Determination of melamine in dairy products using electromembrane-LPME followed by HPLC

This study presents the application of electromembrane microextraction technique combined with HPLC-UV detection for fast extraction-preconcentration and determination of melamine in dairy products. It is based on the extraction of charged melamine molecules migrated from 6.5 mL feed solution through a liquid membrane immobilized in the pores of a hollow fiber into 20 μL of the acceptor solution. The best performance was achieved by using 2-nitrophenyloctylether, tris-(2-ethylhexyl) phosphate (10%) and di-(2-ethylhexyl)phosphate (10%) as the extraction solvent; application of a potential of 90 V as the driving force and by adjusting the pH of feed and receiving phases at 5.5 and 1, respectively. The working range was 7-8000 ng mL−1, with detection limit of 2.0-5.8 ng mL−1. The enrichment factor was in the range 82-192. Intra- and inter-day relative standard deviations were less than 6.6%. Extraction and relative recoveries for different samples were between 25-59% and 85-95%, respectively.