| Description |
The sulfhydryl group of low molecular thiols including cysteine is reactive and is often found conjugated to other molecules such as nitric oxide and/or metal ions via its sulfhydryl moiety. Therefore, it is not surprising that thiols play key role in many protective mechanisms against adverse effects of metal ions. On the other, good affinity of their -SH moiety can be used as a base for heavy metal ion sensor in environmental analysis. Electrochemical measurements were performed Trace Analyzer and autosampler, using a standard cell with three electrodes and cooled sample holder (4 degrees C). For automated samples handling prior to their electrochemical and photometrical analysis, an automated pipetting station with computer controlling was used. Ellman reaction for -SH group detection was measured using Chemical Analyser. In this study, we primarily aimed our attention on studying of basic electrochemical behaviour of cadmium(II) ions and low molecular mass thiol cysteine. Measured concentrations of cysteine were 0, 0.5, 1, 2.5, 5, 10, 25, 50, 75, 100, 150, 200, 250, 500, 750 and 1000 mu M, and cadmium(II) ions 0, 0.5, 1, 2.5, 5, 10, 25, 50, 75, 100, 150, 200, 250, 500, 750 and 1000 nM. Well developed peaks of cadmium(II) ions at -0.6 V and -SH moiety at -0.2 V and at coloured complex 412 nm were detected. After that we characterized the obtained differential pulse voltammograms, we followed with the studying of their mutual interactions. Each from the above mentioned thiols concentrations were mixed with 0.5, 1, 2.5, 5, 10, 25, 50, 75, 100, 150, 200, 250, 500, 750 or 1000 nM cadmium(II) ions and incubated. Based on the affinity of -SH moiety to metal ion, cadmium-thionein complexes were formed. Samples were taken in the following time intervals: 0, 5 and 15 h and measured using differential pulse voltammetry. The changes in the signals as rapid decreasing of cadmium(II) ion peak and free thiol moiety, and occurring of Cd-S complex peak were described and mathematically and statistically evaluated. Based on the statistics, we were able to estimate mathematical calibration model, detection limits and quantification limits for determination of cadmium(II) using sensors based on cysteine.
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