Dihydralazine sulfate analysis using 2-methyl-o-nitropyridine-6-carboxaldehyde.

A sensitive, selective colorimetric assay was developed for the quantitative analysis of dihydralazine sulfate. The method is based on the interaction of buffered (pH 4) dihydralazine sulfate with a methanolic solution of 2-methyl-3-nitropyridine-6-carboxaldehyde upon heating to give an orange color. This color can be quantified spectrophotometrically at 450 nm,with a lower limit of detection of 1 mug/ml. The color is stable for at least 24 hr. There is no interference from other drugs likely to be present along with dihydralazine sulfate and common excipients. The method was used successfully for the determination of dihydralazine sulfate in combination with other drugs in different commercial tablets. The developed method was applicable as a stability-indicating assay.

Rapid and sensitive colorimetric determination of cobalt(II).

A highly selective and sensitive spectrophotometric determination of cobalt (II) was developed. 7-Nitroso-8-hydroxyquinoline-5-sulfonic acid sodium salt was used as the chromogenic reagent for color development. Although other metals form colored chelates with the ligand, it was possible to develop a selective method using McIlvaine's pH 8 citric acid-phosphate buffer. Under these conditions, iron(II), iron (III), copper (II), zinc (II), and manganese (II), minerals likely to be compounded with cobalt (II) in geriatric formulations, do not interfere with the precision of the method or the color development. Calcium (II) and magnesium (II) do not form colored chelates with the used ligand. Hormones, vitamins, and additives likely to be present along with the cobalt ion in pharmaceutical formulations do not interfere. The sensitivity is 0.37 mug of cobalt (II)/ml of sample solution.

Rapid, sensitive colorimetric method for determination of ethinyl estradiol.

A colorimetric procedure, based on the formation of an azo dye by condensation of diazotized 5-chloro-2,4-dinitroaniline with ethinyl estradiol, was developed. An alkaline solution of ethinyl estradiol is reacted with the reagent, and the resulting color is measured at 450 nm. Absorbance versus concentration is linear up to 10 mug/ml; the lower limit of detection is 1 mug/ml under the conditions studied. Replicate analysis showed good agreement, and an average recovery of 99.6 +/- 0.3% was obtained for analyses of synthetic mixtures. Vitamins and minerals likely to be present along with ethinyl estradiol in certain geriatric formulations, as well as ordinary tablet excipients and coating materials, do not interfere with the precision of the method or development of the color. The method is applicable to progestin-estrogen preparations. Assay results on various single-component as well as contraceptive commercial samples are reported.