Ion chromatographic determination of oxalate in plasma: correlation study with an enzymatic method

An ion chromatographic (IC) method for the determination of oxalate in plasma was developed. The method exploits a rapid and simple sample preparation step that substantially reduces the plasma chloride level to facilitate the oxalate determination. The chloride is removed as silver chloride by using a cation-exchange resin in the silver cation form. The dependence on chloride concentration and pH was evaluated. The oxalate recovery in plasma samples was found to be 93 ± 18% (n=4 trials) according to a standard addition study. A comparison of the IC method with an enzymatic method indicated that both methods measure the same oxalate concentration over the range examined, 5–300 μM. Furthermore, the comparison involved a correlation study that allowed cross-validation of the two methods, suggesting that neither is adversely affected by interferences. The detection limit of the IC method was 0.5 μM or 4.4 ng oxalate.