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A simple spectrophotometric method was developed for the determination of penicillamine and carbocisteine. The method depends on complexation of penicillamine with Ni, Co and Pb ions in acetate buffer pH of 6.3, 6.5 and 5.3, respectively, and carbocisteine with Cu and Ni ions in borate buffer pH of 6.7; 1-70 microg/ml of these drugs could be determined by measuring the absorbance of each complex at its specific lambdamax. The results obtained are in good agreement with those obtained using the official methods. The proposed method was successfully applied for the determination of these compounds in their dosage forms. Also, the molar ratio and stability constant of the metal complexes were calculated and a proposal of the reaction pathway was postulated.

A kinetic spectrophotometric method was developed for the determination of carbocisteine, ethionamide, thioctic acid and penicillamine based on the catalytic effect on the reaction between sodium azide and iodine in aqueous solution. Ten to 100 microg ml(-1) of carbocisteine and ethionamide, 0.1-1 microg ml(-1) of thioctic acid and 0.01-0.1 microg ml(-1) of penicillamine could be determined, respectively, by measuring the decrease in the absorbance of iodine at 348 nm by a fixed time method. The decrease in the absorbance in the first 5 min from the initiation of the reaction is related to the concentration of the drugs. The detection limits were 0.47, 0.71, 0.018 and 9.38 x 10(-4) microg ml(-1) for the four drugs, respectively. The proposed procedure was successfully applied in the determination of these drugs in pharmaceutical preparations and human serum.

A simple fluorimetric procedure was adopted for determination of three pharmaceutical compounds containing thiol groups namely, captopril, D-penicillamine and N-acetylcysteine. In this method, the drugs are treated with 1,2-naphthoquinone-4-sulfonic acid. The latter is reduced to 1,2-dihydroxynaphthalene-4-sulfonic acid which has a maximum fluorescence intensity at 480/318 nm (lambdaEm/Ex). The method is sensitive to 0.5-4.5 pg ml(- 1) with minimum detectability 0.05 microg ml(-1) (S/N = 2), and has been applied to determine these three thiols in their dosage forms. The results obtained are compared favourably with those obtained by their pharmacopeial methods.

2-Hydroxy-1-naphthaldehyde (HNA) was investigated as a derivatizing reagent for the fluorescence detection of histidine, methionine and tryptophan at 385 and 265 nm. The separation of HNA-derivatized amino acids on a conventional reversed-phase column was achieved in less than 40 min. This method was compared with the reported o-phthaldialdehyde (OPA) method. The procedure was successfully applied to the assay of the pure amino acids in a mixture and their pharmaceutical dosage forms.

Two titrimetric methods are proposed for the determination of captopril in pure form or in tablets. In the first method iodide selective electrode is used for indirect titrimetric assay of captopril. This compound forms silver salt in presence of excess silver ions, the excess silver ions are determined potentiometrically with standardized iodide solution and an iodide selective electrode. The second method involves the titrimetric determination of captopril using a new oxidimetric titrant 2.3-dichloro-5.6-dicyano-1.4-benzoquinone (DDQ) in anhydrous acetic acid. The equivalent point is detected potentiometrically using calomel and platinum electrodes. The two methods allow semimicro-determination of captopril, the results by the proposed procedures are in good agreement with those obtained by the official method.

A simple and rapid colorimetric method for the assay of amodiaquine hydrochloride, chloroquine phosphate and primaquine phosphate is described. The method is based on the interaction of the drug base with bromophenol blue to give a stable ion-pair complex. The spectra of the complex shows a maxima at 415-420 nm with high apparent molar absorptivities. Beer's law was obeyed in the concentration range 1-8, 2-10 and 2-12 micrograms.ml-1 for amodiaquine hydrochloride, primaquine phosphate and chloroquine phosphate respectively. The proposed method was applied to the determination of these drugs in certain formulations and the results were favourably comparable to the official methods.

A first derivative (1D) spectrophotometric method is described for the determination of furazolidone in the presence of its degradation product (5-nitrofuraldehyde). The method was based on the direct measurement at the maximum of the first derivative curve for furazolidone at 390 nm, which is the zero crossing point of 5-nitrofuraldehyde thus avoiding interference from the degradation product. 5-Nitrofuraldehyde was determined after thin-layer chromatographic separation using silica gel G254 as the coating substance, and mixture of toluene and 1.4-dioxan (95:5) as the developing system. After separation, furazolidone content and its degradation product, 5-nitrofuraldehyde, could be determined separately by first-derivative spectrophotometry at 390 and 290 nm, respectively. 2.5-25 micrograms ml-1 of furazolidone and 5-nitrofuraldehyde could be determined by this method with good accuracy. The proposed method was successfully applied to determine furazolidone in its tablets and 5-nitrofuraldehyde in expired tablets. The results obtained were in good agreement with those obtained by the official method.

Two methods are proposed for the determination of isoniazid in pure form or in tablets. In the first method chlorpromazine hydrochloride, when treated with 2-iodoxybenzoic acid as an oxidant in 50% w/v o-phosphoric acid solution, is oxidized to chlorpromazine free radical which absorbs at 530 nm. The red free radical is readily reduced quantitatively by isoniazid to the colourless chloropromazine. The addition of isoniazid to a red solution of chlorpromazine free radical results in a decrease in absorbance in direct proportion to the quantity of isoniazid. This forms the basis for the quantitative determination of micro-quantities of isoniazid (3-18 micrograms ml-1). The second method involves the titrimetric determination of isoniazid using N-bromophthalimide as a titrant. The end-point is determined either directly using methyl red or amaranth as indicator, or by a back titration method in which a known excess of N-bromophthalimide solution is added to isoniazid solution and then the residual unreacted reagent is determined iodometrically. The results by the proposed procedures were in good agreement with those obtained by the official methods.

An indirect titrimetric method is described for the determination of chlorprothixene, methixene and thiothixene. A known and excessive volume of 2-iodylbenzoate is added and after a specified time the surplus is determined iodometrically. The method has been applied to the analysis of pharmaceutical preparations containing these drugs and the results obtained compare favourably with those from the pharmacopoeial methods. The method is simple, accurate and precise.