Rapid determination of creatinine in serum and urine by ion-pair high-performance liquid chromatography

We report a simple and reliable high performance liquid chromatography meth od for measuring creatinine in serum and urine. The chromatographic run is performed on a C-18 column after protein precipitation with acetone and add ition of cimetidine as an internal standard. The separation is carried out in 20 min at a flow rate of 0.8 ml/min, with a mobile phase consisting of 1 00 mmol/l sodium dihydrogen phosphate solution, containing 30 mmol/l sodium lauryl sulfate pH 3.0 and acetonitrile (60:36, v/v). The absorbance is mon itored at 200 nm. The relationship between creatinine concentration and the creatinine/internal standard peak area is linear up to 1,088 mu mol/l. Wit hin-run precision measured at three different creatinine concentrations ran ges from 0.89% to 2.34% in serum and from 0.34% to 1.10% in urine. Between- run precision varies from 1.68% to 3.17% in serum and from 1.58% to 1.85% i n urine over a wide range of concentrations. Analytical recovery is between 98.71% and 101.25% in serum and between 98.96% and 100.27% in urine. The d etection limit is 3.24 mu mol/l for a signal-to-noise ratio of 3. The metho d shows a good linearity with the reference isotope dilution gas chromatogr aphy-mass spectrometry procedure (r=0.999), without interferences, even in the presence of high bilirubin concentrations.