Determination of linsidomine in human plasma by tandem LC-MS with ESI

A sensitive method for the determination of linsidomine in plasma was devel oped. using high-performance liquid chromatographic (HPLC) separation with tandem mass spectrometric detection. Linsidomine was derivatised with propy l chloroformate and extracted with tert-butyl methyl ether/1,2-dichloroetha ne (55:45, v/v), back-extracted into HCl (0.01 M) followed by alkalinisatio n and back-extraction into ether; the final ether extract evaporated, recon stituted in mobile phase and then separated on a Phenomenex(R) Luna Cls (2) 5 mu 2.1 x 150 mm column with a mobile phase consisting of methanol-water- formic acid (98/100%) (400:600:0.05, v/v/v) at a flow-rate of 0.4 mi min(-1 ). Detection was achieved by a Finnigan MAT mass spectrometer (LCQ) at unit resolution in the selected reaction monitoring (SRM) mode monitoring the t ransition of the protonated molecular ion m/z 257.0 to the product ion m/z 86.0. The mean recovery for linsidomine was 51% with a lower limit of quant ification of 0.70 ng/ml using 1 mi plasma for extraction. This LC-MS/MS met hod for the determination of linsidomine in human plasma allows for better specificity and a higher sample throughput than the traditional LC-UV metho ds. It also demonstrates the profound effect that the composition of acidic modifiers and matrix constituents can have on the electrospray ionisation (ESI) of the analyte. (C) 2000 Elsevier Science B.V. All rights reserved.