LC-MS-MS measurements of urinary creatinine and the application of creatinine normalization technique on cotinine in smokers' 24 hour urine

A simple and sensitive high performance liquid chromatography-tandem mass spectrometry (hplc-esi-ms-ms) method was developed and validated for the quantification of creatinine in human urine. the analysis was carried out on an agilent zorbax eclipse xdb-c18 column (2.1×150 mm,3.5 m). the mobile phase was 0.1% formic acid in water and 0.1% formic acid in acetonitrile (50/50,v/v). linear calibration curves were obtained in the concentration range of 1-2000.0 ng/ml,with a lower limit of quantification of 0.99 ng/ml. the intra- and interday precision (rsd) values were below 3%. the method was successfully applied to a bioequivalence study of creatinine in chinese smokers and nonsmokers. the total cotinine in 24 h urine and cotinine: creatinine ratio were also positively associated (pearson r=0.942,p<0.0001). however,cotinine: creatinine ratio varied significantly across smoking groups for the difference of individual. 24 h urinary cotinine was more appropriate for expressing correlation with tar than cotinine: creatinine ratio. © 2012 hongwei hou et al.