Applications of paired ion high-pressure liquid chromatography: quantitative determination of potassium guaiacolsulfonate and other ingredients in cough syrups.

A method for the quantitative determination of potassium guaiacolsulfonate and phenylephrine hydrochloride in commercial dosage forms was developed. The method is based on paired ion high-pressure liquid chromatography with tetrabutylammonium as the counterion. The method not only separates potassium guaiacolsulfonate from phenylephrine hydrochloride but also from some other ingredients: chlorpheniramine maleate, sodium benzoate, colors, and flavors. Furthermore, two isomers of potassium guaiacolsulfonate, potassium salts of 4- and 5-guaiacolsulfonic acid, also separate from each other. The method was tried on five different commercial dosage forms (all with different colors) with excellent results on three. In the other two samples, which also contained codeine, three may have been a stability problem.