SUPPORTED LIQUID MEMBRANES FOR THE EXTRACTION OF PHENOLIC-ACIDS FROM CIRCULATING NUTRIENT SOLUTIONS

A supported liquid membrane system has been developed for the extracti on of phenolic acids for circulating nutrient solutions for tomato cul ture. A porous PTFE membrane is impregnated with an organic solvent, w hich thus forms a barrier between two aqueous phases. The analytes are extracted from an aqueous donor solution into the hydrophobic membran e and then back extracted into a second aqueous solution, the acceptor , were the analytes are irreversible trapped. By pumping the donor and keeping the acceptor stagnant, an enrichment of analytes in the accep tor is achieved. The final determination is performed with liquid chro matography and W-detection utilised with a PRP-I packed precolumn repl acing the injection loop. The stability of five phenolic acids (p-hydr oxy benzoic acid, vanillic acid, caffeic acid, p-coumaric acid and fer ulic acid) in the nutrient solutions during various storage conditions is reported. High flow rates (up to 6.5 mL/min) are for the first tim e reported with the SLM-technique, which gives detection limits around 1 nM after 30 minutes enrichment of a number of different phenolic ac ids.