Rapid and direct determination of creatinine in urine using capillary zone electrophoresis

Background: In clinical medicine creatinine determination is used for the diagnosis of renal diseases and muscular dysfunctions. Also, in forensic toxicology creatinine concentration is used as a standardization tool for the quantitative measurement of therapeutic or illicit drugs and xenobiotics in urine. The present work was aimed at developing a robust and reliable CE determination of creatinine in urine, meeting the needs of simplicity, rapidity and low cost required by routine toxicological screening. Methods: The optimized buffer electrolyte was composed of 200 mM phosphate and 200 mM acetic acid (pH 3.8). The separation capillary (50 μm × 10 cm of effective length) was made of naked fused silica. Separations were carried out under 25 kV potential. Urine samples were diluted 20 fold with water and directly injected. Direct UV absorption detection at 200 nm was employed. Results: Linearity was assessed in the range 0.2-32 mM. Precision tests resulted in CV's % below 0.56% for migration times and below 3.78% for peak area ratios (analyte/I.S.). Conclusions: The described CE creatinine assay meets the strict requirements of forensic analysis and looks particularly useful to test the possible adulteration or dilution of urine samples undergoing toxicological screening.