Figure 5.

Number of peaks detected in the NMR spectra of urine after extraction into ethyl acetate solvent at different pH. The number is maximum at lower pH and is generally reduced as the pH is increased. Protonation of carboxylic acid groups increases with decreasing pH and hence the number of carboxylic acids class of metabolites extracted into the ethyl acetate solvent increases at lower pH. Note, the number of metabolite peaks was determined based on a minimum intensity threshold (MI) and peak picking sensitivity (PC) of 0.1. The numbers, however, become far higher when a lower threshold is selected.