Galactonate determination in urine by stable isotope dilution gas chromatography–mass spectrometry

Abstract A stable isotope dilution assay was developed for the sensitive determination of d -galactonic acid. d -[U- 13 C 6 ]galactono-1,4-lactone was prepared as internal standard. Unlabelled and U- 13 C -labelled d -galactonic acid species were converted to the N -(1-butyl)galactonamide pentaacetate derivatives and assessed by gas chromatography–mass spectrometry (GC–MS). Positive chemical ionisation and monitoring of the [ M H-60] + -ions in the galactonate chromatographic peak at m / z 402 and m / z 408 were used for quantification. The procedure was applied to study the variability of d -galactonate excretion in healthy subjects and galactosemic patients and to monitor the d -galactonate– d -galactitol ratio in human urine.