Flow injection analysis of carbofuran in foods using air stable lipid film based acetylcholinesterase biosensor

This work describes a technique for the rapid, selective and sensitive electrochemical flow injection analysis of carbofuran in foods using air stable lipid films in which acetylcholinesterase was incorporated. These lipid films were supported on a methylacrylate polymer (i.e., methacrylic acid was the functional monomer for the polymerization, ethylene glycol dimethacrylate was used as the crosslinker and 2,2′-azobis-2-methylpropionitrile as an initiator). The substrate was injected into flowing streams of a carrier electrolyte solution. Hydronium ions produced by the enzymatic reaction at the lipid film surface caused dynamic alterations of the electrostatic fields and phase structure of membranes and as a result ion current transients were obtained; the magnitude of these signals was correlated to the substrate concentration, which could be determined at the micromolar level. The response times were ca. 10 s. These lipid membranes were used for the flow injection analysis of pesticides. The principle of the method is based on the degree of inhibition of the enzyme by the pesticide. Carbofuran was chosen as a typical pesticide. The novelty of the method is based on the fact that an “air segmented” flow injection technique can be used as compared to previous systems that are based on lipid film technology but are not stable in air. This allows determination of the pesticide using the degree of inhibition and reactivation of enzyme by injections of substrate. Carbofuran was determined at concentration levels of 10−7 to 10−9 M. The investigation of the effect of potent interferences included a wide range of compounds usually found in foods and also proteins and lipids. The technique was applied in 50 different real samples of fruits, vegetables and dairy products. The recovery ranged between ca. 96 and 106% which shows no interferences from the matrix effects.