Plasma creatinine and creatine quantification by capillary electrophoresis diode array detector

Traditional clinical assays for nonprotein nitrogen compounds, such as creatine and creatinine, have focused on the use of enzymes or chemical reactions that allow measurement of each analyte separately. Most of these assays are mainly directed to urine quantiWcation, so that their applicability on plasma samples is frequently hard to perform. This work describes a simple free zone capillary electrophoresis method for the simultaneous measurement of creatinine and creatine in human plasma. The eVect of analytical parameters such as concentration and pH of Tris–phosphate running buVer and cartridge temperature on resolution, migration times, peak areas, and eYciency was investigated. Good separation was achieved using a 60.2-cm£75-m uncoated silica capillary, 75mmol/L Tris–phosphate buVer, pH 2.25, at 15 °C, in less than 8min. We compared the present method to a validated capillary electrophoresis assay, by measuring plasma creatinine in 120 normal subjects. The obtained data were compared by the Passing– Bablok regression and the Bland–Altman test. Moreover the performance of the developed method was assessed by measuring creatine and creatinine in 16 volunteers prior to and after a moderate physical exercise.  2005 Elsevier Inc. All rights reserved.