Mass spectrometric quantification of cysteine‐containing leukotrienes in rat bile using 13 C‐labeled internal standards

Leukotriene C 4 and N ‐acetyl leukotriene E 4 were determined in rat bile using a procedure based on high‐performance liquid chromatographic fractionation, hydrogenation to 5‐hydroxyeicosanoic acid, and gas chomatographic/mass spectrometric selected ion monitoring analysis of the pentafluorobenzyl ester, trimethylsilyl ether derivatives. 13 C 4 ‐Labeled analogs of the leukotrienes were synthesized and used as internal standards. The concentrations of both leukotrienes in rat bile were markedly elevated after administration of endotoxin to anesthetized animals; N ‐acetyl leukotriene E 4 was the more abundant product. The presence of leukotriene C 4 in rat bile after endotoxin challenge was confirmed by fast atom bombardment/tandem mass spectrometry with precursor ion scanning. Quantitative determination of leukotriene C 4 using the tandem mass spectrometric procedure was consistent wth the gas chromatographic/mass spectrometric data but the latter procedure gave a substantially lower detection limit.