Phenylephrine is a hydrophilic basic compound. Phenylephrine is used primarily as a decongestant in cough composition. Tannic acid is poly-phenolic compound. Tannic acid is also used to produce tannate salts of certain antihistamins and anti-tussives to impart increased stability or slow release properties to the API (active pharmaceutical ingredient). Phenylephrine in the presence of tannic acid is analyzed by mixed-mode HPLC on a Primesep 100 column. Retention time for phenylephrine is controlled by the amount of acetonitrile and buffer concentration. Tannic acid elutes closer to void and not interferes with analysis of phenylephrine. Method can be used with UV, ELSD, CAD or LC/MS detection.