Evaluation of a highly sensitive amperometric biosensor with low cholinesterase charge immobilized on a chemically modified carbon paste electrode for trace determination of carbamates in fruit, vegetable and water samples

A highly sensitive amperometric biosensor for determination of carbamate pe sticides directly in water, fruit and vegetable samples has been evaluated, electrochemically characterized and optimized. The biosensor strip was fab ricated in screen printed technique on a ceramic support using silver-based paste for reference electrode, and platinum-based paste for working and au xiliary electrodes. The working electrode was modified by a layer of carbon paste mixed with cobalt(II) phthalocyanine and acetylcellulose. Cholineste rase (ChE) enzymes with low enzymatic charge were immobilized on this layer . The operational simplicity of the biosensor consists in that a small drop (similar to 50 mu l) of substrate or sample is deposited on a horizontally positioned biosensor strip representing the microelectrochemical cell. The working potential of the biosensor was 370 mV versus Ag/AgI on a ship refe rence electrode preventing the interference of electroactive species which are oxidable at more positive potentials. The biosensor was applied to inve stigate the degradation of two reference ChE inhibitors in freeze dried wat er under different storage conditions and for direct determination of some N-methylcarbamates (NMCs) in fruit and vegetable samples at ppb concentrati on levels without any sample pretreatment. A comparison of the obtained res ults for the total carbamate concentration was done against those obtained using HPLC measurements. (C) 1999 Elsevier Science B.V. All rights reserved .