The washing steps were optimised in order to obtain the best sample clean-up. In particular, the last step (washing with water/MeOH,80/20) was the best compromise between satisfactory sample purification (which improved as expected when increasing the percentage of MeOH) and good axtraction yield (which was not satisfactory when using MeOH percentage higher than 20%).
For elution MeCN and MeOH were tested ; best results were obtained using 1.5 mL of MeOH