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

Abstract

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.