An on-line solid phase extraction procedure for the routine quantification of urinary methylmalonic acid by liquid chromatography-tandem mass spectrometry

Background: The goal of this study was to develop and to validate
an improved isotope-dilution-liquid chromatography-tandem mass
spectrometry (LC-MS/MS) method for the quantification of
methylmalonic acid (MMA) in urine. Methods: A previously described
sample preparation protocol requires two solvent extraction steps,
including evaporation. The first extraction is to extract the
analyte from the sample, and second occurs following derivatization
of the extract. In the method described here, the second
evaporation step was substituted by on-line solid phase extraction
employing column-switching and a permanent co-polymer based
extraction cartridge. A standard validation protocol was applied to
investigate the performance of the method. Results: The method was
found to be linear in the clinically relevant range of
concentrations (6-100 mu mol/L). Total coefficients of variation
were below 10% and inaccuracy was