In preparation for extraction, sample and acceptor solution were loaded into their respective vials, for each extraction cell. Unless otherwise stated both volumes were 250 µL. The sample comprised a neat standard (analytes spiked into pure buffer) or spiked human plasma (diluted 1:1 v/v with suitable buffer), while the acceptor was a buffer solution. A polypropylene membrane was placed in the Teflon union and secured by tightly screwing the sample vial into place. Next, 9 µL liquid membrane solvent was pipetted onto the supporting polypropylene membrane and became immobilized in the pores. The acceptor vial was screwed into the union, and the extraction cell was placed in the 10-position holder, the lid was attached, and extraction was initiated by simultaneous application of 750 RPM agitation and extraction voltage (variable). For extraction of acidic analytes, the positive terminal (anode) was connected to the acceptor vial, while the negative terminal (cathode) was connected to the sample vial. Unless otherwise stated, extraction experiments were performed in triplicate. Following extraction, the acceptor solution was analyzed by UHPLC-MS/MS.