Amperometric selective biosensing of dimethyl- and diethyldithiocarbamates based on inhibition processes in a medium of reversed micelles

An amperometric tyrosinase electrode has been used for biosensing of dimethyl- and diethyldithiocarbamates based on the inhibition effects of these substances on the catalytic activity of the enzyme. A working medium consisting of reversed micelles, and phenol as the substrate has been used. The tyrosinase electrode was constructed by direct adsorption of the enzyme on the surface of a graphite-disk electrode. Reversible inhibition processes are shown to be involved for ziram, diram and zinc diethyldithiocarbamate. Following a simple regeneration of the enzyme electrode, an acceptable reproducibility for the measurements of the inhibition response was obtained. Experimental variables, such as temperature, phenol concentration and the presence of chloroform, affecting the inhibition processes, were optimized. The type of enzyme inactivation for each inhibitor tested was studied, and the inhibition constants were calculated. Detection limits of 0.074, 1.3 and 1.7 μmol l−1 were achieved for ziram, diram and zinc diethyldithiocarbamate, respectively. Other carbamates belonging to families different from dimethyl- and diethyldithiocarbamates showed no amperometric response at the tyrosinase electrode, except for pyrimidine-derivative carbamates. The developed analytical methodology was applied to determine ziram in spiked apple samples.