Preliminary Study on the Use of Water-in-Oil Microemulsion Eluents in HPLC

This paper describes the use of water-in-oil (W/O) microemulsion eluents to achieve unique normal phase HPLC separations. The effects of varying the oil type, co-surfactant, surfactant, use of mixed surfactant and water concentration upon the chromatographic performance was assessed. Other parameters such as temperature and flow rate were also investigated. An optimised set of W/O microemulsion HPLC (MELC) operating conditions was then applied to the separation of a range of acids, bases and neutral compounds. The more water soluble compounds were more highly retained. W/O MELC was found to be especially suitable for determination of water insoluble compounds. The drug content in bumetanide tablets was determined by W/O MELC with good linearity and accuracy. The solubilising ability of the W/O microemulsion reduced sample preparation (precipitation and extraction) requirements compared to conventional HPLC. The results obtained compared well with those obtained by a validated reverse phase HPLC method. It is recommended that W/O MELC should be considered for routine applications, especially for the analysis of water insoluble compounds in complex sample matrices. Further research is recommended to more definitely assess the operating parameters of W/O MELC and to determine other applications.