Determination of a cyclic hexapeptide, a novel antifungal agent, in human plasma by high-performance liquid chromatography with ion spray and turbo ion spray tandem mass spectrometric detection

Methods for the determination of a semi-synthetic cyclic hexapeptide (I, MK -0991) in human plasma based on high-performance liquid chromatography (HPL C) with tandem mass spectrometric (MS-MS) detection using pneumatically ass isted electrospray (ion spray, ISP) and turbo ion spray (TISP) interfaces w ere developed. Drug and internal standard (II, an isostere of I) were isola ted from plasma by solid-phase extraction (SPE). The eluent from SPE was ev aporated to dryness, the residue was reconstituted in mobile phase and inje cted into the HPLC system. The use of ISP, TISP and heated nebulizer (HN) i nterfaces as sample introduction systems were evaluated and showed that the heated nebulizer was not adequate for analysis due to thermal instability and/or adsorption of I and II to glass surfaces of the interface. Compounds I and II were chromatographed on a wide pore (300 Angstrom), 150x4.6 mm C- 8 analytical column, and the HPLC how-rate of 1.2 ml/min was split 1:20 pri or to introduction to the ISP or TISP interface of the mass spectrometric s ystem. The MS-MS detection was performed on a PE Sciex API III Plus tandem mass spectrometer operated in selected reaction monitoring mode (SRM). The precursor-->product ion combinations of mit 1093.7-->1033.6 and 1094.7-->10 33.6 were used to quantify I and II, respectively, after chromatographic se paration of the analytes. The assay was validated in the concentration rang e of 10-1000 ng/ml using ISP, and 2.5-500 ng/ml of plasma using TISP with g ood precision and adequate accuracy. The effects of HPLC mobile-phase compo nents on the ionization efficiency and sensitivity of detection in the posi tive ionization mode, the evaluation of the matrix effect, and limitations in sensitivity of detection of I due to the formation of multiply charged s pecies are presented. (C) 1999 Elsevier Science B.V. All rights reserved.