Determination of selected phenolic acids in beer extract by liquid chromatography with voltammetric-amperometric detection.

A voltammetric-amperometric detector for liquid chromatography based on a dual electrode electrochem-ical cell has been developed. This detector enables voltammograms to be obtained without the charging current problems inherent in single electrode voltammetric detectors. The detector is operated by scanning the potential of the upstream (voltammetric) electrode and detecting the electrolysis product at a constant potential (amperometric) electrode downstream. The reponse at the downstream amperometric electrode thus reflects the voltammetry occurring upstream but eliminates the charging current. The voltammetric-amperometric detector produces a three-dimensional data array of current response versus both time (chromatographic domain) and potential (electrochemical domain). This data array allows for several types of post-experimental data manipulation and display in order to enhance information retrieval. In this paper, these methods of display and manipulation of voltammetric-amperometric data are demonstrated for the determination of selected phenolic acids in an extract of a commercial beer sample. Electrochemical detection for liquid chromatography has become a widely used technique for the determination of trace amounts of organics because of the selectivity and low detection limits which can be achieved. Although most papers still describe the use of amperometric detectors with only a single working electrode, dual electrode amperometric detectors are becoming more popular.1.2 The use of dual electrode amperometric detectors provides advantages in selectivity, detection limits and qualitative information relative to single working electrode detectors. Voltammetric detectors with a single working electrode have also been reported.3-9 Voltam-metric detectors provide improved qualitative information from chromatographic effluents relative to detection at a single potential but typically have poorer detection limits because of large charging current backgrounds. We have previously described a voltammetric detector for flow injection analysis and liquid chromatography using a series configuration dual electrode thin-layer flow cell in which the potential at the upstream electrode is scanned while the potential of the downstream electrode is held constant .1&12 A similar approach has been described by Trubey and Niemanl3 using a coulostatic technique to achieve the potential sweep. The technique has been termed voltammetric-amperometic detection because the potential at the upstream electrode is scanned (voltammetric) while the downstream electrode is used to monitor the reaction at a constant potential (amperometric). In this way, the current response at the downstream electrode reflects the voltammetric behaviour of the analyte without the charging current associated with scanning the potential, In this paper, the voltammetric-amperometric determination of selected phenolic acids in beer is described, Experimental Apparatus The chromatographic …