Significant higher levels of allantoin in both plasma and erythrocytes of patients with chronic renal failure indicate that allantoin may be used as a good marker of oxidative stress.
A method for the measurement of ascorbic acid using HPLC with UV detection and investigation into the protein precipitation techniques with regard to stability and recovery are described. The effectiveness of various protein precipitants was tested. Stability of ascorbic acid samples for analysis was investigated over 10 h. Ascorbic acid samples extracted with metaphosphoric acid were stable on a cooled autosampler (4 degrees C) for at least 10 h (with a decline of 1.8% for ascorbic acid solution and 2.8% for plasma). Perchloric acid as protein precipitant for ascorbic acid was unsuitable (with a decline of 36.0% for ascorbic acid solution and 7.3% for plasma). Analytical performance of this method is satisfactory. The intra- and interassay coefficients of variation were 2.1% (n = 10) and 5.8% (n = 12), respectively. The calibration curve was linear with the tested range of 2.0-250.0 micromol/L. The recovery was 96.1% with CV = 4.8% (n = 6) and the LOD was 3 micromol/L. The preliminary reference ranges of ascorbic acid in a group of blood donors are 50.8 +/- 22.4 micromol/L. This assay is a highly sensitive and reproducible HPLC method for the determination of ascorbic acid in human plasma.
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