On-chip electro membrane extraction with online ultraviolet and mass spectrometric detection

Electro membrane extraction was demonstrated in a microfluidic device. The device was composed of a 25 μm thick porous polypropylene membrane bonded between two poly(methyl methacrylate) (PMMA) substrates, each having 50 μm deep channel structures facing the membrane. The supported liquid membrane (SLM) consisted of 2-nitrophenyl octyl ether (NPOE) immobilized in the pores of the membrane. The driving force for the extraction was a 15 V direct current (DC) electrical potential applied across the SLM. Samples containing the basic drugs pethidine, nortriptyline, methadone, haloperidol, loperamide, and amitriptyline were used to characterize the system. Extraction recoveries were typically in the range of 65-86% for the different analytes when the device was operated with a sample flow of 2.0 μL/min and an acceptor flow of 1.0 μL/min. With the sample flow at 9.0 μL/min and the acceptor flow at 0.0 μL/min, enrichment factors exceeding 75 were obtained during 12 min of operation from a total sample volume of only 108 μL. The on-chip electro membrane system was coupled online to electrospray ionization mass spectrometry and used to monitor online and real-time metabolism of amitriptyline by rat liver microsomes.