Screening techniques for the detection of inborn errors of bile acid metabolism by direct injection and micro-high performance liquid chromatography–continuous flow/fast atom bombardment mass spectrometry

Two methods, direct injection–continuous flow fast atom bombardment (DI–CF/FAB) mass spectrometry and micro-high-performance liquid chromatography (μHPLC)–CF/(FAB) mass spectrometry were developed for the clinical analysis of urinary bile acids and their conjugates, specifically for the diagnosis of disorders of bile acid metabolism. The method based upon DI of urine extracts into the CF/FAB flow stream was developed for the rapid screening of large numbers of patient samples. It allows injections to be made at 4 min intervals for high sample throughput. Analyses of standard mixtures of bile salts demonstrate that linear response curves are obtained over more than a hundred-fold concentration range with a minimum detectable amount in the picogram range. Oxo bile salts are identified by reduction with sodium borodeuteride followed by reanalysis for detection of any reduction products. This methodology has been used for the analysis of over 1000 specimens. A reverse-phase μHPLC–CF/FAB mass spectrometric method was also developed for use in the confirmation or further investigation of screening results. With no additional sample preparation this method permits the separation, identification and quantitation of urinary bile salt isomers within a 45 min analysis time.