Assaying Antacids for Neutralizing Capacity with Different Indicators

Abstract

Antacids have been assayed titrimetrically for their neutralizing capacity using copper sulfate, methyl orange and methyl red as indicators of equivalence points. End-point with copper sulfate is marked with the appearance of a stable bluish-white turbidity. Estimated values (mL 1 N acid consumed per 100 mg antacid base) with copper sulfate did not differ from those obtained with methyl orange (P > 0.1). The values obtained with methyl red were significantly lower than those obtained with either copper sulfate or with methyl orange for those preparations containing aluminum as common cationic species (P < 0.05) and for others were not significantly different (P > 0.1). Investigations reveal that choice of indicators affects estimated values and copper sulfate is a valuable substitute to methyl orange for assaying antacids for neutralizing capacity. Copper sulfate offers obvious advantages, provides stable end-point and is suitable for measuring titratable acidity of coloured solutions.