Creatinine measurements in 24 h urine by liquid chromatography-tandem mass spectrometry

A simple, sensitive, and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determining urinary creatinine was developed and used to evaluate 24 h urine samples collected during an exposure study. Urine (1 μL) was diluted with methanol and then directly applied to LC-MS/MS. Under electrospray ionization (ESI) conditions, the transition molecules of creatinine and creatinine-d₃ were observed at m/z 114 > 44 and m/z 117 > 47, respectively. The retention time of creatinine was 0.59 min. The linear range was 1-2000 ng/mL, with a detection limit in urine of 1 ng/mL. LC-MS/MS and colorimetric end-point methods were significantly associated (R² = 0.8785, p < 0.0001). The LC-MS/MS method to determine creatinine in 24 h urine samples had shorter retention times, was more sensitive, reliable, reproducible, simple, selective, and used a smaller sample size than other LC-MS/MS or commercial methods.