Reversed-phase separation of basic tricyclic antidepressants using buffered and fluoroform-enhanced fluidity liquid mobile phases

In an effort to expand the range of applications of enhanced-fluidity liquid chromatography (EFLC) to strongly polar and basic analytes, fluoroform (CHF3) was investigated as a fluidity-enhancing agent. Fluoroform was chosen due to its high polarity, low viscosity and chemical inertness toward water and basic analytes. A group of representative basic compounds, tricyclic antidepressants, covering a wide range of polarity was chosen as model compounds. Their retention behavior on a C18 stationary phase in methanol/phosphate buffer and methanol/phosphate buffer/CHF3 mobile phases was characterized. The chromatographic performance with mobile phase conditions of different pH, with and without CHF3 addition and with addition of triethylamine was studied. The advantages of using CHF3 enhanced and buffered mobile phases were shown in the much improved chromatographic performance, such as shortened analysis time, increased efficiency, lower pressure drop and improved selectivity. Furthermore, this study demonstrated for the first time, that a commercial instrument could be readily utilized for EFLC separations which greatly expands the application range of the EFLC technique and chromatographic instrumentation.