Solvent-free electromembrane extraction: A new concept in electro-driven extraction

A solvent-free electromembrane extraction (SF-EME) device was developed. A thin polyvinylidene difluoride (PVDF) membrane placed at the end of an L-shaped glass tube acted as an analyte collector and was inserted into the sample solution. Under an applied voltage of 110 V, cationic peptides in the sample solution moved toward the negative electrode inside the L-shaped glass tube and were trapped by the membrane at the end of the tube. After 1 min of extraction, 3 μL of α-cyano-4-hydroxycinnamic acid (CHCA) solution was applied on top of the membrane, and then the membrane was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS). The parameters affecting the extraction efficiency, such as the type of membrane, applied voltage, pH range, and extraction time, were optimized. Under optimal extraction conditions, the calibration curves of angiotensin II and Arg-vasopressin were linear over concentration ranges of 0.50-30.00 nM and 0.20-25.00 nM, respectively. The limits of detection (LODs) at a signal-to-noise ratio of 3 were 0.15 and 0.06 nM with enhancement factors of 209 and 118 for angiotensin II and Arg-vasopressin, respectively. The application of this method to the determination of peptides in complex matrix solutions was also successfully demonstrated.