Determination of phenolphthalein and methylene blue by first derivative spectrophotometry and potassium nitrate by direct spectrophotometry in a pharmaceutical formulation

Abstract

A rapid first derivative visible spectrophotometric determination is described for the simultaneous determination of phenolphthalein (PHP) and methylene blue (MB) in the presence of potassium nitrate (KNO3). Potassium nitrate is also determined by direct visible spectrophotometric method in the presence of phenolphthalein and methylene blue without any interference. The methods have been applied to the determination of the three compounds in a commercial dosage form. The calibration graphs were linear in the range of 0.30-3.20 mg mL-1 for MB and 0.80-3.18 micrograms mL-1 for PHP and 0.80-8.10 micrograms mL1 for KNO3. The specificity, accuracy and precision of the methods have been assessed.