Bile acid concentrations in serum are measured by liquid chromatography-tandem mass spectrometry stable isotope dilution analysis. Serum is mixed with isotopically labeled internal standards of selected bile acids and then subjected to protein precipitation. Sample preparation is semiautomated using a liquid handler. Reverse phase liquid chromatography is performed using mobile phases composed of water:methanol (95:5; 10 mmol/L ammonium acetate) and methanol (10 mmol/L ammonium acetate) to separate free bile acids, their respective tauro- and glyco- conjugates and 2 bile acid precursors.(Unpublished Mayo method)
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