Quantification of bile acids directly from urine by MALDI-TOF-MS

The ability to quantify mixtures of bile acids using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry directly from urine has been demonstrated. Six cholic acid derivatives were selected for analysis: taurocholic acid (TCA), taurochenodeoxycholic acid (TCDCA), taurolithocholic acid (TLCA), glycocholic acid (GCA), glycochenodeoxycholic acid (GCDCA), and glycolithocholic acid (GCDCA). Urine samples were pre-concentrated and purified using solid-phase extraction (SPE) columns. The method was optimized to eliminate suppression effects, and proved to be reproducible from day to day. Calibration curves averaged from three days were obtained for the bile acids directly from urine, and then tested for their ability to accurately determine concentrations from one measurement. In summary, a simple, rapid method has been developed for the quantification of bile salts from urine with SPE clean-up by MALDI-MS.