Capillary electrophoretic determination of oxalate in amniotic fluid Original Research Article

A capillary electrophoretic (CE) assay for oxalate has been applied to the quantitative determination of free oxalate in amniotic fluid. Indirect absorbance detection of oxalate is accomplished with a chromate-based background electrolyte modified with ethylenediaminetetraacetic acid (EDTA). Detection interference due to the presence of high levels (≈4 mg/ml) of inorganic chloride is eliminated through a direct sample clean-up procedure based on cation (Ag+-form) resins. Separation interference from amniotic fluid proteins is prevented through the use of a simple aqueous-based dilution procedure. This method for the determination of oxalate in amniotic fluid provides precision of ≈5% relative standard deviation (RSD). Within-day precisions for the oxalate response and migration time are better than 3% RSD and 1% RSD, respectively. Between-day precisions for the oxalate response and migration time are better than 6% RSD and 3% RSD, respectively. The analytical recovery of oxalate (1000 ng/ml) spiked into amniotic fluid was better than 96%. The limit of detection (LOD) for the method is ≈100 ng/ml oxalate. This method also shows promising results for the determination of oxalate in human blood plasma samples.