Immunologic trapping in supported liquid membrane extraction

To obtain a high degree of selectivity in sample preparation, supported liquid membrane (SLM) extraction was combined with immunologic recognition. The SLM employs a hydrophobic polymer for supporting the immobilization of an organic solvent, thus forming a nonporous membrane. Said membrane separates the aqueous sample on one side (donor) from a receiving aqueous phase on the other (acceptor). The extraction involves the partitioning of neutral compounds between the sample solution, continuously pumped alongside the membrane, and the membrane. From the membrane, reextraction takes place into a second aqueous phase containing antibodies specific for the target compound(s). Hence, there is a formation of an antibody-antigen complex at the heart of the sample preparation (ImmunoSLM). When the immunocomplex forms, the antigen can no longer redissolve in the organic membrane, thus being trapped in the acceptor. Consequently, the concentration gradient of free antigen over the membrane is ideally unaffected, this being the driving force for the process. With a surplus of antibody, the concentration of analyte in the receiving phase will easily exceed the initial sample concentration. In this work, the so formed immunocomplex was quantified on-line, using a fluorescein flow immunoassay in a sequential injection analysis (SIA) setup. The outlined ImmunoSLM-SIA scheme was successfully applied for the extraction of 4-nitrophenol from spiked water solutions as well as from a spiked wastewater sample, indicating that the immunoextraction can be suitable when dealing with difficult matrixes.