Selection of the appropriate elution conditions was made attending to the recovery of the analytes,the volume needed for an acceptable recovery, and the compatibility with the analytical method [17,18].Despite the fact that the use of acidic, basic buffers or solutions with high ionic strength has been reported, organic solvent/water mixtures such as MeOH/water, acetonitrile/water, ethanol/water have often achieved the best recovery for small molecules. As shown in Table 1, the best recovery (>80%) with less matrix interferences was obtained with methanol and ethanol.