Preparation of polymer membrane based single electrod biosensor system and application for determination of nitrite and nitrate

Nitrates and nitrites are undesired food additives because of their adverse effects on human health. Toxicity of these food additives arises from the formation of carcinogenic nitrosamines between nitrite and secondary amines present in human body. Furthermore, consumption of nitrates and nitrites in foods may cause methaemoglobinaemia. Nitrites and nitrates are added to meat products to inhibit the growth of Clostridium botulinum and to enhance unique flavor of cured meat products. However, food laws strictly restrict the amount of nitrite and nitrate added to foods. Nitrite and nitrate concentrations in water supplies are good indicators for water quality. Increase in the nitrate and nitrite concentrations of foods causes a significant concern for public health. Therefore, nitrate and nitrite contents of foods must be monitored periodically. In this thesis, which prepared by immobilization of nitrate reductase enzyme with polyurethane polymers they contains different carbohydrates have been developed for determination nitrite and nitrate with a single electrode. Nitrite was monitored at +0,87 V Differential Pulse Voltammetry (DPV) technique with these biosensors prepared on platin electrode surface. In line with the studies on optimization of enzyme based biosensors for nitrate determination the response time 2 minutes, enzyme amount 0,5 U, coenzyme amount (NADPH) 0,25 mM and optimum temperature were determined as 25 oC. Additionally, the best biosensor responses were obtained with 100 mM, pH 7,5 phosfate buffer. The largest linear range for nitrite was attained with the biosensor prepared with PU-Maltoz-%1 polymer at 0,25 mM - 125 mM concentration interval. The largest linear range for nitrate was found as 1 mM - 10 mM in five biosensors. After the optimization studies, the characterization studies of the biosensors were done. For this purpose, repeatability, intereference effect, operational stability and storage stability were examined. In addition, on the optimized conditions with these biosensors, amounts of nitrit and nitrate were determined on salami, sausage, and waste water samples.