Detergent and ion-pair extraction of bile acids in liver tissue for analysis by fast atom bombardment mass spectrometry.

Methods for detergent and ion-pair extraction and group separation of bile salts in liver tissue using decyltrimethylammonium bromide (DTMAB), Lipidex 1000 and octadecyl-bonded silica were studied. Samples of rat liver were homogenized in 0.1 M DTMAB and the supernatants were diluted to 0.03 M DTMAB and passed through a column of Lipidex 1000/Sep-Pak C18. After washing with water, the bile salts were eluted with 70% aqueous methanol. The recovery of endogenous bile acids labelled with 14C in vivo was quantitative. Part of the extracted lipids and remaining DTMAB was removed by a second extraction on Sep-Pak C18, resulting in 84% recovery of bile acids in an extract suitable for analysis by fast atom bombardment mass spectrometry. The amount of extract required for this analysis corresponded to 5-10 mg of rat liver tissue. The ion-pairs of unconjugated and conjugated mono-, di- and trihydroxy bile acids could be separated into groups by reversed-phase chromatography on mu Bondapak C18 prior to mass spectrometric analysis.