High-performance capillary zone electrophoretic assay for markers of diabetic nephropathy in plasma and urine

A new high-performance capillary zone electrophoretic assay for creatine (Cr), creatinine (Cn), urea (U) and uric acid (Ua), markers of human diabetic nephropathy, both in plasma and urine has been developed with UV detection at 200 nm. The plasma sample was deproteinized with trichloroacetic acid and centrifuged at 10 000 rpm for 10 min. The urine sample was diluted 20-fold with buffer before analysis. The optimum separation conditions for the markers was investigated with respect to the concentration of the buffer, the pH, the voltage and the capillary temperature. Baseline separation was achieved in 25 mmol/L phosphate buffer (pH 3.45) using a 21 cm×75 μm I.D. fused-silica capillary at 40 °C with an electric field of 1190 V/cm. The calibration curves showed good linearity in the range 3.5–1000, 0.18–700, 500–5000 and 2–800 μM (r2min>0.998) for Cr, Cn, U and Ua, respectively. The proposed method also has a high reproducibility (peak area RSDmax<3%) and has been successfully applied to the determination of clinical samples.