Simultaneous quantitative analysis of methyl salicylate, ethyl salicylate and salicylic acid from biological fluids using gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric (GC-MS) assay was developed for the quantitative analysis of methyl salicylate (MeS), ethyl salicylate (ES) and salicylic acid (SA) from biological fluids. The method was validated from 100-microl rat liver homogenate preparations (5 mg/ml protein) in 70 mM KH2PO4 (pH 7.4) buffer and from 100 microl rat plasma. The samples were extracted with chloroform, derivatized with BSTFA and quantitated by GC-MS in the SIM mode. The standard curves ranged from 31 ng/ml to 800 or 1250 ng/ml. Relative standard deviations and bias were less than 11% in plasma and homogenate for all compounds except SA which evidenced greater variability. The assay was used in preliminary experiments to characterize the pharmacokinetics of MeS in rats.