REVERSED-PHASE ION-PAIR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY OF PHOSPHATIDYLINOSITOLS

Reversed-phase ion-pair high-performance liquid chromatographic (HPLC) separations of molecular species of phosphatidylinositols (PI) were studied. Mobile phases of acetonitrile-methanol-water containing various tetraalkylammonium phosphates (TAAP) were used for optimization. Stationary phases of macroporous polystyrene divinylbenzene (MPD), octylsilica, and octadecylsilica exhibited varying degrees of retentivity toward PI solutes. Without exception, capacity factors (k') of PI on either alkylsilica or MPD increased with the alkyl chain length and the concentration of the quaternary ammonium counter ions evaluated. The results can be interpreted in terms of an ion-pair retention mechanism. Logarithmic k' values were linearly related to the total number of carbons in TAAP. Perbenzoylation of PI yielded derivatives readily resolvable without the use of any mobile phase additive. Incorporation of TAAP to a mobile phase facilitated component separations of early-eluting perbenzoates. In HPLC with MPD, hydrophobic interactions of the perbenzoate analytes with the stationary phase appeared to arise from the nonpolar tail groups of PI molecules. Potential applicability of the reversed-phase ion-pair HPLC method for analysis of molecular species of PI in soybean oil is demonstrated.