Development of New Electrochemical Methods for Analysis of Tryptophan and its Derivatives in Biological Environments (Metabolites) based on Nanosized Molecularly Imprinted Polymers and Modified Carbon based Electrodes

Amjadi, Somayeh (2017) Development of New Electrochemical Methods for Analysis of Tryptophan and its Derivatives in Biological Environments (Metabolites) based on Nanosized Molecularly Imprinted Polymers and Modified Carbon based Electrodes. Doctoral thesis, University of Mohaghegh Ardabili.

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Text (توسعه روش‌های جدید آنالیز الکتروشیمیایی تریپتوفان و مواد مشتق از آن در محیط بیولوژیکی (متابولیت¬ها) بر اساس تکنولوژی قالب¬زنی مولکولی در ابعاد نانو متری و الکترود¬های کربنی اصلاح شده) Somayeh Amjadi.pdf Download (1MB) | Preview

Abstract

In this thesis, the use of modified carbon electrodes with nano-materials such as molecular imprinted polymer, carbon nanotubes, graphene and some metal oxide electrocatalysts for the analysis of tryptophan and certain of its derivatives have been studied. This project consists of three parts; In the first part, a new sensor using a glassy carbon electrode modified with nano composite based on multi-walled carbon nanotubes and molecularly imprinted polymer was presented. Since tryptophan is insoluble in non-polar organic solvents (acetonitrile and chloroform), synthesis of the molecularly imprinted polymer for tryptophan is difficult and from challenging discussions. In this project, after various studies and theoretical studies (DFT Computations), the appropriate functional monomer was designed and synthesized that interaction of this monomer with tryptophan in polar solvents such as methanol is strong enough. Prepared monomer was used for synthesis of molecularly imprinted polymer. The proposed sensor in comparison with the reported methods, have a lower detection limit, broader linear range, higher sensitivity and better selectivity. In the second part, the new electrochemical methods for the analysis of nicotinic acid was introduced. To the best of our knowledge, the determination of this compound using a carbon paste electrode (CPE) has not been exploited. But in this project, a significant peak was observed for the nicotinic acid on carbon paste electrode by examining various parameters such as the pH of the electrolyte solution, electrode composition and selection of appropriate voltammetry technique. The proposed sensor was successfully used for the analysis of nicotinic acid in pharmaceutical and biological samples. In the next step, the sensor with better analysis characteristics was provided by modifying of carbon paste electrode. For this purpose, after various surveys, nicotinic acid-imprinted polymer was synthesized and its composites with graphene was used to modify carbon paste electrode. The modified electrode was unable to direct analysis of nicotinic acid. For solve the problem, the indirect method (using copper ion as electroactive probe) was used.With this method, the low detection limit and very high sensitivity was obtained. In the third part, the new electrochemical methods for the analysis of melatonin was introduced. According to reports, the oxidation peak of melatonin and tryptophan overlap and since these two materials coexist in most of the real samples, separation of oxidation peak of them is important. Based on the mechanism of oxidation of melatonin and using from appropriate voltammetry methods (square wave voltammetry by applying the appropriate pre-potential) oxidation peak melatonin not only completely isolated from the peak of tryptophan oxidation, also its intensity was multiplied. The proposed sensor was used to determination of melatonin in pharmaceutical and food samples. Finally, the sensor with suitable analytical properties for simultaneous measurement of melatonin, tryptophan and ureic acid using carbon paste electrode modified with MnO2/TiO2 nanocomposite was presented.

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