Enhanced method performance due to a shorter chromatographic run-time in a liquid chromatography?tandem mass spectrometry assay for paclitaxel

Abstract

Liquid chromatography–tandem mass spectrometry (LC–MS–MS) is often performed in a high-throughput environment. Unfortunately, with atmospheric pressure ionization (API) techniques, shorter run-times or reduced sample clean-up often result in ion or matrix suppression, which can lead to erroneous results. The present work on the analysis of paclitaxel compares ion suppression, sensitivity and linearity of a high-throughput LC–MS–MS method (0.8 min run-time, method B) to a method with increased separation (2.0 min run-time, method A). An atmospheric pressure chemical ionization (APCI) interface was used for both methods. The high-sample-throughput method uses an increased amount of organic solvent in the mobile phase (isocratic, 85% versus 70% of methanol) and a higher flow-rate (600 μl/min versus 400 μl/min). As a result, internal standard (docetaxel) and target analyte (paclitaxel) co-elute, close to, although separated from the solvent front. Ion suppression of both methods was evaluated by comparing pure standard to plasma and plasma containing a vehicle. Sensitivity and linearity were compared by injecting matrix matched calibration samples with both methods. Ion suppression by the vehicle Cremophor EL led to poor data quality for the standard method (A), while for the short method (B), ion suppression was compensated for by the co-eluting internal standard. The short method showed similar linearity but increased sensitivity by at least a factor five. This work provides a strategy to compensate for ion suppression without the use of labeled internal standards. In addition, a better sensitivity and a shorter run-time are noted.