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Vitamins are essential micronutrients required for normal growth and biochemical functions. Riboflavin (Vitamin B2) is a water-soluble vitamin present in dairy products, vegetables, wheat, egg yolk, and meat. A number of techniques have been used for the analysis of riboflavin alone and in mixtures including UV and visible spectrometry, mass spectrometry, fluorimetry, chromatography and electrochemical methods. This article presents a mini review of the analytical methods that are used for the determination of riboflavin (vitamin B2) in pharmaceutical products, food materials, and biological samples. These methods are based on spectral and electrochemical characteristics of riboflavin. [ABSTRACT FROM AUTHOR]

The kinetics of photolysis of ascorbic acid in aqueous solution on UV irradiation has been studied in the pH range 1-11 and the apparent first--order rate constants for the degradation reactions have been determined. The k-pH profile for the photolysis in the acid range is represented by a sigmoid curve indicating the gradual ionization of the molecule (AH2) to ascorbyl anion (AH-). Ascorbic acid shows maximum stability around pH 5-6 due to the lowest rate of oxidation reduction of the mono--anion form. The rate of photolysis is increased up to sevenfold at pH 10.0, compared to that at pH 5.0, due to an increase in the redox potentials with pH leading to faster oxidation of the anionic species to dehydroascorbic acid in the alkaline range. The rate is very slow in the pH range 1-2 due to the existence of the non--ionized form. The apparent first--order rate constants for the photolysis of ascorbic acid at pH 1-11 range from 0.057-3.948x10-2 min-1. A scheme for the sequence of reactions involved in the photolysis of ascorbic acid is presented. [ABSTRACT FROM AUTHOR]

Aspirin (ASA) and aspirin-caffeine dosage forms are widely used as analgesic drugs. In the present study specific stability-indicating two- and three-component spectrometric methods have been developed for the assay of ASA and its degradation product, salicylic acid, in the presence and absence of caffeine (CF). The methods have been validated with respect to different parameters such as linearity, range, accuracy, precision, reproducibility, limit of detection, limit of quantification and specificity. The results indicated that the proposed methods are linear in the range of 0.0005-0.005 mg%, highly accurate (99.0-100.1%), precise (<3.0% RSD) and robust (<2.0% RSD). These methods have been applied for the assay of ASA in its thermally degraded solution and in degraded tablets. The apparent first-order rate constants (kobs) for the degradation of ASA at pH 8.0-10.0 in the absence and presence of CF are in the range of 5.37-11.0×10-3 min-1 and 4.99-10.30×10-3 min-1, respectively. The accuracy and specificity of the methods have been confirmed from the linearity of first-order plots around the assay data for the degradation of ASA. These methods can accurately determine ASA in the presence of interfering substances. [ABSTRACT FROM AUTHOR]

Fluoroquinolone antibiotics are widely used in the treatment of various infectious diseases in humans and animals. These compounds are sensitive to light and undergo photodegradation in the solid and liquid state to form a number of products which have been identified by chromatographic and spectroscopic methods. The fluoroquinolones in aqueous and organic solvents are degraded on exposure to UV and sunlight by a number of pathways depending on the reaction conditions including medium, wavelength and intensity of light and duration of exposure of the solution. The present review deals with the identification of the photoproducts, photodegradation pathways and mechanism of photodegradation of various fluoroquinolones. [ABSTRACT FROM AUTHOR]

The photoinitiated polymerization of 2-hydroxyethyl methacrylate (HEMA) (1-3 M) using camphorquinone (CQ)/triethanolamine (TEOHA) system has been studied in the pH range 6.0-9.0. The kinetics of the reaction has been evaluated during the initial stages causing about 5% HEMA conversion to avoid the effects of any variation in the volume of the solution. The change in the concentration of HEMA during polymerization has been determined by a UV spectrometric method at 208 nm with a precision of ±3%. The apparent first-order rate constants (kobs) for the polymerization of HEMA by CQ in the presence of 0.01 M TEOHA, carried out up to 100 s, range from 3.35-7.78 (1 M), 2.72-6.78 (2 M) and 2.33-5.89x10 s-1(3 M). The second-order rate constants for the interaction of TEOHA radicals with HEMA (1-3 M) range from 2.33-7.78×10-2 M-1 s-1 at pH 6.0-9.0 indicating an increase in the reactivity of TEOHA radicals with an increase in the pH of the solution. There is a linear relation between £0bs (1-3 M HEMA) and inverse of solution viscosity suggesting the quenching of CQ excited state with an increase in the viscosity of the medium. [ABSTRACT FROM AUTHOR]