Abstract
DURING the course of a series of metabolic experiments in which 1-13C-ascorbic acid and 1-13C-glycine were fed to a normal adult1 and hyperoxaluric patients2 daily samples of urinary oxalic acid were isolated as calcium oxalate for estimation of the 13C enrichment. It was found expedient to determine the daily levels of excretion by the method of isotope dilution, using the specific 14C-activity of the oxalate samples prior to combustion to CO2 for mass spectrometric analysis. The amounts of 14C and 12C added were low and hence did not interfere with the measurement of 13CO2. Previously reported methods for calcium oxalate estimation have the disadvantage that they depend on the complete recovery of oxalate from a sample of the urine3–7. Using the method of isotope dilution, however, the only exacting requirement is the purity of the final product, which is checked by repeated reprecipitation to constant specific activity.
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