Gas-chromatographic determination of urinary oxalate

We describe a simple, rapid method for determining urinary oxalate: isolation by precipitation with calcium chloride and conversion to dimethyl oxalate, which then is measured by gas chromatography. To each sample, tracer amounts of 14C-labeled oxalic acid are added, to determine the analytical recovery of urinary oxalate. Analytical recovery of [14C]oxalic acid added to urine specimens ranged from 15 to 95% (mean, 80%), and corrected recovery, based on calculation isotope-dilution techniques, ranged from 98 to 100%. The urinary excretion of oxalic acid by 18 normal men, ages 23 to 43 years, ranged between 9 and 23 mg/24h, with a mean value of 16 mg; that by 68 patients with small-bowel bypass ranged from 60 to 210 mg/24 h, with a mean of 127 mg.