Rapid screening for acidic non-steroidal anti-inflammatory drugs in urine by gas chromatography mass spectrometry in the selected-ion monitoring mode

A rapid screening procedure is described for the simultaneous determination of various acidic non-steroidal antiinflammatory drugs (NSAIDs) at sub-nanogram levels. The procedure involves solid-phase extraction (SPE) of NSAIDs using Chromosorb P as the adsorbent in partition mode, with subsequent single-step conversion to tert.-butyldimethylsilyl (TBDMS) derivatives, followed by direct analysis by gas chromatography-mass spectrometry (GC-MS). The characteristic [M-57](+) high-mass ions constituting the base peaks in the electron-impact mass spectra of most TBDMS derivatives permitted sensitive detection of NSAIDs by GC-MS in selected-ion monitoring (SIM) mode, even in the presence of higher levels of coextracted urinary organic acids. The detection limit for SIM of each drug was in the range 0.03-0.9 pg. When applied to urine samples (250 mu l) spiked with NSAIDs, the present GC-SIM-MS method allowed simultaneous screening for various NSAIDs with good overall precision and accuracy in the range of 10-40 ng.