Conditions for solid-phase extraction of urinary bile acids with octadecylsilane-bonded silica

Fast atom bombardment mass spectrometry was used as a detection method in a study of the extraction of urinary bile acids with octadecylsilane-bonded silica. The procedure commonly used in many laboratories was found to result in significant losses of sulfated taurine-conjugated bile acids. Losses of other double conjugates and of bile acid and bile alcohol glucuronides were also seen. The losses were avoided by addition of an equal volume of 0.5 M triethylamine sulfate to the urine before passing it through the sorbent bed. Quantitative elution was then achieved with methanol. Batch variations were observed with sorbents from two different manufacturers.