Electrochemical determination of some substances important for food safety

The aim of this thesis was the development of a sensor based on modified electrodes for the determination of some substances important for food safety such as sodium nitrite (E250), sunset yellow (E110), bisphenol A and ascorbic acid (E300), and electrochemical determination of these substances with the developed sensor. For sensors, the use of pencil graphite (PG) electrodes modified with poly (methylene blue) (PMB), gold nanoparticle (GNP), chemically treated multi-wall carbon nanotube (MWCNT-COOH), copper(II) phthalocyanine (CuPc) and poly(ethylenedioxythiophene) (PEDOT) were investigated. Electrode preparation and measurement conditions were optimized in order to improve the sensitivity performance of the prepared modified electrodes to analytes. The thesis consists of 4 stages. In the first stage, PG electrodes modified with poly(methylene blue) and gold nanoparticles were prepared for determination of nitrite (GNP/PMB/KUG). The GNP/PMB/KUG showed good selectivity and sensitivity for nitrite. The linear range of the prepared sensor was found to be 5.0-5000 μM under optimized conditions. Its limit of detection (LOD) was 0.3 μM. In the second stage, KUG electrodes modified with poly(L-cysteine) (PLS/KUG) were prepared for detection of sunset yellow. The prepared electrodes showed good selectivity and sensitivity for sunset yellow. The linear range of the prepared sensor under optimized conditions was found to be 1.0-1000 μM. Its limit of detection (LOD) was 0.125 μM. In the third stage, the activity of KUG electrodes modified with copper(II) phthalocyanine and chemically treated multi-walled carbon nanotube (CuPc/MWCNT-COOH/KUG), synthesized and characterized for the first time in this thesis study, in the detection of bisphenol A was investigated. The linear range of the prepared sensor under optimized conditions was found to be 0.075-27.5 μM. Its limit of detection (LOD) was 0.0189 μM. In the final stage, PG electrodes modified with chemically treated multi-walled carbon nanotube and over-oxidized poly(ethylenedioxythiophene) (MWCNT-COOH/AY-PEDOT/KUG) were prepared for ascorbic acid detection. The resulting electrodes showed good selectivity and sensitivity for ascorbic acid. The linear range of the prepared sensor under optimized conditions was found to be 5.0-750 μM. Its limit of detection (LOD) was 2.7 μM. The characterization and morphology studies of the prepared modified electrodes were carried out by cyclic voltammetry, electrochemical impedance spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. In addition, the performances of the modified electrodes were examined in the presence of interfering species. Finally, the effectiveness of the modified electrodes was tested on real samples of food and beverages. The obtained results show that the modified electrodes have the superior features such as low cost, easy preparation, disposability, short response time, high sensitivity and selectivity, which are essential characteristics that an ideal sensor should have. We can conclude that the modified electrodes prepared in this thesis can be used as alternative sensors in the detection of sodium nitrite, sunset yellow, bisphenol A, and ascorbic acid.