Dual-electrode amperometric detectors

The use of dual-electrode amperometric detectors provides advantages in sensitivity and detection limits. Series configuration and parallel configuration are both possible. Ion-selective electrodes allow the selective quantification of selected analytes even in complex matrices. 

J.A. Stenken, D.L. Puckett, S.M. Lunte and C.E. Lunte, Detection of A -acetylcysteine, cysteine and their disulfides in urine by liquid chromatography with a dual-electrode amperometric detector, J. Pharm. Biomed. Anal, 1990, 8, 85-89. 

Z Liu, T Li, J Li, E Wang. Detection of menadione sodium bisulfite (vitamin Kj) by reversed-phase high performance liquid chromatography with series dual-electrode amperometric detector. Anal Chim Acta 338 57-62, 1997. 

FIGURE 3-26 Dual-electrode thin-layer detector configurations for operation in the series (a) and parallel (b) amperometric modes. 

The electronic tongue system based on flow injection analysis (FIA) with two amperometric detectors was set up. The FLA apparatus consisted of a Jasco (Tokyo, Japan) model 880 PU pump and two EG G Princeton Applied Research (Princeton, NJ, USA) Model 400 thin-layer electrochemical detector connected in series. Each detector was equipped with a working electrode (a dual glassy carbon electrode and a gold... 

A unique voltammetric detector has been developed using a series dual-electrode cell. In the detector, the upstream electrode s potential is scanned while the downstream electrode is used to monitor the redox reaction occurring at the upstream electrode without the charging current contributions. In essence, the upstream electrode is operated voltammetrically and the downstream electrode operated amperometrically so that the detector has been named a voltammetric-amperometiic detector. Detection limits of 10 M have been reported using this detection scheme. 

Phenol and the three dihydroxybenzenes (20, 42, 66) in water were determined by LLE with a hydrophilic solvent followed by amperometric titration. LOD was in the ppm range . A dual electrode in a FIA system has been used as detector for total phenols in wastewater. The upstream coulometric electrode has a large surface area and is used to eliminate compounds that cause interference and the second one is an amperometric electrode for oxidative detection of all phenols. Optimal results were found working with a phosphate buffer at pH 6.8, at potentials of +0.35 V and +0.78 V for the coulometric and amperometric electrodes, respectively. A high sample throughput of 60 per hour can be attained with RSD of 0.1-4%. This method is more reliable than the colorimetric method . The concentration of fenobucarb (142) in drinking water was determined after a short alkaline hydrolysis, and oxidation of the resulting 2-s-butylphenol with a GCE at 750 mV, pH 3.5 LOD was 3.6 x 1Q- M, RSD 3.74% for 1 x IQ- M (n = 11, p = 0.05)37 . 

TL, thin-layer cell equipped with a glassy carbon electrode WJ, wall-jet cell equipped with a glassy carbon electrode CO-screen coulometric cell with dual-electrodes of porous graphite used in screen mode PAD, pulsed amperometric detector equipped with a gold electrode. 

One such technique that has been shown to both improve the selectivity and sensitivity is that of the dual electrode electrochemical detection (DED). There are two different types of dual electrode detector systems in series, or in parallel. Further modification of these terms is gained by the application of either amperometric or coulometric electrodes. 

Aniline, methyl aniline, 1-naphthylamine, and diphenylamine at trace levels were determined using this technique and electrochemical detection. Two electrochemical detectors (a thin-layer, dual glassy-carbon electrode cell and a dual porous electrode system) were compared. The electrochemical behavior of the compounds was investigated using hydrodynamic and cyclic voltammetry. Detection limits of 15 and 1.5nmol/l were achieved using colourimetric and amperometric cells, respectively, when using an in-line preconcentration step. 

Using a packed bed of Hg-coated Ag particles approximately the size of a precolumn, Eggli and Asper (1978) developed a novel scheme for the detection of thiols and disulfides. The packed reactor was inserted between the column and an amperometric Hg pool electrode detector. Incoming disulfides were effectively reduced in the reactor to the parent thiol, followed by the latter s downstream detection at the Hg pool, llie approach was considerably miniaturized using a dual Hg/Au thin-layer cell, with concomitant improvement in SNR (Allison and Shoup, 1983). 

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