Amperometric flow-injection detector

Solvent Extraction Using a Polymer as Solvent with an Amperometric Flow-Injection Detector... 

H. Ma, L. Jin, and H. Yan, Flow Injection Analysis of Traces of Free Cyanide in Surface and Ground Waters with an Amperometric Flow-Through Detector [in Chinese]. Kexue Tongbao, 28 (1983) 1145. 

Rippeth J. J., Gibson T. D., Hart J. R, Hartley I. C., and Nelson G., Flow-injection detector, incorporating a screen-printed disposable amperometric biosensor for monitoring organophosphate pesticides. Analyst., 122, 1425-1429,1997. 

Electrochemical Detectors Another common group of HPLC detectors are those based on electrochemical measurements such as amperometry, voltammetry, coulometry, and conductivity. Figure 12.29b, for example, shows an amperometric flow cell. Effluent from the column passes over the working electrode, which is held at a potential favorable for oxidizing or reducing the analytes. The potential is held constant relative to a downstream reference electrode, and the current flowing between the working and auxiliary electrodes is measured. Detection limits for amperometric electrochemical detection are 10 pg-1 ng of injected analyte. 

Enzyme linked electrochemical techniques can be carried out in two basic manners. In the first approach the enzyme is immobilized at the electrode. A second approach is to use a hydrodynamic technique, such as flow injection analysis (FIAEC) or liquid chromatography (LCEC), with the enzyme reaction being either off-line or on-line in a reactor prior to the amperometric detector. Hydrodynamic techniques provide a convenient and efficient method for transporting and mixing the substrate and enzyme, subsequent transport of product to the electrode, and rapid sample turnaround. The kinetics of the enzyme system can also be readily studied using hydrodynamic techniques. Immobilizing the enzyme at the electrode provides a simple system which is amenable to in vivo analysis. 

Because of its advantages (high sensitivity and selectivity, low cost and miniaturization) amperometric detection has been frequently used in flow injection analysis (FIA) and RP-HPLC. However, it has been established that the peak area (detector response) considerably depends on the flow rate. A general approach has been proposed to predict the effect of flow rate on the peak area in FIA and RP-HPLC. The general form of the correlation describing the flow in a parallel plate cell with short rectangular electrodes is... 

Cosio et al. (2006) used an electronic tongue system based on flow injection analysis (FIA) with two amperometric detectors, together with the use of an electronic nose, in order to classify olive oil samples on the basis of their geographical origin. Counter-propagation maps were used as classification tools. 

Solvent extraction offers unique advantages among separation techniques. A system based on extraction into a polymer [poly(vinyl chloride)] as solvent was examined here because of possible advantages in speedy simplicity, sample size, solvent handlingy etc.f especially when coupled with flow injection and an amperometric detector. Solutes examined included salicylic acid and 8-hydroxy quinoline. The apparatus typically consisted of 0.8-mm i.d. X 170-cm coiled tubing that could be connected directly to the injection loop of a flow-injection amperometric detector system containing a nickel oxide electrode. 

Figure 3.23 Typical amperometric (readout during automated flow injection assays of ethanol solutions of increasing concentrations in 2 x 1CL5M steps at a carbon paste enzyme electrode detector. Curves a-h 2 x 10 SM - 1.6 x lCUM ethanol.

In a potentiostatic step experiment on an ultramicrodisc electrode, the current attains a limiting value in a time of the order r ID. In addition to this time scale becoming shorter with decreasing r, the mass transport rate of species to the electrode increases. As a consequence, one motivation for the development of devices using UMEs has been the resulting insensitivity of the limiting current to fluctuations of solution flow rate [62]. Hence UMEs have found widespread use as electrochemical detectors in fluid flow experiments, such as amperometric liquid chromatography (e.g., Ref. [63]) and flow injection analysis (e.g., Ref. [64]). Incidentally, this implies that the current should also be insensitive to vibration. 

The highest sample frequency achieved up to now has been obtained in a computer-controlled flow injection analysis (FIA) system (Olsson et al., 1986b) using an amperometric flow-through cell (Bertermann et al., 1981). A Pt electrode of 0.5 mm diameter (VEB Metra Radebeul, GDR) has been used as hydrogen peroxide detector. GOD was immobilized in polyurethane (thickness, 0.02 mm, enzyme loading, 50 U/cm2) and... 

Potentiometric electrodes of all types In flow-injection analysis (FIA) glass, ion-selective, amperometric electrodes, etc., can all theoretically be used in a detector cell to quantify some chemical substance. 

An important application of flow cells is their use as detectors in liquid chromatography (LC), capillary zone electrophoresis (CZE), and flow injection (FI) methods (46-50). Such cells may be coulometric ones, where all of the material flowing into the cell is electrolyzed, but more frequently they are amperometric or voltammetric cells, sometimes utilizing UMEs as described in Section 9.7. 

J. Matysik, E. Soczewinski, E. Zminkowska-Halliop, and M. Przegalinski, Determination of o-Diphenols by Flow Injection Analysis with an Amperometric Detector. Chem. Anal. (Warzaw), 26 (1981) 463. 

H. Ma and H. Yan, Study on Application of Flow Injection Analysis (FIA) with an Amperometric Detector—Determination of Silver Ion in Waste-waters by FIA [in Chinese]. Huanjing Huaxue, 1 (1982) 422. 

T. Yao, Flow Injection Analysis for Cholinesterase in Blood Serum by Use of a Choline-Sensitive Electrode as an Amperometric Detector. Anal. Chim. Acta, 153 (1983) 169. 

H. Huck, A. Schelter-Graf, and H. L. Schmidt, Measurement and Calculation of the Calibration Graphs for Flow Injection Analysis Using Enzyme Reactors with Immobilized Dehydrogenases and an Amperometric NADH Detector. Bioelectrochem. Bioenerg., 13 (1984) 199. 

H. Satake, Y. Kohri, and S. Ikeda, Flow Injection Analysis of Hydroqui-none, Pyrocatechol, Resorcinol and Pyrogallol with Amperometric Detector [in Japanese]. Nippon Kagaku Kaishi, 1 (1986) 43. 

D. Eadington and J. A. W. Dalziel, Reductive Determination of Metal Ions by Flow Injection Analysis Using Amperometric Amalgam Detectors. Anal. Proc., 23 (1986) 434. 

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