Amperometric flow injection analysis of organic thiols and proteins

The amperometric determination of thiols by injection into a mercury carrier stream is shown to be a sensitive method when using a tungsten wire as the working electrode in a three-electrode flow cell. Hg2+ gives sharp peaks when injected into phosphate buffer at pH 3.1 at an operating voltage of -0.24 V (against a Ag/AgCl reference electrode). Hg2+ was determined in the range 0.43 to 25.0 mu M with linear response. Injection of cysteine into the mercury carrier causes a decrease in the cathodic current, and sharp flow injection peaks are observed with a peak width of approximately 60s. Optimization of various parameters was performed, including buffer effects, mercury concentration, injection volume, and the effects of various cations and anions on the response were determined. Linear calibrations in the range 0.25 mu M to 100 mu M for cysteine and 1.3 to 1000 ng for the other thiols glutathione, thiourea, albumin, and DNA were found. The responses to cysteine and thiourea were most sensitive, and interference from silver and iodate was observed at concentrations in excess of the thiols. The method may be used as a rapid means of detecting thiols in various samples and as an HPLC detection method.