Gas chromatography of bile acids

Bile acids, the end products of cholesterol metabolism in the liver, are of vital importance in the tissue distribution of cholesterol. Abnormalities in cholesterol biosynthesis or metabolism are often reflected in the proportions, concentrations and conjugation of bile acids in various tissues and determination of bile acids in these tissues is important in the diagnosis of hepatobiliary diseases. Several methods for quantitative determination of bile acids in biological fluids are known and have been reviewed. In this review, we have discussed the gas-chromatographic method for determination of bile acids with special reference to bile acid quantitation in plasma, bile, urine and stool.

High-performance liquid chromatographic-electrospray mass spectrometric analysis of bile acids in biological fluids

The present work describes the development of HPLC-mass spectrometric systems equipped with an electrospray interface for the quantitative analysis of bile acids. Good separation of free as well as glycine- and taurine-conjugated bile acids was achieved with a C18 reversed-phase column (3 microns particle size, 70 x 4.6 mm I.D.) employing methanol-15 mM ammonium acetate as the mobile phase for both isocratic and gradient mode, at a flow-rate of 0.3 ml/min. This system permits post-column splitting of the eluate for analysis by two different detectors: (1) electrospray-mass spectrometer with a flow-rate of 18 microliters/min; and (2) a complementary evaporative light scattering mass detector. When bile salts were ionized in the electrospray interface operating in the negative-ion mode, only [M-H]- molecular ions were generated; the detection limit was 15 pg injected for all bile acids studied. In the second system, a semi-micro pre-column splitting apparatus (Acurate, LC Packings) was utilized: with this device the flow-rate from the HPLC pump was reduced to 1.4 microliters/min and bile acids were separated with a micro-bore C18 column (3 microns particle size, 150 x 0.30 I.D.), using the same mobile phase as above. With this latter system, a head-column enrichment technique can be used: the amount injected can be increased from 60 to 200 nl, permitting an improvement in the detection limit to 5 pg injected. Application of the HPLC-electrospray-mass spectrometric method to bile and serum bile acid analysis is described; preliminary data on the ability of the first system to determine the 13C/12C isotope ratio in 13C-labeled bile acid enriched serum is also critically discussed.