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Schemes of tested amperometric detectors.: A) Thin-layer detector: auxiliary electrode: stainless steel block with cross-flow pattern (1), inlet (2), outlet (3), reference argent chloride electrode (4); working electrode: silver solid amalgam and stainless steel cord as contact (5), Teflon body of working electrode with steel cover for quick release (6), cross-flow cell gasket (7), quick release (8). B) Wall-jet detector: reference AgCl electrode (1); working electrode: polished silver solid amalgam electrode (2), silver solid amalgam (3); platinum wire auxiliary electrode (4), overflow whole-glass vessel (5), inlet (6), outlet (7).
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The use of a silver solid amalgam working electrode for HPLC with electrochemical detection has been investigated. The thin-layer and wall-jet detectors based on this electrode were constructed and applied for the determination of a mixture of nitrophenols. The optimal separation and detection conditions for the determination of 2-nitrophenol, 4-ni...
Contexts in source publication
Context 1
... wall-jet detector consisted of a three electrode system: a silver chloride reference electrode (Ag j AgCl, 3 M KCl, type 10 -20 þ, Elektrochemicke Detektory, Turn- ov, Czech Republic), a platinum wire auxiliary electrode (Monokrystaly, Turnov, Czech Republic) and a polished silver solid amalgam working electrode (p-AgSAE, diam- eter 2.98 mm in glass tube) adjusted against the capillary outlet at a controlled distance, all imbedded in the overflow whole-glass vessel. Scheme of both arrangements is shown in Figure 1. These detectors were operated by electrochemical ana- lyzer (CHI 6012B, CH Instruments, USA) controlled by software CHI Version 6.10 (CH Instruments, USA) working under the operation system Windows XP (Microsoft, USA). ...
Context 2
... 5-NG) at HMDE [16] and at AgSAE [17] have been already described. Nitrophenols (NPs) and substituted NPs are frequently used in industry (drugs, dyes) and agriculture. They are listed by US Environmental Protection Agency (EPA) on the List of Priority Pollutants [18] and thus they are frequently determined by various separation techniques [19 – 21]. The agrochemicals Atonik or Chaperone (Asahi Co., Japan), Litosen (Forward Int., China) or N-Fenol MIX (AGRA Group, Czech Rep.) are world wide used plant growth regulators increasing shoot- ing, rooting, growth of plant and pest immunity [22, 23]. These agrochemicals are a special mixture of nitrophenol sodium salts and beside bioregulation attributes they stimulate all biochemical and physiological processes in plants and mobilize plants bioenergetics reserves [24]. N- Fenol MIX (NFM) contains concentrated mixture of 2-NP, 4-NP, DNP and 5-NG sodium salts. It is similar to a three component agent Atonic not containing DNP. NFM was used as real sample for testing the developed method using HPLC-ED based on AgSAE. Thin-layer LC-EC Flow Cell (BASi, USA) was used. The cell is commercially available in many arrangements depending on flow patterns (cell gasket) and constitution of auxiliary and working electrodes (based on glassy carbon or pure metal, i.e. copper, gold, silver, nickel or platinum) [25]. The flow cell used in this work was composed of auxiliary electrode (stainless steel block with cross-flow pattern (MF-1092, BASi, USA) with cross-flow cell gasket 0.002“ thick (polyethylene, MF-1046, BASi, USA), reference electrode (Ag j AgCl (KCl sat ), MF-2021, BASi, USA) and working AgSAE. AgSAE for this thin-layer detector was designed according to commercial glassy carbon electrode (BASi, USA) and produced by Science workshops at Hong Kong Baptist University. It contained a cylinder of silver solid amalgam (AgSA, diameter 3 mm) embedded in a Teflon block with steel cover for quick release and contact made from stainless steel cord. The AgSA was prepared from silver metal powder (Ag, 2 – 3.5 m m, 99.9 þ %, Aldrich, Germany) stuffed in to the Teflon block and the metal mercury (polarographic purity), which was added in several parts until mercury made a mirror on the amalgam surface. Silver amalgam was left to harden overnight and polished by alumina (Al 2 O 3 , 0.03 m m, ! 99%, Aldrich, Germany) on the wet velvet pad and activated in KCl solution (0.2 mol L À 1 ) by imposed potential À 2.2 V for 5 min. The final calculated silver content in thus prepared amalgam was about 18% Ag (w/w). The wall-jet detector consisted of a three electrode system: a silver chloride reference electrode (Ag j AgCl, 3 M KCl, type 10 – 20 þ , Elektrochemicke Detektory, Turnov, Czech Republic), a platinum wire auxiliary electrode (Monokrystaly, Turnov, Czech Republic) and a polished silver solid amalgam working electrode (p-AgSAE, diameter 2.98 mm in glass tube) adjusted against the capillary outlet at a controlled distance, all imbedded in the overflow whole-glass vessel. Scheme of both arrangements is shown in Figure 1. These detectors were operated by electrochemical ana- lyzer (CHI 6012B, CH Instruments, USA) controlled by software CHI Version 6.10 (CH Instruments, USA) working under the operation system Windows XP (Microsoft, USA). Tests of working electrodes were realized by batch measurements using direct current voltammetry (DCV) and differ- ence pulse voltammetry (DPV). The chromatograms were registered as amperometric I – t curves at set potential with sample period 0.2 s. The newly constructed detectors were connected to conventional HPLC systems consisting of an isocratic HPLC pump WATERS 510 (Millipore, USA), an injector WATERS U6K (Millipore, USA) with manual injection of specific volume by Hamilton syringe (max. 50 m L, Hamilton Co, USA), and an RP-HPLC column Nova-Pack C18, 3.9 Â 150 mm (Waters, Ireland). 2-Nitrophenol (99%, 2-NP), 4-nitrophenol (98%, 4-NP), 2,4-dinitrophenol (97%, DNP), 2-methoxy-5-nitrophenol (5-nitroguaiacol, 98%, 5-NG) were purchased from Aldrich (Germany) and their 1 Â 10 À 3 mol L À 1 stock solutions were prepared by dissolution of exactly weighted amounts of pure substances in water or in 50% methanol (for 2-NP). These stock solutions and real sample of NFM, obtained from AGRA Group, Czech Republic, were stored in dark in refrigerator. More diluted solutions were prepared by exact dilution with water or with 50% MeOH (for ...
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Citations
... Although the use of liquid mercury in electroanalytical techniques, such as polarography [1][2][3][4] and voltammetry [5][6][7], has a justified tradition, the fear of mercury toxicity and related diseases [8] lead to the search for new electrode materials [9]. Conventional types of electrodes, such as a dropping mercury electrode and a hanging mercury drop electrode, can be successfully substituted by electrodes containing small amounts of liquid mercury or non-toxic mercury amalgams [10,11] (e.g., polished [12][13][14], mercury meniscus modified [12,13,15,16], mercury film modified [12,17], bismuth film modified [18,19], or carbon film modified silver solid amalgam electrodes [20][21][22], silver solid amalgam paste electrodes with an organic pasting liquid [23,24], silver amalgam paste electrodes [25,26], polished silver solid amalgam composite electrodes [27,28], single crystal amalgam electrodes [29,30], or renewable silver amalgam film electrodes [31,32]). Novel silver amalgam-based electrode materials combine unrivalled properties of mercury electrodes (broad cathodic potential window and relatively high sensitivity [33][34][35]) with requirements of Green Analytical Chemistry (GAC) (non-toxicity and environmental friendliness [36]). ...
A silver solid amalgam electrode modified with mercury meniscus (m-AgSAE) was used as a non-toxic replacement of mercury electrodes in the voltammetric determination of genotoxic environmental pollutant 4-nitroindane (4-NI). The m-AgSAE was used to characterize of the overall electrode process during the 4-NI conversion using cyclic voltammetry (CV), and it was shown that the electrochemical reduction of 4-NI is an irreversible process controlled by both diffusion and adsorption. Techniques of direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at the m-AgSAE were optimized for the development of a method for the sensitive determination of 4-NI. The application of the more convenient DPV method was proven on authentic drinking and river water samples. Limits of quantification (LQs) obtained under the following optimal conditions were 0.1 µmol L−1 for DCV at the m-AgSAE (BR buffer pH 5.0-methanol (1:1); regeneration potentials E1,reg = −200 mV, E2,reg = −1100 mV) and 0.1 µmol L−1 for DPV at the m-AgSAE (BR buffer pH 9.0-methanol (1:1); regeneration potentials E1,reg = −300 mV, E2,reg = −1300 mV). An attempt to decrease the LQ of the 4-NI determination by differential pulse adsorptive stripping voltammetry at the m-AgSAE was not successful. The LQs for DPV at the m-AgSAE in authentic samples of drinking and river water were 1.0 µmol L−1 and 2.0 µmol L−1 (BR buffer pH 9.0-drinking or river water (1:9); regeneration potentials E1,reg = −300 mV, E2,reg = −1300 mV), respectively.
... Amalgam electrodes have a high hydrogen overvoltage in aqueous solutions and are practically the only electrodes suitable for reliable work in flow systems at potentials more negative than − 1.1 -− 1.2 V [29]. Silver amalgam electrodes were prepared in the laboratory of our research group and used for different flow cell designs: wall-jet [18,26,28,30,31], thin-layer [30], flowthrough with tubular detector [22][23][24][25]28,[32][33][34] and for the cell with printed electrodes [14,35]. The design of the wall-jet cell for printed electrodes allows a thin disc of suitable filter material with immobilized enzyme to be placed directly at the electrode. ...
... Amalgam electrodes have a high hydrogen overvoltage in aqueous solutions and are practically the only electrodes suitable for reliable work in flow systems at potentials more negative than − 1.1 -− 1.2 V [29]. Silver amalgam electrodes were prepared in the laboratory of our research group and used for different flow cell designs: wall-jet [18,26,28,30,31], thin-layer [30], flowthrough with tubular detector [22][23][24][25]28,[32][33][34] and for the cell with printed electrodes [14,35]. The design of the wall-jet cell for printed electrodes allows a thin disc of suitable filter material with immobilized enzyme to be placed directly at the electrode. ...
https://authors.elsevier.com/c/1ibjZ5aQisYVZy - a link providing free access to the article until April 05, 2024
... At present, the methods for p-NP detection include spectrophotometry, capillary electrophoresis, high performance liquid chromatography, Raman spectroscopy, etc. (Niazi and Yazdanipour, 2007;Qiu et al., 2007;Danhel et al., 2009;Iqbal, 2011;Vijayarangamuthu and Rath, 2014;Menazea and Mostafa, 2020) However, these strategies often suffer from the problems of complex detection process, high cost, and slow speed. Electrochemical methods have the advantages of rapid detection, low cost, simple instrumentation, easy integration, and suitability for miniaturization. ...
Convenient, rapid and sensitive detection of p-nitrophenol (p-NP), one of the priority environmental pollutants, in environmental samples is of great significance. Electrochemical sensor with simple fabrication process, high sensitivity and selectivity, good antifouling, and regeneration performance is highly desirable. Herein, an electrochemical sensing platform is demonstrated based on the integration of vertically-ordered mesoporous silica-nanochannel film (VMSF) on electrochemical pre-activated glassy carbon electrode (p-GCE), which is able to realize ultrasensitive detection of p-NP in environmental samples. Electrochemical pre-activation of GCE is achieved through a simple and green electrochemical polarization process including anodic oxidation at high voltage and the following cathodic reduction at low voltage. The p-GCE possesses enhanced active area and introduced active sites, and enables stable binding of VMSF. VMSF is easily grown on p-GCE through the electrochemically assisted self-assembly (EASA) method within 10 s. Owing to the hydrogen bonding between silanol groups and p-NP, VMSF nanochannels display strong enrichment effect for the detection of p-NP. The developed VMSF/p-GCE sensor can achieve sensitive detection of p-NP ranging from 10 nM to 1 μM and from 1 to 30 μM with a limit of detection (LOD) of 9.4 nM. Considering the antifouling ability of VMSF, detection of p-NP in pond water is achieved.
... Nitrophenols are easily electrochemically oxidizable and reducible as proved by comparative electrochemical study of 4-NP at a glassy carbon electrode (GCE) [8]. Modern voltammetric methods have been already used for voltammetric determinations of several nitrophenols at a silver solid amalgam electrode [4,9], a silver amalgam paste electrode [10], a boron-doped diamond film electrode [11], a bismuth film modified screen-printed carbon electrode [12], a hanging mercury drop electrode [13], and a carbon film electrode [14]. Differential pulse voltammetry (DPV) at a highly dispersed silver particles modified GCE [15], square-wave voltammetry and amperometry at a bismuth film modified GCE [16], or single-walled carbon nanotubes based sensor [17] were applied for monitoring of nitrophenols as well. ...
A new method was developed for the determination of 2-nitrophenol (2-NP) by differential pulse voltammetry (DPV) employing the anodic oxidation of the present hydroxyl group using a non-traditional carbon film composite electrode (CFCE) based on a microcrystalline natural graphite-polystyrene composite film. Britton-Robinson (BR) buffer of pH 6.0 was found to be an optimal supporting electrolyte. Cleaning regeneration potentials Ein = +1300 mV and Efin = 0 mV had to be applied before each measurement to get rid of problems connected with electrode passivation. Linear calibration curves were obtained in the concentration range from 0.2 to 10 µmol L-1 of 2-NP for both tested matrices (deionized and drinking water). Limit of quantification (LOQ) for DPV at the CFCE was found to be 0.2 µmol L-1 and 0.1 µmol L-1 for deionized and drinking water, respectively.
... However, there were few reports about the detection of 5-NG in the Web of Science. Traditional methods like high-performance liquid chromatography (HPLC) combining atmospheric pressure chemical ionization coupled with mass spectrometry (Xing et al., 2016) and HPLC with electrochemical detection (Danhel et al., 2009) were used for the detection of 5-NG. Although these methods are accurate in real samples, they also suffer from some drawbacks such as time-consuming, necessary expensive equipment and complicated sample preparation, weak anti-interference ability, etc. ...
... By calculation, the LOD and LOQ were 0.02 μM and 0.067 μM, respectively. In comparison with the previous reports for the detection of 5-NG (Xing et al., 2016, Danhel et al., 2009), the proposed method had a lower LOD and wider linear range, indicating that MoS 2 -COOH-MWCNT nanohybrid as the nanozyme for the detection of 5-NG had good sensing performance. The repeatability of MoS 2 -COOH-MWCNT/GCE for voltammetric responses of 5-NG was studied by twenty successive measurements by DPV in buffer solution (pH = 4) (Fig. 7a). ...
A nanozyme sensor consisted of both carbonylated multi-walled carbon nanotubes (COOH-MWCNT) and two-dimensional layered molybdenum disulfide (MoS2) nanosheets for the sensitive detection of 5-nitroguaiacol sodium (5-NG) in tomato and broiler feed under the optimal conditions was successfully developed. MoS2-COOH-MWCNT nanohybrid was simply obtained by ultrasonic preparation in presence of Nafion. The MoS2-COOH-MWCNT film was characterized, and parameters of their film electrodes such as pH, scan rates, the percentage content of Nafion (Nf), and the ratio between COOH-MWCNT and MoS2 were optimized. The MoS2-COOH-MWCNT nanohybrid was used to detect 5-NG in tomato and broiler feed, and their recoveries were 102.22 and 93.2%, respectively. The electrocatalytic oxidation mechanism of 5-NG and oxidase-like (nanozyme) kinetics of MoS2-COOH-MWCNT nanohybrid were investigated. The fabricated nanozyme sensor displayed good electrochemical responses, wide linear ranges of 0.1–70 μM with limit of detection (LOD) 0.02 μM, unique oxidase-like characteristics, and good practicability, which will provide a new sensing platform based on inorganic nanomaterials with enzyme-like (nanozyme) characteristics for the determination of 5-NG in plant-derived agro-products and/or plant-derived animal feeds.
... Hence, the determination of 2-NP has been a new trend of modern research. However, there are some methods for the detection of 2-NP, for instance, RP LC DAD, HPLC, LC MS, and LC MS/MS [5][6][7][8] . Though, the methods are not economical and effective. ...
The Rationally designed and functional electronic-structures of TMOs (precisely: Copper and Manganese) beside purposeful morphologies were prepared over modest a facile synthetic method. The physical, chemical, and crystalline characters of TMOs were scrutinized over FE-SEM, HRTEM, XRD, and Raman spectroscopic analysis; conclusively. The prepared microstructures of TMOs@RGO such as RGO@CuO@Mn2O3, CuO nanoparticles (NPs), and Mn2O3 ¬nanosheet (NSs), and rGO were examined for the quantification of 2-nitrophenol (2-NP), to evaluate the electrocatalytic ability of TMOs@RGO towards electrochemical biosensing. Beneath the satisfactory optimization, the fine reduction peak was obtained at RGO@CuO@Mn2O3/GCE stating the sensing of 2-NP, by holding the linear range of 0.5 - 126 µM, and the LOD of 0.021 µM. The applicability of the established sensor was tested on the river water and lake water, whereas the significant spike recoveries were gotten similarly.
... Herein utilized double pulse potentiostatic chronoamperometry (DPCA) was optimized towards a suitable electrochemical response for a model organic nitro compound, 4-nitrophenol (4-NP). Its sodium salt is widely used as a drug, colorant or component of various agrochemicals worldwide (Atonic ® , N-phenol MIX ® etc.) [29], even though 4-NP is registered by the US Environmental Protection Agency on the List of Priority Pollutants [30,31]. vAuE's morphological changes upon AgAPs' (vAuE-AgAP) deposition during DPCA optimization were observed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). ...
Alternative electrode materials suitable to prepare novel working electrode applicable in detecting biopolymers such as nucleic acids, proteins or glycoproteins, represent a significant contribution to bio‐electroanalysis. Herein, electrodes made of vapor‐deposited thin gold films (vAuE) were used as an alternative substrate for the electrodeposition of silver amalgam particles (AgAPs), next to indium tin oxide and pyrolytic graphite, which are already used. The conditions and parameters of double pulse chronoamperometry were optimized for the most‐sensitive voltammetric detection of 4‐nitrophenol (4‐NP). The resulting electrodes were characterized by scanning electron microscope with energy dispersive X‐ray spectroscopy. While 4‐NP could not be detected by bare nonactivated vAuEs at all, their electrochemical activation offered a limit of detection (LoD) of 25 and 5 μmol.l−1 by means of CV and DPV, respectively. AgAP electrodeposited on vAuE, offered 2.5‐times lower LoDs 10 μmol.l−1 by CV and comparable LoD 5 μmol.l−1 by DPV. Advantageously, AgAPs could be repeatedly deposited on and anodically dissolved from the vAuE with a relative standard deviation 13 % of the ten‐times repeated DPV signal of 4‐NP (100 μmol.l−1). In comparison to vAuE, the vAuE‐AgAP offered about 400 mV broader potential window, which allowed detection of single strand DNA fragment labeled by osmium tetroxide−bipyridine complex down to 2 ng.μl−1 by means of DPV.
... With spectrophotometric detection, it is cost effective even in the developing world [3]. Compared with spectrophotometry, electrochemical detection coupled with HPLC affords very low detection limits in the analyses of electroactive compounds such as various biomarkers, vitamins, polyphenols, saccharides, drugs etc. with particular interest in medical diagnosis and various sectors of industrial and environmental analysis [4][5][6][7]. ...
A concentric thin layer cell accommodating a non-standard 0.2 mm diameter pencil graphite disposable working electrode is described. The cell was installed into HPLC manifold as an electrochemical detector. Trouble-free operation in mobile phases containing both low and high content of organic solvents is demonstrated by HPLC analyses of phenolic acids and tocopherol isomers. The data obtained from HPLC separation of model mixtures of gentisic, caffeic and dihydrocaffeic acids show a remarkable electrolytic efficiency exceeding 80% at 200, and 50% at 500 μL min⁻¹, while for gentisic acid the limit of detection (LOD) was 0.4 nmol L⁻¹ at 20 microliter sample loading (8 fmol on-column). Similar performances were found in non-aqueous mobile phase, where a LOD of 0.8 nmol L⁻¹ was achieved for delta-tocopherol. The developed flow-through detector is designed to allow easy replacement of pencil graphite working electrode in a highly reproducible manner. The relative standard deviation for the HPLC analysis of tocopherol isomers was of 5.3% (n = 3, C = 500 nmol L⁻¹). The combination of simple construction, excellent electrochemical performance and hydrodynamics identical to that of commercial UV-VIS HPLC detector suggests that the proposed device is a viable low-cost alternative to commercially available electrochemical detectors.
... However, there is still a great potential to connect advantages of the metallic mercury and bimetallic colloids/nanoparticles in electrochemical and furthermore in spectroscopic applications [10,11]. All of the so far designed AgSA based electrodes (AgSAE), (bio)sensors [12][13][14][15] and (bio)reactors [16,17] have been prepared by direct dispersion of silver powder in liquid mercury in a suitable ratio or by electrodeposition of mercury film on silver or AgSA supports [18][19][20]. Unfortunately, lower homogeneity and charge transfer efficiency of AgSAE in comparison with mercury or nanomaterial-based electrodes, limits its common utilization [21,22]. ...
Silver solid amalgam represents up to now the most suitable alternative electrode material to metallic mercury in electroanalytical chemistry. Controlled electrodeposition of variable (sub)micrometer-sized silver amalgam particles (AgAP) on the surface of transparent indium-tin oxide (ITO) electrode from an electrolyte containing Ag⁺ and Hg²⁺ ions is reported here, as a novel perspective method suitable for preparation of nano-structured silver amalgam electrode material. Elemental analysis of the composition and morphology of the AgAP decorating the ITO was studied by scanning electron microscopy including energy-disperse X-ray spectroscopy and by image processing software. Particle composition, size, and surface coverage are controllable by selection of the Ag⁺/Hg²⁺ ratio in the electrodeposition solution and by setting of individual parameters of applied double pulsed/potential chronoamperometry. Applicable potential window of thus prepared ITO-AgAP electrode was found to be within +0.2 to -1.0V in 0.2acetate buffer pH5.0. Utilized voltammetric and chronoamperometric methods revealed significant enhancement in electrochemical reducibility of selected model organic nitro-compound (shift of the peak potential about 300mV to more positive potentials). Its further employment in UV/Vis spectroelectrochemical cell provided information about number of consumed electrons and kinetic characteristics. Furthermore preferential adsorption of calf thymus DNA at AgAP than ITO was observed by fluorescence microscopy indicating its potential applicability in (bio-)spectroelectrochemical methods. Further advantages and potential applications are also proposed and discussed.
... Nevertheless, the potential risks of 82 poisoning, contamination and disposal connected with the use of mercury, together with 83 the toxicity of its inorganic salts and organic compounds, have led some countries to 84 ban its use or to strictly regulate it [15]. With that in mind, a lot of effort was put into 85 the development of solid electrodes (e.g., solid amalgam electrodes [16,17], carbon 86 paste electrodes [18] or boron-doped diamond electrodes [19]) as non-toxic alternatives 87 for classical mercury electrodes. The advantages of solid amalgam electrodes include: a 88 wide range of working potentials, mechanical stability, simple handling, simple 89 regeneration of the electrode surface, long-term activity and low toxicity [20][21][22]. ...
A new approach was developed for the determination of trace amounts of diacetyl in food products using gas-diffusion microextraction (GDME) and subsequent detection by differential pulse voltammetry (DPV) at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE). Diacetyl is a vicinal diketone responsible for the buttery aroma in many fermented foods and beverages. Its determination is important not only for evaluation of the final product quality (note of mention: health related concerns were associated with continuous diacetyl exposure) but also to monitor fermentation. GDME, a technique combining gas-diffusion and microextraction, particularly aimed to volatile and semi-volatile analytes, seemed the best way to selective extract diacetyl. A solution of 0.05% o-phenylenediamine (OPDA) prepared in a Britton-Robinson buffer (pH 5.0) was chosen as the extracting solution. This solution simultaneously extracts, pre-concentrates and derivatizes diacetyl to 2,3-dimethylquinoxaline (DMQ), enhancing the extraction selectivity and making the analyte electroactive. After finding the optimum conditions for the extraction process (10 min at 60 °C with 1.0 mL of OPDA at pH 5.0), the DPV measurements at the m-AgSAE were conducted with a scan rate of 7 mV s-1, a modulation amplitude of 50 mV and a modulation time of 100 ms. Under these conditions, the resulting DMQ could be easily measured at a potential of -0.6 V vs. Ag|AgCl (3 mol L-1 KCl). The amalgam electrode keeps the advantages of classic mercury electrodes, like high sensitivity, while being environmentally friendly. The GDME/m-AgSAE produced suitable method features for the determination of low amounts of diacetyl (as DMQ) in alcoholic beverages, and in fact, to the best of our knowledge, the limit of quantification of 0.18 µg L-1 is one of the lowest reported in literature.
