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 media using a horseradish peroxidase modified platinum electrode is reported. The performance of the electrode is based on the inhibitory effect 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, ethylenethiourea, and mercaptoethanol, respectively. The current as peroxide concentration approaches infinity in the absence of any inhibitor (I(max), and the apparent inhibition constant (K'(i)) for each inhibitor were evaluated. I(max)/K'(i)), i.e. the percentage inhibition of sensor response per millimolar of each inhibitor, was calculated and used as a measure of the performance of the sensor in the determination of the organic sulphides. From these values the sensitivity trend of the biosensor for the organic sulphides is ethylenethiourea > thiourea > mercaptoethanol. The kinetic effects of other operational parameters such as mediator concentration, water content of the solvent and working potential were also evaluated to assess analytical performance.