Metabolite profiling of hemodialysate using gas chromatography time-of-flight mass spectrometry

Hemodialysis is an important alternative for renal replacement therapy to remove uremic retention solutes (URS) for the uremic syndrome. The metabolites in the hemodialysate directly reflect the efficiency of URS clearance. Here we report a highly sensitive and reliable metabolomic procedure for the measurement of small molecule metabolites in hemodialysate using gas chromatography coupled with time-of-flight mass spectrometry (GC/TOF/MS). The method was developed and evaluated through orthogonal experimental design using multivariate statistical analysis. The optimized method involves the use of methanol and water in the ratio of 3:1 (v/v) for dissolving the lyophilized solid of the hemodialysate after degradation of urea with urease (no less than 50 U) for 10 min. Validation of the method demonstrated a good linearity with regression coefficients greater than 0.99. Relative standard deviations of precision and stability of proposed method were less than 15%, and recoveries ranged from 71.8 to 115.8%. This method was successfully applied in the metabolite profiling of human hemodialysate samples which was able to differentiate the patients treated with high-flux hemodialysis from those with low-flux hemodialysis. The metabolomic results reveal a higher concentration of URS, and thus, better URS removal, from the patients under high-flux dialysis than those under low-flux dialysis.