Capillary electrophoresis and liquid chromatography in the analysis of some quaternary ammonium salts used in lozenges as antibacterial agents

A comparison is made of the relative merits of high-performance liquid chromatography and capillary electrophoresis, both using direct UV detection, for the determination of three quaternary ammonium compounds used as the active antibacterial ingredient in lozenge formulations. While both techniques are capable of separating the compounds cetylpyridinium chloride, dequalinium chloride, and benzalkonium chlorides, the liquid chromatographic method involving ion pairing and using a 5-mu m cyanopropyl stationary phase, was unable to resolve the benzalkonium chlorides from the lozenge excipients and quantitation was not possible. The capillary electrophoresis method using a 205-mm 50-mu m-i.d. capillary with a running buffer of 50% vol/vol 50 mM phosphate buffer at pH 3 provided superior resolution of the three antibacterials in all lozenge formulations. This system was also capable of resolving impurities in the dequalinium chloride both in the standard and in lozenges containing this compound. On the basis of quantitative results previously published, both methods have adequate validation parameters since the relative insensitivity of capillary electrophoresis compared with liquid chromatography is not important at the concentration required to be determined following a single simple sample pretreatment.