Mohamed E. Abdel-Hamid

Utility of 2,3-dichloro-5,6-dicyano-p-benzoquinone in assay of codeine, emetine and pilocarpine

A simple and sensitive spectrophotometric method for the assay of codeine, emetine and pilocarpine is described, based on the interaction of these drugs (as n-electron donors) with 2,3-dichloro-5,6-dicyano-p-benzoquinone (as pi -acceptor) to give a highly coloured radical anion which exhibits maximum absorption at 460 nm. Formation of the radical anion has been established by electron spin resonance measurements. Beers law is obeyed for the alkaloids investigated. The assay results are in accord with pharmacopoeial assay results. The procedure is sufficiently sensitive to permit unit dose assay of the individual alkaloids in pharmaceutical formulations.

Spectrophotometric Determination of Some Tranquillizers and Antidepressants Using 2,3-Dichloro 5,6-Dicyano-p-Benzoquinone

Abstract A simple and sensitive spectrophotometric method is described for the assay of some tranquillizers and antidepressants, namely, chlorpromazine, imipramine, amitriptyline and chlorprothexine. The method was based on the interaction of these drugs as n-electron donors with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as λ -acceptor to give a highly coloured radical anion which exhibits maximum absorption at 460 nm. The radical anion was proved by electron spin resonance measurements. The proposed method has been successfully applied for the determination of the examined drugs in tablets. The assay results were in accord with the pharmacopoeial results.

Determination of diazepam and oxazepam using high-performance liquid chromatography and fourth-derivative spectrophotometric techniques

Accurate and very precise HPLC and fourth-derivative ultraviolet spectrophotometric methods for the determination of diazepam and oxazepam in dosage forms are described. The methods are capable of distinguishing the intact drugs from their hydrolytic degradation products at 6 M hydrochloric acid. Mean recoveries for mixtures containing the drugs and their degradation products were found to be 101.3 ± 2.5 and 101.4 ± 1.8% using the HPLC procedure and 100.8 ± 2.0 and 101.0 ± 2.7% using the fourth-derivative spectrophotometric technique for diazepam and oxazepam, respectively. The reported procedures have been successfully applied to monitoring either diazepam or oxazepam in pharmaceutical formulations.

Use of p-chloranilic acid for the colorimetric determination of some antimalarials

A simple and sensitive colorimetric method for the assay of quinine sulphate, primaquine diphosphate, amodiaquine hydrochloride and pyrimethamine is described. The method is based on the interaction of the drugs and p-chloranilic acid to give a stable product with an intense colour which can be used for the determination of these antimalarials in their pharmaceutical preparations.

Application of Difference and Derivative Ultraviolet Spectrometry for the Assay of Some Benzodiazepines

Abstract Differential (δ A), second derivative (D2) and differential second derivative (δ D2) ultraviolet spectrophotometric methods have been described for the quantitiative estimation of clonazepam, diazepam and medazepam in pharmaceutical formulations such as drops, tablets and capsules. Interferences due to excipients and diluents are thereby avoided. Accuracy of the analyses with the proposed procedures is significantly greater than the conventional spectrophotometric and official methods.

Colorimetric determination of two fenamates in capsule dosage form

The colorimetric determination of mefenamic acid and flufenamic acid with potassium ferricyanide in sodium hydroxide medium is described. The orange product is measured at 464 nm. The molar absorptivities are 1.9 x 10(3) and 2.9 x 10(3) 1.mole(-1).cm(-1) for mefenamic acid and flufenamic acid, respectively. The method has been applied successfully to the determination of these drugs in capsules.

A stability–indicating first–derivative spectrophotometric assay of acetazolamide and its use in dissolution and kinetic studies

A simple, rapid, stability–indicating first–derivative spectrophotometric assay procedure for the determination of the degradation products of acetazolamide is described. The dissolution and kinetics of drug degradation in aqueous buffered solutions were studied using the proposed method. Acetazolamide solution exhibited optimum stability at pH 4. The influences of temperature and sonic energy on the degradation of acetazolamide in 0–01 M NaOH solution were also studied. The results showed first–order reaction kinetics, with a degradation rate constant and degradation half–life of 31 times 10‐3 day‐1 and 8–23 days, respectively.

Spectrophotometric determination of ascorbic acid and thiamine hydrochloride in pharmaceutical products using derivative spectrophotometry

Direct spectrophotometric methods for the determination of ascorbic acid (vitamin C) and thiamine hydrochloride (vitamin B1) each in the presence of its degradation product are presented. The methods are based on the use of UV derivative spectrophotometric measurements—the first derivative at 215 nm for ascorbic acid and the second derivative at 254 nm for thiamine hydrochloride. The values obtained are linearly related to the concentration of each vitamin solution and have relative standard deviations of 0.52 and 1.07%, respectively. The mean percentage recoveries for mixtures of each vitamin with their respective degradation product were found to be 101.5 and 99.4%, respectively. Graphs of log C(%m/V)versus time for ascorbic acid solution in 3 N hydrochloric acid and for thiamine hydrochloride solution in buffer at pH 10 were straight lines with slopes of –0.1044 d–1 and –0.0207 h–1, respectively. The methods have been successfully applied to monitor the stability of the vitamins.

Comparative Spectrophotometrc Analysis of Rifampicin by Chelate Formation and Charge-Transfer Complexation

Abstract Simple, rapid, and accurate spectrophotometrc procedures for the determination of the antibiotic rifampicin, in capsules, are presented. A chelate formation of the antibiotic with cupric ion and charge-transfer complexation with halogenated quinones are carried out. Linear correlations between absorbance and concentration over the range of 40-100 μg ml−1 were computed. The reaction pathways were proposed. The utility of copper chelate as a stability indicating procedure as well as a method to determine rifampicin In spiked urine samples is demonstrated.

Spectrophotometric determination of chloramphenicol using orthogonal polynomials.

A direct spectrophotometric method using combined orthogonal polynomials (PW) for the determination of chloramphenicol in the presence of its alkali-induced degradation products is described. Mixtures of the intact drug with its degradation products were prepared and their absorbances were measured over the wavelength range 248–314 nm. The pW coefficient calculated over this range at 6-nm intervals was found to be reproducible and independent of the degradation products. The proposed method proved to be applicable to monitoring chloramphenicol stability.