Effect of pH on 1H-NMR spectroscopy of mouse urine.

1H-NMR spectroscopy of urine has been proved to be a powerful tool in metabonomic investigations in the field of chemical toxicity evaluation and disease diagnosis. However, most studies on urinary metabolite profiling by 1H-NMR have been conducted using rat urine. In the course of experiment on 1H-NMR analysis of urine samples of mice administered selenium compound, we noticed a substantial variation of chemical shift of citrate among individual mice. To clarify the effect of urinary pH on chemical shift of citrate, we compared 1H-NMR spectra of urine samples obtained from selenium-treated mice and untreated mice as well as those from untreated rats. The results clearly showed a linear relationship between urinary pH and chemical shift of citrate in 1H-NMR spectra both in mice and rats. The urine of mice exhibited a wider variation of pH, resulting in a wider variation of chemical shift of citrate than that of rats. We also recognized a clear peak of trimethylamine in urine of mice, but not that of rats. These data indicate that more attention should be paid to the characteristics of mouse urine with special reference to pH and trimethylamine metabolism in the analysis of NMR spectroscopy.