The pesticide, methyl isothiocyanate call be determined based on its inhibitory effects on an amperometric horseradish peroxidase-modified electrode, in non-aqueous media. The apparent inhibition constant, K-i', was evaluated using steady-state binding kinetics and was used as a measure of sensor efficiency. K-i' was found to be 0.27 mmol/l, 0.18 mmol/l and 0.37 mmol/l in acetonitrile, methanol and 2-butanol, respectively. A correlation was observed between K-i' values and some physical properties of the solvents such as polarity, kinematic viscosity and dielectric constant. A possible solvent-induced deviation of the biosensor from Michaelis-Menten kinetics was evaluated based on a comparism of Hill coefficients. The least deviation was observed in 2-butanol (Hill coefficient = 1.04), whereas the greatest deviation was in methanol (Hill coefficient = 3.19) which exhibited the highest sensor efficiency.
