DETERMINATION OF KINETIC-PARAMETERS FR THE INHIBITORY EFFECTS OF ORGANIC SULFIDES ON AN AMPEROMETRIC PEROXIDE BIOSENSOR IN NONAQUEOUS MEDIA

The amperometric detection of some organic sulphides in non-aqueous me dia using a horseradish peroxidase modified platinum electrode is repo rted. The performance of the electrode is based on the inhibitory effe ct of sulphides on the activity of peroxidase. The electrode responds rapdily to micromolar concentrations of the sulphides with linearities extending up to 0.4, 0.25 and 0.8 mmol/dm3 for thiourea, ethylenethio urea, and mercaptoethanol, respectively. The current as peroxide conce ntration approaches infinity in the absence of any inhibitor (I(max), and the apparent inhibition constant (K'(i)) for each inhibitor were e valuated. I(max)/K'(i)), i.e. the percentage inhibition of sensor resp onse per millimolar of each inhibitor, was calculated and used as a me asure of the performance of the sensor in the determination of the org anic sulphides. From these values the sensitivity trend of the biosens or for the organic sulphides is ethylenethiourea > thiourea > mercapto ethanol. The kinetic effects of other operational parameters such as m ediator concentration, water content of the solvent and working potent ial were also evaluated to assess analytical performance.