Determination of Urinary Oxalate by Ion Chromatography

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Abstract
The factors which are important for calcium oxalate renal stone formation may be studie, in vitro, using the constant composition mineralization method (Gaur and Nancollas, Kidney Int., 26, 767 (1984). Since the molar calcium/oxalate rations in vivo are relatively high (normal range, 5–50) the rates of these seeded crystallization reactions at constant supersaturations are markedly dependent upon the concentrations of oxalate ion. Kinetic studies therefore require a rapid and reliable method for the analysis of this ion. A Dionex QIC analyzer incorporating an anion fiber suppressor unit and conductometric detector has been used to develop a method for the determination of urinary oxalate. The eluent, consisting of a mixture of 3.23 × 10−3 mol L−1 NaHCO3 and 2.41 × 10−3 mol L1 Na2CO3, was used isocratically at a flow rate of 2.2 cm3 min−1. The 14 min analysis time was considerably shorter than that reported for previous ionchromatographic methods. The minimum detectactable oxalate in urine was 0.11 × 10−3 mol L−1 with a RSD of about 10%. The method is especially suitable for monitoring oxalate in urine mineralization experiments.