Rapid method for the determination of urinary oxalic acid by gas liquid chromatography (author's transl)

A rapid method for the determination of urinary oxalic acid by gas-liquid chromatography is described. The procedure involves extraction of oxalate from urine by tetrahydrofuran followed by evaporation to dryness and subsequent with diesterification with the boron-trifluoride propanol. The derivative is extracted with hexane and is detected by FID gas chromatography. Malonic acid is used as internal standard. Analytical recovery ranged from 94 to 105%. The coefficient of variation in replicate aliquots over the entire range is less than 6%. The expected range for our method is calculated to be 44 to 577 mumol of oxalate per 24-h urine.