Implementation of droplet-membrane-droplet liquid-phase microextraction under stagnant conditions for lab-on-a-chip applications

In the current work, droplet-membrane-droplet liquid-phase microextraction (LPME) under totally stagnant conditions was presented for the first time. Subsequently, implementation of this concept on a microchip was demonstrated as a miniaturized, on-line sample preparation method. The performance level of the lab-on-a-chip system with integrated microextraction, capillary electrophoresis (CE) and laser-induced fluorescence (LIF) detection in a single miniaturized device was preliminarily investigated and characterized. Extractions under stagnant conditions were performed from 3.5 to 15 μL sample droplets, through a supported liquid membrane (SLM) sustained in the pores of a small piece of a flat polypropylene membrane, and into 3.5-15 μL of acceptor droplet. The basic model analytes pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted from alkaline sample droplets (pH 12), through 1-octanol as SLM, and into acidified acceptor droplets (pH 2) with recoveries ranging between 13 and 66% after 5 min of operation. For the acidic model analytes Bodipy FL C₅ and Oregon Green 488, the pH conditions were reversed, utilizing an acidic sample droplet and an alkaline acceptor droplet, and 1-octanol as SLM. As a result, recoveries for Bodipy FL C₅ and Oregon Green 488 from human urine were 15 and 25%, respectively.