Determination of plasma bile acids by capillary gas-liquid chromatography-electron capture negative chemical ionization mass fragmentography.

Combined capillary gas-liquid chromatography-electron capture negative chemical ionization mass spectrometry of pentafluorobenzyl ester-TMSi ether derivatives of bile acids and isotope dilution using deuterated internal standards are introduced as a sensitive and selective analysis technique for plasma bile acids. As a result of the high ionization efficiency of pentafluorobenzyl derivatives under electron capturing conditions and minimal fragmentation, the detection limit of this technique is low: 1 pg for each bile acid. The high sensitivity enabled the detection and quantitation of atypical bile acids in 200-microliters aliquots of plasma from fasting healthy adults as exemplified by trihydroxycoprostanic acid (0.002 +/- 0.001 mumol/l) and dihydroxycoprostanic acid (0.013 +/- 0.002 mumol/l).