Remaining aqueous phase was extracted three
times by 600 mL of moderately polar mixture of diethyl ether and
ethyl acetate (3:2), organic extracts were collected in new vials and
dried with the use of anhydrous sodium sulphate. Derivatisation
reactionwas carried out by addition of 80 mL of derivatisation agent -
phenyloboronic acid (PBA) into the collected extracts. In order to
enhance the reaction ultrasound treatment was applied for 5 min.