Quantification of glutaric acid by isotope dilution mass spectrometry for patients with glutaric acidemia type I: selected ion monitoring vs. selected ion storage

Abstract

An isotope dilution mass spectrometric assay for the quantification of glutaric acid in urine and serum samples was developed. The performance of a quadrupole mass filter (QMF) gas chromatography–mass spectrometry (GC–MS) instrument, operated in the selected ion monitoring mode, and a quadrupole ion trap (QIT) GC/MS instrument, operated in the selected ion storage mode, was compared. Both instruments gave linear standard curves with glutaric acid concentrations between 0.19 and 3.8 μM. The average coefficients of correlation were 0.9998 and 0.9993 for the QMF and the QIT system, respectively. There was good agreement between the glutaric acid concentrations measured with the two instruments. The run-to-run precision was between 1.2 and 3.7% and between 6.2 and 8.6%, the average recovery of glutaric acid in urine and serum samples was 96 and 103% with the QMF and QIT instrument, respectively. We conclude that although the QMF has a slightly better performance, both instruments can be used to reliably measure glutaric acid concentrations from urine and serum patient samples.