different directions; however, both methods of channel coating exhibited a pH-independent EOF in the pH range of 5-10 due to chemical control of the effective zeta-potential. The endurance of the PB-coated layer was determined to be 50 runs at pH 3.0, while PB/DS-coated chips had a stable EOF for more than 100 runs. The effect of substrate composition and chip-sealing methodology was also evaluated. All tested chips showed the same EOF on the PB/DS-coated channels, as compared to uncoated chips, which varied significantly. No significant variation for separation and electrochemical detection of dopamine and hydroquinone between coated and uncoated channels was observed.
As microchip technology evolves to allow for the integration of more complex processes, particularly the polymerase chain reaction (PCR), it will become necessary to define simple approaches for minimizing the effects of surfaces on the chemistry/processes to be performed. We have explored alternatives to silanization of the glass surface with the use of additives that either dynamically coat or adsorb to the glass surface. Polyethylene glycol, polyvinylpyrrolidone (PVP), and hydroxyethylcellulose (HEC) have been explored as potential dynamic coatings and epoxy (poly)dimethylacrylamide (EPDMA) evaluated as an adsorbed coating. By carrying out analysis of the PCR products generated under different conditions via microchip electrophoresis, we demonstrate that these coating agents adequately passivate the glass surface in a manner that prevents interference with the subsequent PCR process. While several of the agents tested allowed for PCR amplification of DNA in glass, the EPDMA was clearly superior with respect to ease of preparation. However, more efficient PCR (larger mass of amplified product) could be obtained by silanizing the glass surface.
This review article describes the preparation of dynamic and static polymeric wall coatings for capillary electrophoresis. Properties of bare fused-silica surfaces and methods for the characterization of capillary coatings are summarized. The preparation and basic properties of neutral and charged wall coatings are considered. Finally, advantages and potential applications of various coatings are discussed.
The present review highlights the mechanisms of action and efficiency of three major classes of dynamic coatings so far adopted in capillary electrophoresis: (i) amines to oligo-amines, (ii) neutral synthetic and natural polymers, and (iii) neutral and zwitter-ionic surfactants. Their merits and efficacy have been explored in depth via a novel quantitation technique consisting of eluting, by frontal analysis, any adsorbed proteinaceous material, which can then be correctly quantified as a peak as it moves in front of the detector window. This is achieved by loading sodium dodecyl sulfate (SDS) micelles onto the cathodic side and migrating them electrophoretically into the capillary lumen, where they efficiently sweep any adsorbed polypeptide material. It is found that a common trend, for all quenchers, is linked to a hydrophobicity scale: the more hydrophobic the inhibitor, the better it minimizes potential interactions of macromolecules with the wall. This seems to be true for all the classes of dynamic modifiers tested. Finally, we describe a novel, dynamic to static quencher: it is a quaternary piperazine, bearing a reactive iodine atom at the end of a butyl tail (N(methyl-N-omega-iodo-butyl),N'-methyl piperazine). This molecule first binds to the wall, at alkaline pH values, via ionic and hydrogen bonds. Once docked onto the wall, the reactive tail forms a covalent link with the silica surface, to which it then remains permanently affixed.
A flow injection analysis-capillary electrophoresis system has been used for on-line flow stacking of 11 US Environmental Protection Agency priority phenol pollutants. Samples containing low concentrations of phenols dissolved in deionised water are continuously delivered to the capillary opening by means of a peristaltic pump. The sample components stack at the boundary between the highly conductive separation electrolyte and the introduced sample. By selecting an appropriate electrolyte and stacking conditions the movement of the electrolyte solution inside the capillary can be reduced, thereby improving the stacking efficiency. The electrolyte used here contained 20 mM phosphate, 8% 2-butanol, and 0.001% hexamethonium bromide at pH 11.95, and the stacking was carried out at 2 kV for 240 s. These conditions allowed up to 2000-fold preconcentration of the selected phenols. No matrix removal was necessary.
Potentiometric detection employing coated-wire electrodes was applied to the determination of organic acids in liquid chromatography (LC). Poly(vinyl chloride)-based liquid membranes, incorporating lipophilic macrocyclic hexaamines as neutral ionophores were used as electrode coatings. The selectivity and sensitivity of the macrocycle-based electrodes were found to be superior to an electrode based on a lipophilic anion exchanger (a quaternary ammonium salt). Sensitive detection was obtained for the di- and tricarboxylic acids tartaric, malonic, malic, citric, fumaric, succinic, pyruvic, 2-oxoglutaric and maleic acids after separation in reversed-phase LC. Detection limits (signal/4sigmanoise=3) of 6 pmol for malonic acid and 2 pmol for maleic acid were attained. The detection was explained using a molecular recognition model. The hexaamine-based potentiometric electrodes had a 1-s response time at 1 ml min(-1) flow-rates. They were stable for at least 4 months, with an intra-electrode variation of 3.2% (n=5).
In order to develop an advanced analytical method using capillary electrophoresis (CE) for non-volatile environmental pollutants such as endocrine disruptors, combination with mass spectrometry (MS) is necessary for their identification. We chose dichlorophenols (DCPs) as test samples because one of their isomers, 2,4-DCP, is suspected to have endocrine disrupting effects. A preliminary study on their separation by CE-MS was performed using a laboratory-made electrospray ionization (ESI) interface. For the effective ionization of 2,4-DCP at the
A fast method for the generation of permanent hydrophilic capillary coatings for capillary electrophoresis (CE) is presented. Such interior coating is effected by treating the surface to be coated with a solution of glutaraldehyde as cross-linking agent followed by a solution of poly(vinyl alcohol) (PVA), which results in an immobilization of the polymer on the capillary surface. Applied for capillary zone electrophoresis (CZE) such capillaries coated with cross-linked PVA exhibit excellent separation performance of adsorptive analytes like basic proteins due to the reduction of analyte-wall interactions. The long-term stability of cross-linked PVA coatings could be proved in very long series of CZE separations. More than 1000 repetitive CE separations of basic proteins were performed with stable absolute migration times relative standard deviation (RSD > 1.2%) and without loss of separation efficiency. Cross-linked PVA coatings exhibit a suppressed electroosmotic flow and excellent stability over a wide pH range.
Polycyclic aromatic hydrocarbons (PAHs) are widely distributed and relocated in the environment as a result of the incomplete combustion of organic matter. Many PAHs and their epoxides are highly toxic, mutagenic and/or carcinogenic to microorganisms as well as to higher systems including humans. Although various physicochemical methods have been used to remove these compounds from our environment, they have many limitations. Xenobiotic-degrading microorganisms have tremendous potential for bioremediation but new modifications are required to make such microorganisms effective and efficient in removing these compounds, which were once thought to be recalcitrant. Metabolic engineering might help to improve the efficiency of degradation of toxic compounds by microorganisms. However, efficiency of naturally occurring microorganisms for field bioremediation could be significantly improved by optimizing certain factors such as bioavailability, adsorption and mass transfer. Chemotaxis could also have an important role in enhancing biodegradation of pollutants. Here, we discuss the problems of PAH pollution and PAH degradation, and relevant bioremediation efforts.
The influence of three univalent salts (LiCl, NaCl and RbCl) on the separation of amino acids labelled with 3-(4-carboxybenzoyl)-quinoline-2-carboxaldehyde (CBQCA) in micellar capillary electrophoresis has been studied. Capacity factors for a series of eight CBQCA-labelled amino acids in a sodium dodecyl sulfate (SDS) micellar system containing different concentrations of salt were measured and were found to be related to both the hydrodynamic radius of the salt counter-ion (Li(+), Na(+), Rb(+)) and the relative hydrophobicity of the amino acid. Affinities of the analytes for the micelles were generally observed to decrease as the salt concentration in the background electrolyte was increased from 10 to 50 mM. This decrease in affinity was greatest in the presence of the salt counter-ion with the smallest hydrodynamic radius and is primarily due to an increased resistance to mass transfer. Furthermore, interaction of hydrophobic analytes with the micelles is greater than that of hydrophilic analytes at all salt concentrations due to the greater strength of the hydrophobic interactions and this effect is also enhanced in the presence of a smaller counter-ion. No negative effects due to Joule heating or electromigrative dispersion were observed for low to moderate concentrations of salt, which suggests that the use of simple univalent salts to modify analyte/micelle affinities can be a practical method for improving the separation of complex mixtures.
The potential of titanium dioxide coatings to control the electroosmotic flow and to affect the migration behavior of analytes in capillary electrophoresis and open-tubular capillary electrochromatography was evaluated. The inner wall of a fused-silica capillary was applied with a solution of a titanium peroxo complex, followed by heating at an elevated temperature. The resultant product was ascertained to be titanium dioxide in a crystalline form of anatase by the results of Fourier transform-infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy, and Raman spectroscopy. The capillary thus made had anodic or cathodic electroosmotic flow, depending on the pH and composition of the background electrolyte used. The titanium dioxide surface of the capillary was readily modified by a silanizing reagent. The performance of the titanium dioxide surfaces with or without chemical modifications was examined with inorganic anions, neutral compounds and peptides.
The focus of this article is amperometric and voltammetric detection coupled with capillary electrophoresis. Fundamental concepts and progress in the field of capillary electrophoresis with electrochemical detection (CEEC) that have occurred within the past three years, including new methodologies and unique applications, are highlighted. This review contains 95 references.
Phenolic compounds were analyzed by means of capillary electrophoresis with chemiluminescence detection. Peroxyoxalate chemiluminescence reagent was used together with dansyl chloride as a labeling reagent. The reagent concentrations, the labeling procedures, and the performance of chemiluminescence detection cells were examined for sensitive detection of phenolic compounds. Six kinds of phenolic compounds (phenol, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, and 2,4,6-trichlorophenol) were determined over a range of three orders of magnitude with detection limits of the order of 10(-7) M; their detection limits were ca. 10 times as low as those obtained by an ordinary fluorescence detector. A running buffer solution containing sodium dodecylsulfate and acetonitrile provided satisfactory results in the separation of 15 kinds of phenolic compounds. The combination of capillary electrophoresis with chemiluminescence detection and column concentration procedure supported the possibility that the present system could be applied to real samples such as surface and reused waters.
A convenient method for the GC determination of phenols as methylated derivatives is proposed, taking advantage of the beneficial features of phase-transfer catalysis (PTC). The optimal experimental conditions of pH, temperature, organic solvent, time of extraction-derivatization and amounts of the participating reactants and catalysts, were properly established. Several catalysts in soluble or polymer-bound form were tested. Most of them demonstrated appreciably high-performance characteristics but the polymer-bound catalyst is most favourable due to its facile separation from the rest of the reaction system after the extraction-derivatization. Interferences with the extraction and derivatization yield were not noticed. The chromatographic separation of 11 methylated derivatives of phenols was complete within 23 min. The detection limits of the method, which range from 0.005 to 0.120 microg, are inadequate for drinking water analysis. However, the method was successfully applied to the analysis of fortified composite lake water samples using GC-flame ionization detection and GC-MS in the single ion monitoring mode with the most abundant characteristic ions. Spiked recoveries of phenolics were in the range 94-102%, on the basis of distilled water calibration graph, signifying that PTC determination of phenols is not affected by the composition of such matrices.
Benzophenones are common additives in commercial sunscreen products. These UV absorbers were extracted by supercritical fluid extraction (SFE), and then analyzed by capillary zone electrophoresis (CZE) and high-performance liquid chromatography. This study was applied to identify the contents of benzophenones in cosmetic matrix, and simultaneously, to investigate the behavior of migration in CZE. Adding non-ionic surfactant (Tween 20) to optimize the separation in the CZE operation improves resolution. In SFE, we chose carbon dioxide with 2.5% modifier of 10% aqueous phosphoric acid-MeOH (1:1) as the supercritical fluid. Real recoveries of up to 92% with relative standard deviations of less than 4.0% were achieved. These analytical techniques were also applied to assay benzophenones for ten commercial sunscreen cosmetics. We found benzophenone 3 was the most commonly used sunscreen additive in Taiwan.
We have developed a strategy using ultraviolet light to polymerize mixed monomer solutions onto the surface of a poly(dimethylsiloxane) (PDMS) microdevice. By including monomers with different chemical properties, electrophoretic separations were optimized for a test set of analytes. The properties of surfaces grafted with a single neutral monomer, a neutral and a negative monomer, or a neutral, negative, and cross-linking monomer were assessed. The highest quality separations were achieved in channels with cross-linked coatings. The separation efficiency for biologically relevant peptides (kinase substrates) on these surfaces was as high as 18 600 theoretical plates in a 2.5 cm channel. The test peptides were fluorescein-AEEEIYGEFEAKKKK, fluorescein-GRPRAATFAEG, fluorescein-GRPRAA(T-PO(3))FAEG, fluorescein-DLDVPIP GRFDRRVSVAAE, and fluorescein-DLDVPIPGRFDRRV(S-PO(3))VAAE. Separations between two different peptides occurred in as little as 400 ms after injection into the separation channel. The simultaneous separation of five kinase and phosphatase substrates was also demonstrated. By carefully selecting mixtures of monomers with the appropriate properties, it may be possible to tailor the surface of PDMS for a large number of different electrophoretic separations.
Mixtures of the cationic surfactant cetyltrimethylammonium bromide (CTAB) with the anionic surfactant sodium dodecyl sulfate (SDS) form more stable coatings in fused-silica capillaries than CTAB alone. The reversed electroosmotic flow (EOF) generated by CTAB/SDS mixtures remains stable for over 80 min after removal of the surfactants from the buffer. Enhanced stability (relative to CTAB alone) was found even when the ratio of SDS to CTAB was as low as 1%. This greater coating stability is attributed to the structural transition from adsorbed micelle to bilayer, which is induced by addition of SDS. Separation of a mixture of basic proteins yielded efficiencies of 364 000-562 000 plates/m and recoveries ranging from 85% to 98%. Migration time reproducibility was less than 0.9% relative standard deviation (RSD) from run to run and less than 2.6% RSD from day to day.