Simultaneous determination of creatinine and uric acid in urine by liquid chromatography–tandem mass spectrometry with polarity switching electrospray ionization

A simple liquid chromatography–tandem mass spectrometric (LC–MS/MS) method was developed and validated to simultaneously determine creatinine (Cr) and uric acid (UA) levels as a confirmatory method for adulteration or dilution of urine. Centrifuged urine samples (10 μL) were diluted with 390 μL of distilled water. 30 μL of internal standard solution (Cr-d3, 5 μg/mL) and 10 μL of acetonitrile were added to 20 μL aliquots of diluted urine samples and filtered. The samples (1 μL) were introduced into LC–MS/MS with no further pretreatment. Cr and UA were separated on a multi-mode ODS column (Scherzo SM-C18, 75 mm × 2.0 mm I.D., 3 μm) and quantified by LC–MS/MS with polarity-switching electrospray ionization. Cr requires the positive-ion mode, whereas the negative-ion mode is required for the analysis of UA. The linear ranges were 1.0–300 mg/dL for Cr and 0.5–300 mg/dL for UA, with good determination coefficients (R2 ≥ 0.9988). The intra-day and inter-day precision of the analytes was within 13.0% and 14.4%, respectively. The intra-day and inter-day accuracy was −8.8 to 3.7% and −0.3 to 6.6%, respectively. The lower limits of detection (LLODs) were 0.3 mg/dL for Cr and 0.07 mg/dL for UA. The applicability of the developed method was examined by analyzing urine samples from suspected drug abusers (n = 46).