Analysis of some commercial preparations for migraine treatment using ion-pair high-performance liquid chromatography with addition of salts to the mobile phase

Abstract

When appropriate salts are added to the mobile phase in ion-pair high-performance liquid chromatography (HPLC) it is possible to arrive at an isocratic solvent with which complex mixtures of nitrogenous compounds of different p K a values and lipophilic characteristics may be separated. Selectivity in the manipulation of solute retention depends on the salt type, its concentration, the percentage of organic modifier in the mobile solvent and the solute itself. In addition to a dramatic reduction in analysis time, the use of salts can also improve the resolution of closely eluted peaks. With judicious control of the pH of the mobile solvent, the addition of salts to the mobile phase can cause the retention of compounds of different p K a values to alter in a contrasting manner. Under typical ion-pair HPLC conditions, an increase in salt concentration in the mobile solvent enhances the retention of neutral compounds and reduces the retention of ionized compounds. An inverse log—log relationship between the capacity factor of a solute and the salt concentration in the mobile phase was found. Examples are given of the use of salts in mobile solvents for ion-pair HPLC of a number of pharmaceutical preparations employed for the treatment of migraine.