Selective electromembrane extraction at low voltages based on analyte polarity and charge

Electromembrane extraction (EME) at low voltage (0–15 V) of 29 different basic model drug substances was investigated. The drug substances with log P < 2.3 were not extracted at voltages less than 15 V. Extraction of drug substances with log P ≥ 2.3 and with two basic groups were also effectively suppressed by the SLM at voltages less than 15 V. Drug substances with log P ≥ 2.3 and with one basic group were all extracted at low voltages and with a strong compound selectivity which appeared to have some influence from the polar surface area of the compound. For this group of substances, recoveries varied between 0 and 23% at 5 V, whereas, recoveries varied between 5.5 and 51% at 15 V. Based on mass transfer differences related to charge, polarity, and polar surface, highly selective extractions of drug substances were demonstrated from human plasma, urine, and breast milk. An initial evaluation at low voltage (5 V) was compared with similar extractions at a more normal voltage level (50 V), and this supported that reliable data can be obtained under these low-voltage (mild) conditions by EME.