NEGATIVE-ION ELECTROSPRAY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY METHOD DEVELOPMENT FOR DETERMINATION OF A HIGHLY POLAR PHOSPHONIC ACID SULFONIC-ACID COMPOUND IN PLASMA - OPTIMIZATION OF AMMONIUM ACETATE CONCENTRATION AND IN-SOURCE COLLISION-INDUCED DISSOCIATION

A method, based on negative ion electrospray ionization(ESI) single-st age mass spectrometry coupled with HPLC, was developed for the determi nation of a squalene synthase inhibitor, BMS-187745, in human plasma. BMS-187745, a highly polar compound with both phosphonic acid and sulf onic acid groups, presented difficulties in developing plasma extracti on and HPLC procedures. Precipitation of the plasma protein with metha nol was finally chosen as the basis for sample preparation since extra ction with water-immiscible solvents or with solid-phase extraction co lumns failed. It was essential to add ammonium acetate to the HPLC mob ile phase, not only to enhance the retention of BMS-187745 but also to ensure a well-shaped chromatographic peak. While the use of ammonium acetate had the desired chromatographic effects, it had the undesirabl e consequence of suppressing the negative ion ESI signal. With the pla sma extracts, the [M-H2O-H](-) ion (m/z 367) showed significantly lowe r chemical noise than the [M-H](-) ion (m/z 385), and was thus chosen as the analytical ion for the selected ion monitoring. The signal of t he m/z 367 ion was significantly enhanced by the optimization of the i n-source collision-induced dissociation (CID) of m/z 385 to m/z 367. ( C) 1997 Elsevier Science B.V.