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CYCLODEXTRIN HOST-GUEST RECOGNITION APPROACH FOR SIMULTANEOUS QUANTIFICATION AND VOLTAMMETRIC STUDIES OF LEVODOPA AND CARBIDOPA IN PHARMACEUTICAL PRODUCTS AND A SENSITIVE METHOD BASED ON SCANNER SPECTROSCOPY FOR DETERMINATION OF NITRITE IN FOODSTUFFS

Name: CYCLODEXTRIN HOST-GUEST RECOGNITION APPROACH FOR SIMULTANEOUS QUANTIFICATION AND VOLTAMMETRIC STUDIES OF LEVODOPA AND CARBIDOPA IN PHARMACEUTICAL PRODUCTS AND A SENSITIVE METHOD BASED ON SCANNER SPECTROSCOPY FOR DETERMINATION OF NITRITE IN FOODSTUFFS
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M.Sc.Thesis in Analytical Chemistry

CYCLODEXTRIN HOST-GUEST RECOGNITION APPROACH FOR SIMULTANEOUS QUANTIFICATION AND VOLTAMMETRIC STUDIES OF LEVODOPA AND CARBIDOPA IN PHARMACEUTICAL PRODUCTS

AND

A SENSITIVE METHOD BASED ON SCANNER SPECTROSCOPY FOR DETERMINATION OF NITRITE IN FOODSTUFFS

An electrochemical sensor for simultaneous quantification of Levodopa (L-dopa) and Carbidopa (C-dopa) using a β-cyclodextrin/poly(N-acetylaniline) (β-CD/PNAANI) modified carbon paste electrode has been developed. The overlapping anodic peaks of L-dopa and C-dopa at 810 mV on bare carbon paste electrode resolved in two well-defined voltammetric peaks at 450 and 880 mV vs Ag/AgCl, respectively, Under optimized conditions, linear calibration curves were obtained in the ranges of 0.5 – 117 µM and 1.6 – 210 µM with detection limits down to 0.2 and 0.8 µM for L-dopa and C-dopa, respectively.

A simple method for determination of nitrite is described based on the Griess diazo-coupling reaction of sulfanilic acid and α-naphtylamine yielding an azo dye. In the current study, the cells were built by creating holes in the Plexiglas^® sheet using a laser beam and serve as miniaturized reaction chambers containing the sample solution. These were scanned with a conventional flatbed-scanner, then the color of each cell was analyzed with photoshop software. The proposed sensor displays a linear response in concentration range of 0.069-3.79 μg mL^-1 of nitrite and has detection limit of 0.01 μg mL^-1.

دسته: زبان خارجه, زبان خارجه برچسب: A SENSITIVE METHOD BASED ON SCANNER SPECTROSCOPY FOR DETERMINATION OF NITRITE IN FOODSTUFFS, CYCLODEXTRIN HOST-GUEST RECOGNITION APPROACH FOR SIMULTANEOUS QUANTIFICATION AND VOLTAMMETRIC STUDIES OF LEVODOPA AND CARBIDOPA IN PHARMACEUTICAL PRODUCTS

توضیحات

CONTENTS………………………………………………………….PAGE

CHAPTER ONE

EXPERIMENTAL…………………………………………………….46

3.1. Cyclodextrin host-guest recognition approach for simultaneous quantification and voltammetric Studies of levodopa and carbidopa in Pharmaceutical products. 46

VI

3.1.4. Procedure. 49

3.2. Simple and cost effective method for determination of nitrite based on development of scanner spectrophotometry.. 50

VIII

LIST OF FIGURES

FIGURE …………………….……………………………………………PAGE

Fig.1.1 Chemical structures of α- (left), β- (middle) and γ-cyclodextrin (right)……………………………………………………………………………3

Fig.1.2.Three dimensional structure of cyclodextrin…………………………..4

Fig.1.3. X-ray crystal structures of a cyclodextrin containing 14(a) and 26(b) sugar units………………………………………………………………………6

Fig.1.4. Complexation of cyclodextrin with ferrocene dendrimers as a multisite guest……………………………………………………………………………9

Fig.1.5. Redox control of the β-CD complexation of viologens………………11

Fig.1.6. Formation of a dendrimer-cyclodextrin assembly (top) and the electrochemically controlled adsorption at the β-cyclodextrin host surface (below)………………………………………………………………………..13

Fig.1.7. Mechanism for the β-CD Incorporation into the PNAANI Film……………………………………………………………………………19

Fig.3.1. Consecutive cyclic voltammograms of the growth of PNAANI film at CPE in a solution containing 0.1 M N-acetylaniline and 1 M HClO₄. Scan rate: 100mVs^-1……………………………………………………………………………………………..48

Fig.3.2. ¹H NMR spectra of β-CD (A) and β-CD/PNAANI film (B) in DMSO-d₆………………………………………………………………………………49

IX

Fig.3.3. Cell array on the sheet………………………………………………..50

Fig. 4.1. Schematic representation of L-dopa(a) and C-dopa(b) inclusion onto CD cavity…………………………………………………………………………………56

Fig.4.2. Cyclic voltammograms of (A) 1.0 mM L-dopa, (B) 1.0 mM C-dopa and (C) 1.0 mM L-dopa and C-dopa in 0.1 M PBS obtained using β-CD/PNAANI/CPE (a), bare carbon paste electrode (b), blank supporting electrolyte (c) and PNAANI/CPE (d) at 25 °C. Scan rate: 100mVs^-1…………………………………………………………………………………………………………..58

Fig.4.3. Left:Cyclic voltammograms of carbidopa(0.5 mM) on β-CD/PNAANI/CPE in 0.1 M PBS at pH 7.0. right: plot of anodic peak current versus the square root of scan rate for carbidopa(top) and levodopa(below). Scan rates increasing from 5 to 500mV/s (a to i)…………………………………………………………………………………………………………60

Fig.4.4. CVs of L-dopa in 0.1 M phosphate buffer pH 7.0 recorded following its preconcentration onto a β-CD/PNAANI/CPE by adsorptive accumulation in a solution of 0.5mM L-dopa in sample solution (a) and after transferring the electrode to the supporting electrolyte in the absence of L-dopa (b).scan rate: 100mVs^-1……………………………………………………………………………………………..61

Fig.4.5. Plot of peak potential versus pH of the solution for 0.5 mM of levodopa(right) and 0.5 mM of carbidopa(left) in 0.1 M phosphate buffer pH 7.0.scan rate 100mVs^-1………………………………………………………..62

Fig.4.6. The proposed L-dopa oxidation mechanism at β-CD/PNAANI /CPE…………………………………………………………………………..63

X

Fig.4.7. Differential-pulse voltammograms (DPV) obtained at β-CD/PNAANI/CPE in: A) 100 μM L-dopa before (dotted line) and after (solid line) addition of 100 μM C-dopa; B) 96 µM L-dopa in different concentrations of C-dopa (24, 49, 72.8 and 96 µM, from bottom to top) in 0.1 M PBS at pH 7.0……………………………………………………………………………………………………….64

Fig.4.8. Differential-pulse voltammograms (DPV) obtained for 96 µM C-dopa before (a) and after (b) addition of 96µM L-dopa at β-CD/PNAANI /CPE in 0.1 M PBS at pH 7………………………………………………………………………………..65

Fig.4.9. C/Γ νs. C plots of anodic peak current for L-dopa and C-dopa on β-CD/PNAANI/CPE. scan rate 100 mVs^-1…………………………………………………..67

Fig.4.10. DPVs for the L-dopa and C-dopa at β-CD/PNAANI/CPE in 0.1M phosphate buffer at pH 7.0 and different concentrations of analytes: 0.7-117 µM for L-dopa and 1.65-210 µM for C-dopa. Accumulation time 30 s; pulse amplitude 0.05 V; voltage step 0.006 V; sweep rate 0.015 V s^-1. inset is the calibration curve of L-dopa and C-dopa…………………………………………………………………………………………………….69

Fig.4.11. Effect of sulfanilic acid concentration on color intensity in 10 µM of nitrite solution and 1M of H₂SO₄……………………………………………..74

Fig.4.12. Effect of α-naphtylamine concentration on color intensity at optimum conditions……………………………………………………………………76

Fig.4.13. Effect of sulfuric acid concentration on color intensity at optimum conditions…………………………………………………………………………………………….78

Fig.4.14. Effect of time on color intensity at optimum conditions…………………………………………………………………………………………….83

XI

LIST OF TABLES

TABLE ……………………………………………………………….….PAGE

Table 1.1. Diameters of α, β and γ CDs………………………………………..5

Table 2.1. Comparison of spectrophotometric methods for the determination of nitrite………………………………………………………………………….44

Table 4.1. Maximum surface coverages (Γ_max) and the apparent association constants (K_ass) for the complexation of L-dopa and C-dopa with β-CD at an ambient temperature…………………………………………………………..68