SIMPLE, RELIABLE CHROMATOGRAPHIC MEASUREMENT OF OXALATE IN URINE

In this assay for oxalate in urine,oxalateis adsorbed from the urine onto graphitized carbon black (Carbopack B). After desorption and removal of the solvent, oxalic acid is gas-chromatographically measured after being derivatized with BF3/methanol. Chromatography is on Carbopack B/polyethylene glycol (M. 20 000), 93.7/6.3 by weight. The lower limit of detection of urinary oxalate is about 3 mg/L (CV _ 3.6%). A series of oxalate determinations in 24-h urine samples of 15 subjects gave a mean of 47.1 (SD 15.4) mg/24 h, with an analytical recovery of 97.4% (SD 3.0%, range 93.6-102.4%). Total analysis time for one sample is about 2 h