COMPARISON OF PULSED AMPEROMETRIC DETECTION AND INTEGRATED VOLTAMMETRIC DETECTION FOR ORGANIC SULFUR-COMPOUNDS IN LIQUID-CHROMATOGRAPHY

A variety of potential-time waveforms are useful in pulsed electrochemical detection (FED) when applied for the amperometric detection of numerous polar organic compounds following their separation by liquid chromatography (LC). Here, we compare the waveforms for pulsed amperometric detection (PAD) and integrated voltammetric detection (IVD) applied for detection of organosulfur compounds at Au electrodes in acidic media. In PAD waveforms, electrode response is measured at a constant detection potential. In IVD waveforms, electrode current is integrated throughout a fast cyclic scan of the detection potential. As a consequence of this difference in detection strategy, the background signal for IVD is significantly smaller than for PAD in the detection of organosulfur compounds whose response mechanisms require the concomitant formation of surface oxides on Au electrodes. Furthermore, in comparison to PAD, IVD has a larger sensitivity and a diminished system peak from O-2 dissolved in the sample. Use of a preadsorption step increases detection sensitivity in both PAD and IVD. The limit of detection (S/N = 3) for cysteine in LC-IVD is ca. 6 nM for a 50-mu l injection (i.e., 300 fmol) using a detection waveform that includes a 1000-ms preadsorption period.