SOFT 2004 Meeting Abstracts - Society of Forensic Toxicologists

A79
LC-MSIMS METHOD DEVELOPMENT FOR A PACLITAXEL ASSAY
W. Lambert"' I, K. Mortier!, A. Verstraete 2 , and C. Van Peteghem 1 , I Laboratorium voor Toxicoiogie, Ghent
University, Hareibekestraat 72, B-9000 Gent, Belgium, 2Afdeling Klinische Bioiogie, Ghent University
Hospital, De Pintelaan 185, B-9000 Gent, Belgium
The development of a method with liquid chromatography coupled to mass spectrometry (LC-MS) for the
determination of the anticancer drug paclitaxel in plasma is described. The goal of the method is to produce
accurate and reproducible data, in a sensitive assay. Therefore, factors that influence reproducibility are
investigated. The method consisted of a basic Iiquidlliquid extraction of plasma with methyl-t-butyl ether.
Subsequently, samples were analyzed using a standard narrow bore reversed phase column. MRM
transitions of pac lit axel and the internal standard (cephalomannine) were monitored. Special attention was
given to two typical electrospray phenomena: adduct formation and matrix effect. First of all, adduct
formation was investigated. In the absence ofadditives like formic acid or ammonium acetate in the mobile
phase, reproducibility of the LC-MS method was decreased, when samples of varying alkali metatcontent
were analyzed. Already at a low concentration of additive in the mobile phase reproducibility increased to
an acceptable level. Therefore, a small amount of additive was incorporated in the mobile phase. Different
mobile phase additives were tested for optimum sensitivity and reproducibility. Secondly, matrix effect was
examined, especially the influence of the vehicle used in the commercial formulation of paclitaxel (Taxo\):
Cremophor EL. Ion suppression by formulation vehicles has been reported for e.g. polyethyleneglycol400.
In view of the application of this method in a pharmacokinetic study with Taxol, investigation of the effect
ofCremophor EL on the ionization was incorporated in the method development. When an isocratic LC run
was used, ion suppression was noticed mainly as a result of carry-over to subsequent runs. Changing the
mobile phase to a higher percentage of organic phase and incorporating a gradient step (column wash)
resolved the matter. The strategy to evaluate and eliminate adduct formation as well as matrix effects can
also be applied to LC-MS determinations of other compounds and in fact should become an essential part
ofa validation protocol.
Keywords: Paclitaxel, Method development, LC-MS
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