Titrations of barbiturates and sulfa drugs in 3-methyl-2-oxazolidone

Use of p-benzoquinone for the spectrophotometric determination of certain sulphonamides

A simple spectrophotometric method for the determination of 15 sulphonamides in bulk and in dosage forms is described. The method is based on the interaction of p-benzoquinone with sulphonamides in 0.1 M hydrochloric acid. The resulting chromophore is measured at 500 nm. The effects of different variables on colour development were established. Beer's law was obeyed in a concentration range of 10-50 micrograms ml-1. Results from the analysis of different sulphonamide tablets and ophthalmic solutions marketed locally were in good agreement with that of a reference method. Correlations between A1cm(1%) and certain physical parameters such as pKa values, characteristic volume Vx, and molecular connectivity indices 1X and 1Xv were determined by linear regression equations. A poor correlation was found between A1cm(1%) and bulkiness parameters but a highly significant negative correlation was obtained with apparent pKa values.

Short communication

A simple and rapid calorimetric method for the determination of 10 sulphonamides as single entities and sulphamethoxazole in combination with trimethoprim without prior separation was developed. The method is based on the reaction of sulphonamide with phenothiazine and N-bromosuccinimide at pH 6 to produce a blue coloured product after acidification. The chromogen for all the sulphonamides was measured at 605 nm. The effect of several variables on colour development (concentration of phenothiazine and N-bromosuccinimide, time, pH) were established. Beer's Law was obeyed for all the drugs. The method was successfully applied to the analysis of single component sulphonamide tablets and ophthalmic solutions, with average results of labelled claim of 96.7 +/- 0.95 to 100.67 +/- 1.2. A good correlation was observed between molar absorptivities and pK(a) values of the sulphonamides (r = 0.9005).