Semi-automated quantification of methylmalonic acid in human serum by LC-MS/MS

Abstract

Background. Methylmalonic acid (MMA), a sensitive biomarker of functional vitamin B12 deficiency, is commonly determined by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography–tandem mass spectrometry (LC-MS/MS) methods using manual extraction and derivatization of MMA to reduce polarity prior to separation. Methods. In the present study we introduce a semi-automated extraction on a strong anion exchanger, HPLC separation on a BEH-amide column to separate serum MMA from its abundant isoform, succinic acid, followed by MS/MS detection and quantification. Results. The extraction of MMA plus internal standard provides full recovery and the method is linear between 0.03 μmol/L and 20.0 μmol/L (r² = 1.0) with intra-and inter-assay imprecision of 2.2%. Agreement with other laboratories has been demonstrated in external proficiency testing. Compared to both conventional GC-MS and LC-MS/MS methods, the correlation is r² > 0.99. Conclusions. The use of robotic pipetting, elimination of derivatization and improved separation by the BEH-amide column combined with HILIC chromatographic conditions significantly improve sample throughput compared to conventional methods. Using a single pipetting robot and LC-MS/MS instrument, this method is currently performing 180 analyses per day from10 regional hospitals and several additional distant sites.

Key Words::

• Chromatography
• high performance liquid
• tandem mass spectrometry
• gas chromatography-mass spectrometry
• methylmalonic acid
• vitamin B12

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.