H. Abdine

Spectrophotometric and spectrofluorometric methods for the assay of lisinopril in single and multicomponent pharmaceutical dosage forms

Simple and sensitive methods are described for the assay of lisinopril in tablets. The first method (A) is based on the reaction of the drug with chloranil in aqueous solution of pH 9.5 to give yellow colour measured at 346 nm. The second method (B) is based upon the interaction of lisinopril with dichlone resulting in the formation of an intense purple colour measured at 580 nm. The third method (C) depends on the reaction of the drug with acetylacetone and formaldehyde to form a coloured condensation product measured at 356 nm and also has a strong fluorescence at 475 nm (lambda(ex) 410 nm). This method is extended to determine lisinopril in binary mixtures with hydrochlorothiazide. The last method (D) depends on measuring the first and second derivative spectra of lisinopril. Moreover, the derivative method is used as stability-indicating method where lisinopril can be determined in presence of its degradation products. The proposed methods proved to be suitable for a rapid quality control of commercial dosage forms. The results obtained were precise and accurate.

Spectrophotometric methods for the determination of benazepril hydrochloride in its single and multi-component dosage forms

Three sensitive and accurate methods are presented for the determination of benazepril in its dosage forms. The first method uses derivative spectrophotometry to resolve the interference due to formulation matrix. The second method depends on the color formed by the reaction of the drug with bromocresol green (BCG). The third one utilizes the reaction of benazepril, after alkaline hydrolysis, with 3-methylbenzothialozone (MBTH) hydrazone where the produced color is measured at 593 nm. The latter method was extended to develop a stability-indicating method for this drug. Moreover, the derivative method was applied for the determination of benazepril in its combination with hydrochlorothiazide. The proposed methods were applied for the analysis of benazepril in the pure form and in tablets. The coefficient of variation was less than 2%.

Spectrophotometric determination of acetaminophen and salicylamide through nitrosation and subsequent chelation

A nitrosation reaction has been adopted for the spectrophotometric determination of acetaminophen and salicylamide. The selectivity of the reaction is increased through utilisation of the nitroso derivatives as chelating agents for cobalt(II) and copper(II) ions. The optimum experimental conditions for the application of nitrosation and nitrosation with subsequent chelation were established. The proportions of reactants in each method and the instability constants for the products were determined. The nitroso derivatives and their chelates obey Beers law and their absorbances were used for the determination of acetaminophen and salicylamide in pharmaceutical formulations. The proposed methods gave more accurate results than the official methods.

Application of orthogonal functions to spectrophotometric analysis of weakly absorbing compounds in tablets.

Glenns method of orthogonal functions has been applied to correct for irrelevant absorption during the analysis of tablets of chlorpheniramine maleate, phenyltoloxamine dihydrogen citrate, diphenhydramine hydrochloride and ephedrine hydrochloride. The results suggest that the method can be used for routine analysis.

Spectrophotometric Determination of Enalapril Maleate and Ramipril in Dosage Forms

Abstract Three sensitive and accurate spectrophotometric methods have been developed for the assay of enalapril maleate and ramipril, each in its dosage forms. These methods depend on the reaction of the drugs with p-chloranilic acid, the reaction with picric acid, and the ion-pair salt formation with bromocresol green. The proposed methods have been applied to the analysis of these drugs in their commercial tablets. The results obtained were precise and accurate.

Spectrophotometric and Spectrofluorimetric Methods for the Determination of Terazosin in Dosage Forms

Abstract Five simple and accurate methods are presented for the determination of terazosin (TZ) in tablets. These methods are based on: the direct measurements of the first and second derivative spectra of samples (A), the reaction of TZ with chloranil (CH) in aqueous solution of pH 9 to give an intense yellow color measured at 340 nm (B), the reaction of the drug with mercurochrome (MER) in aqueous alkaline medium to give an intense red color measured at 543 nm (C), the formation of an ion-pair salt between the drug and bromocresol purple (BCP) with subsequent absorbance measurements at 412 nm (D), and a sensitive fluorimetric method (E). The latter method was extended to determine TZ in presence of its degradation products.

Simultaneous determination of tenoxicam and 2-aminopyridine using derivative spectrophotometry and high-performance liquid chromatography

Derivative spectrophotometry and high-performance liquid chromatography (HPLC) were used to determine tenoxicam and one of its decomposition products (2-aminopyridine) simultaneously and in the presence of each other. The derivative procedure was based on the linear relationship between the tenoxicam concentration and the second derivative amplitudes at 390-348 nm (peak-to-trough) measurement. The 2-aminopyridine was determined through measuring the second derivative amplitude at 241 nm (zero-crossing for tenoxicam). For the HPLC procedure, a reversed-phase C8 column with a mobile phase composed of 0.02 M sodium acetate-methanol-acetonitrile (11:8:1) with 0.005 M heptane sulfonic acid sodium salt, as an ion pair, was used to separate both compounds with 2,4-dinitrochlorobenzene, as an internal standard, in reasonable time. The flow rate was 1.5 ml min-1 with a programmable ultraviolet (UV) detection at 300 and 375 nm. Both UV derivative spectrophotometric and HPLC approaches were followed for confirming the purity of tenoxicam in bulk and tablets dosage form.

Spectrophotometric and HPLC determination of secnidazole in pharmaceutical tablets.

Simple and accurate spectrophotometric and HPLC methods were developed for the determination of secnidazole in tablets dosage form. The first spectrophotometric method depends on the reduction of secnidazole molecule with zinc dust and hydrochloric acid followed by condensation with either p-dimethylaminobenzaldehyde or anisaldehyde to give colored chromogens having absorbance at 494 and 398 nm, respectively. The second method was based on the reaction of the drug with sodium nitroprusside in the presence or absence of hydroxylammonium hydrochloride. The formed colored chromogens were measured at 584 and 508 nm, respectively. The experimental conditions were optimized and Beers law was obeyed over the applicable concentration ranges. The application of HPLC procedures depended on using either a conventional or microbore reverse-phase (C18) column along with mobile phases consisting of water and methanol (30:70), at pH of 3.5. Both techniques were applied successfully for the analysis of secnidazole in tablets form. The results obtained from both procedures were statistically compared using the Students-t and F-variance ratio tests.

Simultaneous determination of melatonin-pyridoxine combination in tablets by zero-crossing derivative spectrophotometry and spectrofluorimetry.

Two methods have been developed for the analysis of melatonin (M) and pyridoxine hydrochloride (PH) in combination. The first method depends on first- and second-derivative ultraviolet spectrophotometry, with the zero crossing technique of measurement. First-derivative amplitudes at 296 nm and second-derivative amplitudes at 294 and 322 nm are selected for the determination of M and PH, respectively. The second method is based on the native fluorescence of both M and PH, in methanol and 0.1 M hydrochloric acid, respectively, after a preliminary solvent extraction procedure. The relative standard deviation of both methods was less than 2.0%. The two methods have been successfully applied to the determination of both drugs in laboratory-prepared mixtures and in tablets.

Application of orthogonal functions to correct for quadratic irrelevant absorption in spectrophotometric analysis

The seven‐point correction method of Ashton and Tootill has been examined. The method is generalized for other groups of points from n = 5 to n = 14. Glenns method of orthogonal functions proved to be suitable for assaying cyclandelate in the presence of interference with quadratic curvature.