| A thin-layer type of amperometric detector is used to detect anionic species in both flow-injection and anion chromatography systems. The detector is shown to respond to anionic species on the basis of conductivity changes during the passage of sample plugs in the detector cell, no matter whether the anionic species are electrochemically-active or inactive.; The working electrode of this amperometric cell is constructed from a conducting, copper-based compound which was the insoluble fraction from the chemical polymerization of 3-methyl-2,5-dibromothiophene using copper chloride as catalyst. This material exhibits a dramatic increase in conductivity on "doping" with water, and a remarkable electrochemical stability in aqueous media. This material was previously considered as a copper-containing poly(3-methyl-thiophene). After careful characterization by elemental analysis, FT-IR, ESCA, CV and solubility tests, it is found that this material is mainly an inorganic compound containing Cu(I/II) cations and cyano- and hydroxy-groups.; This amperometric detector is used for the measurement of inorganic anions; F{dollar}sp-{dollar}, Cl{dollar}sp-{dollar}, Br{dollar}sp-{dollar}, NO{dollar}sbsp{lcub}2{rcub}{lcub}-{rcub}{dollar}, and NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar} in both single-column and eluant-suppressed anion chromatography. The chromatograms obtained with this detector and with a commercial conductivity detector are virtually indistinguishable under the same chromatographic conditions. The results show that the limits of detection for both detectors are comparable. The working electrode used exhibits greater stability and sensitivity than other electrode materials, such as platinum, stainless steel and cuprous cyanide, when used in the same detector units.; Although the actual mechanism of the response to anions by the copper-based compound electrode is not proved, a possible mechanism is suggested that electrode oxidation current observed occurs when a positive potential (vs. Ag/AgCl) is applied to the electrode, and the magnitude of anodic current depends on the conductivity of the analyte plug passing through the detector cell. |
