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Title of Thesis

Formulation And Stability Of Ascorbic Acid In Liquid And Semisolid Preparations

Author(s)

Muhammad Ali Sheraz

Institute/University/Department Details
Department of Pharmaceutics, Faculty of Pharmaceutical Sciences / Baqai Medical University, Karachi
Session
2009
Subject
Pharmaceutics
Number of Pages
241
Keywords (Extracted from title, table of contents and abstract of thesis)
Photodegradation, Vitamins, Redox, Potentials, Stability, Formulation, Semisolid, Preparations, Liquid, Acid, Ascorbic, Tartaric

Abstract
The present investigation is based on a study of the photodegradation of ascorbic acid (vitamin C) in organic solvents and in oil-in-water cream preparations containing a combination of emulsifying agents and humectants. It also involves the study of the effect of other vitamins (riboflavin, nicotinamide and alpha-tocopherol) and certain compounds acting as stabilizing agents (citric acid, tartaric acid and boric acid) on the rate of photodegradation of ascorbic acid in cream preparations. The photodegradation of ascorbic acid in organic solvents and cream preparations (pH 4.0–7.0) leads to the formation of dehydroascorbic acid which is also biologically active. The kinetics of photodegradation of ascorbic acid alone and in combination with other vitamins in creams has been studied using a UV spectrophotometric method and the official iodimetric method, respectively. These methods were validated in the presence and absence of other vitamins / stabilizing agents under the experimental conditions employed. The recoveries of ascorbic acid in creams are in the range of 90–96% and the reproducibility of the analytical methods is within 5%.
The apparent first-order rate constants (kobs) for the photodegradation of ascorbic acid in aqueous / organic solvents (0.29–0.40 10–3 min–1) and in creams (0.44–1.42 10–3 min–1) have been determined. A linear relationship has been observed between kobs and solvent dielectric constant / reciprocal of solvent viscosity indicating the dependence of the rate of photodegradation on solvent characteristics.
In the creams the photodegradation of ascorbic acid appears to be affected by the concentration of other vitamins, pH of the medium, carbon chain length of the emulsifying agents (myristic acid, palmitic acid and stearic acid), viscosity of the humectant (ethylene glycol, propylene glycol and glycerin) and redox potentials of ascorbic acid. The study indicates that the relative polar character of the emulsifying agent and the ionized state and redox potential of ascorbic acid at a particular pH are important factors in the photodegradation of ascorbic acid in creams.
The second-order rate constants (k ) (3.20 10–2 – 1.89 M–1 min–1) for the photochemical interaction of ascorbic acid and the individual vitamins (riboflavin, nicotinamide, alpha-tocopherol) along with the values of k0 obtained from the intercepts of the plots of kobs versus vitamin concentration are also reported. The values of k0 indicate that riboflavin and nicotinamide act as photosensitizing agents, and alphatocopherol acts as a stabilizing agent in the photodegradation of ascorbic acid in the creams. The kobs verses pH profiles for the photodegradation of ascorbic acid in creams represents sigmoid type curves indicating the oxidation of the ionized form (AH–) of ascorbic acid (pKa1 4.1), with pH. The AH– species appears to be more susceptible to photooxidation than the non-ionized form of ascorbic acid. The effect of stabilizing agents on the photodegradation of ascorbic acid has been found to be in the order of citric acid > tartaric acid > boric acid. The low activity of boric acid may be to some extent due to its interaction with the emulsifying agents and humectants. The polarity of the emulsifying acids also plays a part in the rate of degradation of ascorbic acid. Reaction schemes for the photodegradation of ascorbic acid and its photochemical interaction with riboflavin, nicotinamide and alpha-tocopherol have been presented.

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1,544 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 CONTENTS
 

 

ix
43 KB
2 1 INTRODUCTION

1.1 Historical Background
1.2 Physicochemical Characteristics Of Ascorbic Acid
1.3 Chemistry Of Ascorbic Acid
1.4 Biochemical Functions
1.5 Antioxidant Activity
1.6 Photostability Of Drugs
1.7 Kinetic Treatments Of Photochemical Reactions
1.8 Literature On Ascorbic Acid

1
96 KB
3 2 PHOTODEGRADATION REACTIONS AND ASSAY OF ASCORBIC ACID

2.1 Photodegradation Reactions
2.2 Assay Of Ascorbic Acid

17
93 KB
4 3 FORMULATION AND STABILITY OF CREAM PREPARATIONS

3.1 Formulation Of Cream Preparations
3.2 Formulation Of Ascorbic Acid Creams
3.3 Stability Of Creams

31
97 KB
5 4 MATERIALS AND METHODS

4.1 Materials
4.2 Methods
 

51
103 KB
6 5 PHOTODEGRADATION OF ASCORBIC ACID IN ORGANIC SOLVENTS AND CREAM FORMULATIONS

5.1 Introduction
5.2 Photoproducts Of Ascorbic Acid
5.3 Spectral Characteristics Of Photolysed Solutions
5.4 Assay Of Ascorbic Acid In Creams And Solutions
5.5 Effect Of Solvent
5.6 Effect Of Concentration
5.7 Effect Of Carbon Chain Length Of Emulsifying Agent
5.8 Effect Of Viscosity
5.9 Effect Of Ph
5.10 Effect Of Redox Potential
5.11 Primary Photochemical Reactions In The Oxidation Of Ascorbic Acid
5.12 Degradation Of Ascorbic Acid In The Dark

68
311 KB
7 6 PHOTOCHEMICAL INTERACTION OF ASCORBIC ACID WITH RIBOFLAVIN, NICOTINAMIDE AND ALPHA-TOCOPHEROL IN CREAM FORMULATIONS

6.1 Introduction
6.2 Absorption Characteristics Of Photolysed Creams
6.3 Photoproducts Of Ascorbic Acid And Other Vitamins
6.4 Assay Method 116
6.5 Kinetics Of Photodegradation Of Ascorbic Acid
6.6 Interaction Of Riboflavin With Ascorbic Acid
6.7 Interaction Of Nicotinamide With Ascorbic Acid
6.8 Interaction Of Lpha-tocopherol With Ascorbic Acid
6.9 Effect Of Carbon Chain Length Of Emulsifying Agent
6.10 Effect Of Viscosity Of Creams
6.11 Degradation Of Ascorbic Acid In The Presence Of Other Vitamins In The Dark

109
251 KB
8 7 STABILIZATION OF ASCORBIC ACID WITH CITRIC ACID, TARTARIC ACID AND BORIC ACID IN CREAM FORMULATIONS

7.1 INtroduction
7.2 Cream Formulations
7.3 Products Of Ascorbic Acid Photodegradation
7.4 Spectral Changes In Photodegraded Creams
7.5 Assay Of Ascorbic Acid In Creams
7.6 Kinetics Of Photodegradation
7.7 Effect Of Stabilizing Agents
7.8 Degradation Of Ascorbic Acid In Presence Of Stabilizing Agents In The Dark
7.9 Effect Of Additives On Transmission Of Ascorbic Acid

141
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9 8 REFERENCES 185
202 KB