Determination of urinary oxalate by ion chromatography: some modifications

Abstract

イオンクロマトグラフィーを尿中蓚酸測定に応用した.標準曲線は蓚酸0.5～10 μg/mlの範囲で有意の直線関係を示した.測定限界は0.02 μg/mlであった.尿中蓚酸測定をおこなった結果, 再現性を良好にするには2つの問題点を発見した.尿は常に蓚酸カルシウムの過飽和溶液であることと, クロマトグラム上で隣のピークである硫酸が干渉することであった.その証拠に尿を稀釈し蓚酸のピークを測定し求めた値を比較すると10倍稀釈の蓚酸値がもっとも低く, 稀釈倍数とともに値は増加し, 100倍稀釈の値が最高であった.一定量の蓚酸1 μg/mlを含む溶液中に共存する硫酸濃度が増加すると, その蓚酸の回収率は低下する.再現性を良好にするには各尿サンプルの100倍稀釈と, それに蓚酸0.25 μg/mlを添加したものを測定し, これらにより値を求めることが必要である

Ion chromatography was used to determine urinary oxalate concentration. The minimal detectable limit in a standard solution was 0.02 microgram/ml, and the regression line for the standard curve from 0.5 to 10 micrograms/ml had a significant correlation coefficient (p less than 0.01), but it was difficult to obtain reproducible results with ion chromatography. There were two obstacles: Urine was always oversaturated with calcium oxalate, and the presence of sulfate, the peak of which is next to the oxalate peak on the chromatogram of urine, seemed to interfere with oxalate conductivity. Comparison of 4 different dilutions of urine showed that the oxalate conductivity was highest in the 100-fold dilution and decreased gradually with increasing concentration. The conductivity of the oxalate standard (1 microgram/ml) also decreased as the concentration of sulfate increased. Therefore, it was concluded that to obtain reproducible results urine should be diluted 100-fold and that a recovery test by adding 0.25 microgram/ml oxalic acid should be performed on all urine samples.