“…The preparation of saliva samples for metabolomics analysis is quite simple. In general, the procedures involve protein precipitation with acetonitrile [ 189 , 190 , 191 , 192 , 193 , 194 , 195 ], methanol [ 196 , 197 , 198 ], or a combination of methanol/acetonitrile (1:1, v / v ) [ 199 , 200 , 201 ], methanol/water [ 202 , 203 , 204 , 205 , 206 ], and methanol/acetonitrile/water (2:2:1, v / v / v ) [ 207 ]. Other studies have used isopropanol [ 208 ] or acetone [ 209 ], which requires evaporation and resuspension in an appropriate solvent before chromatographic analysis.…”