Oxidized diphenylamine as a spectrophotometrec reagent for the determination of some pharmaceutical thiols and thioamides

Oxidized diphenylamine is newly utilized as a redox spectrophotometric reagent for the determination of six pharmaceutically important thiol and thioamide drugs named: acetylcystiene, captopril, carbimazole, propylthiouracil, thiopental sodium, and tiopronin. The method is based on measurement of the decrease in absorption intensity of the oxidized diphenylamine [diphenylbenzidine violet, lambda max = 580 nm] reagent as a result of the reduction effect of the analysed drugs This reagent was instantaneously prepared by the oxidation of diphenylamine using ferric sulphate in sulphuric acid medium. The molar ratio of the chromogen reagent was determined to be 2:1; diphenylamine: iron [III]. The decrease in colour intensity was found to be quantitatively dependent on drug concentration. Experimental variables including reagent concentration, acid type and concentration, dilution solvent, reaction time, temperature and stability were studied and optimized. Validation parameters including linearity range, detection and quantitation limits, precision, selectivity and robustness were evaluated. The proposed method was found to be simple, sensitive and accurate one indicated by the studied validation parameters. Good recoveries [98.0 +/- 0.14 - 100%, +/- 0.98] were obtained by the suggested method and it was applied for the determination of the studied drugs in many pharmaceutical dosage forms available in the local market. Good agreement, indicated by acceptable t- and F- tests, was found between results obtained by the suggested method and those obtained by the reported or pharmacopoeial methods

Spectrophotometric determination of piroxicam using 2,2-diphenyl-1-picrylhydrazyl1]

An indirect spectrophotometric method has been developed for the determination of piroxicam by interaction with 2,2-diphenyl-1-picrylhydrazyl [DPPH]. The DPPH reagent is an intense violet-colored stable free radical which is discolored on reaction with the drug. The decrease in violet color is used as measure of the quantity of the drug present. Beer's Law is obeyed in the concentration range of 2-20 mug of piroxicam per ml [sigma max = 1.66 x 10 4 mol -1 cm -1]. No interference occurred by the degradation product of the drug [2-aminopyridine] or the common excipients in pharmaceutical preparations. A reaction pathway was suggested and verified by the synthesized piroxicam cyclodehydration product. The structure of the latter compound was confirmed by TLC, IR and PMR spectroscopy

HPLC and spectrophotometric determination of nifuroxazide and its pharmaceutical formulations

Two methods for the quantitative determination of nifuroxazide are described. The first method is based on the HPLC separation of the compound with an ODS reversed phase column using acetonitrile-water [40:60] as mobile phase and spectrophotometric detection at 380 nm. Accelerated stability tests in direct sun light and at elevated temperature were carried out. The second one is a spectrophotometric procedure based on the interaction of the drug with tetraethylammonium hydroxide [TEAH] in dimethylsulphoxide [DMSO] medium at 20 +/- 5C to produce a blue product. The quantitation of the product was carried out at 610 nm [molar absorptivity 2.99 x 104 1 mol-1 cm-1]. A linear correlation was found between absorbance at lambda max and concentration of nifuroxazide in the range 0.5-9.0 mugml1. The two proposed methods were used for the determination of nifuroxazide powder and its dosage form. Both methods are rapid, accurate, precise and their results were comparable with the X-th French pharmacopoeial procedure

Quantitation of floctafenine by high pressure liquid chromatography [HPLC] and spectrophotometric methods

Two methods for the quantitative determination of floctafenine are described. The first, a spectrophotometric procedure, is based on the formation of a red Schiff-base between floctafenine and p- dimethylaminocinnamaldehyde [p-DAC] after reduction with zinc powder and hydrochloric acid in ethanol acidic medium at room temperature. At the maximum absorption of 541 nm, Beer-Lambert's Law was adhered to over the 1-9 mug/ml range [epsilon max 3.99 x 10 4 l/mol/cm]. The second method involved the application of HPLC, C-18 column, with a mobile phase consisting of 82.5: 17.5 methanol: water at a flow rate of 1 ml/min. Samples dissolved in methanol were estimated by the measurement of peak height using UV detection at 254 nm. The results obtained with the two proposed methods revealed their successful application for the quantitative estimation of floctafenine in bulk drug and as tablets with good accuracy and precision

Spectrophotometric method of the determination of penicillamine and its dosage form

A sensitive and precise spectrophotometric method has been developed for the determination of penicillamine. It depends on the reaction of penicillamine with an excess of 2,2-diphenyl-1-picrylhydrazyl [DPPH] in aqueous methanolic medium. The amount of consumed reagent was found to be proportional to the concentration of the drug. All measurements were carried out at 520 nm in the presence of acetate buffer [pH = 4] at room temperature [20 +/- 2C]. Beer's law was obeyed in the concentration range 2-10 mug/ml [epsilon max = 0.93 x 104 l.mol -1.cm -1]. The proposed method was applied for the determination of penicillamine in pure form and in pharmaceuticals. The results obtained were in concordance with those of the official procedure

Spectrophotometric determination of phenylephrine hydrochloride in multi-component pharmaceutical preparations with fast violet B salt

A spectrophotometric method for the determination of phenylephrine hydrochloride is descried. The method involves formation of an intense red complex [lambda max 520 nm] due to reaction of the drug with zinc chloride salt of 4-benzoylamino-2-methoxy-5-methylbenzenediazonium chloride [fast violet B salt] in acidic medium. Beer's Law is obeyed over the concentration range 1-10 mug/ml of phenylephrine hydrochloride with a molar absorptivity of 2.03 x 10 4 l.mol -1 cm -1. The optimum conditions for full color development have been investigated. The proposed method has been applied to the analysis of some pharmaceutical preparations with good recoveries [98.8-101.2%]. No interference took place by common excipients, dyes and other drug compounds, likely to be present in preparations

Spectrophotometric determination of some pharmaceutical pyrazolidineone derivatives using diphenylpicrylhydrazyl

A spectrophotometric procedure for the determination of phenylbutazone, oxyphenbutazone and sulfinpyrazone using 2, 2-diphenyl-1-picrylhydrazyl is described. The reagent is an intense violet and stable free radical which becomes discoloured on reaction with the investigated pyrazolidinedione derivatives. The decrease in violet colour is proportional to the drug concentration. All measurements are carried out at 520 nm using ethanolic solutions of the drugs and reagent in the presence of acetate buffer [pH=5-6]. Beer's law is obeyed in the concentration ranges; 2-20 mcg/ml [for phenylbutazone], 2-15 mcg/ml [for oxyphenbutazone] and 5-40 mcg/ml [for sulfinpyrazone]. The accuracy varies between 100.1 +/- 0.64% for phenylbutazone, 99.7 +/- 0.60% for oxyphenbutazone, and 100.0 +/- 0.68% for sulfinpyrazone. The proposed method is successfully applied to the determination of the three bulk drugs and tablets of phenylbutazone and oxyphenbutazone. The results are in good agreement with those of the official B.P.. 1988 and U.S.P. XXI methods