Potentiometric butyrylcholine sensor for organophosphate pesticides.

A highly sensitive potentiometric butyrylcholine (BuCh) sensor based on plasticized poly(vinyl chloride) membrane was fabricated using tetrakis (3,5-bis[2-methoxy-hexafluoro-methyl] phenyl) borate (HFPB) as a cation exchanger. The sensor showed a Nernstian response from 10(-1) M to 10(-6) M for BuCh. The detection limit of the sensor was 1.8 x 10(-7) M. The potential stability, lifetime and detection limit of the BuCh-sensor were improved in comparison with corresponding parameters of BuCh-sensors using prepared other cation exchangers. This improvement was proved to be due to higher hydrophobicity of the cation exchanger, HFPB. Enzyme activity of butyrylcholinesterase (BuChE) was determined by the BuCh-sensor fabricated. Since the selectivity coefficient of the BuCh-sensor for BuCh against a product of the enzyme reaction, choline, was as low as 6.3 x 10(-3), the sensor was not affected by interference from choline even when the enzyme reaction proceeded up to about 80%. Michaelis parameters for the BuChE reaction were obtained by the sensor. Determinations of organophosphate pesticides, 2,2-dichlorovinyldimethylphosphate and o-(4-bromo-2-chlorophenyl)o-ethyl S-propylphosphothiolate) were conducted by measuring inhibition of enzyme activity. The enzyme reaction rate was related to the concentration of pesticides. Pesticides were successfully determined between micromole and sub-nanomole levels by the BuCh-sensor.