New enzyme sensors for morphine and codeine based on morphine dehydrogenase and laccase

Two new enzymatic methods have been developed to quantify morphine and codeine simultaneously in a flow injection system (FIA). The first enzyme sensor for morphine or codeine is based on immobilizing morphine dehydrogenase (MDH) and salicylate hydroxylase (SHL) on top of a Clark-type oxygen electrode. Morphine or codeine oxidation by MDH leads to a consumption of oxygen by SHL via the production of NADPH. This decreases the oxygen current of the Clark electrode. Concentrations of codeine and morphine are detected between 2 and 1000 mu M and between 5 and 1000 mu M, respectively. The second enzyme sensor for morphine is based on laccase (LACC) and PQQ-dependent glucose dehydrogenase (GDH) immobilized at a Clark oxygen electrode. Morphine is oxidized by laccase under consumption of oxygen and regenerated by glucose dehydrogenase. Since laccase cannot oxidize codeine, this sensor is selective for morphine. Morphine is detected between 32 nM and 100 mu M. Both sensors can be operated simultaneously in one flow system (FIA) giving two signals without the requirement for a separation step. This rapid and technically simple method allows discrimination between morphine and codeine in less than 1 min after injection. The sampling rate for quantitative measurements is 20 h(-1). The method has been applied to the quantitative analysis of codeine or morphine in drugs.