Electromembrane extraction of peptides based on hydrogen bond interactions

Background: Electromembrane extraction (EME) of peptides reported in the scientific literature involve transfer of net positively charged peptides from an aqueous sample, through a liquid membrane, and into an aqueous acceptor solution, under the influence of an electrical field. The liquid membrane comprises an organic solvent, containing an ionic carrier. The purpose of the ionic carrier is to facilitate peptide solvation in the organic solvent based on ionic interactions. Unfortunately, ionic carriers increase the conductivity of the liquid membrane; the current in the system increases, the electrolysis in sample and acceptor is accelerated, and the extraction system tend to be unstable and suffers from drifting pH. Results: In the present work, a broad selection of organic solvents were tested as pure liquid membrane for EME of peptides, without ionic carrier. Several phosphates provided high mass transfer, and tri(pentyl) phosphate was selected since this solvent also provided high operational stability. Among 16 different peptides used as model analytes, tri(pentyl) phosphate extracted those with net charge +1 and with no more than two polar side chains. Tri(pentyl) phosphate served as a very strong hydrogen bond acceptor, while the protonated peptides were hydrogen bond donors. By such, hydrogen bonding served as the primary interactions responsible for mass transfer. Tri(pentyl) phosphate as liquid membrane, could exhaustively extract leu-enkephalin, met-enkephalin, and endomorphin from human blood plasma and detected by LC-MS/MS. Calibration curves were linear (r2 >

Automated summary

Electromembrane extraction (EME) of peptides involves the transfer of positively charged peptides from an aqueous sample through a liquid membrane into an aqueous acceptor solution under an electrical field. However, the use of ionic carriers in the liquid membrane increases the system's conductivity and leads to instability and drifting pH. In this study, a selection of organic solvents without ionic carriers was tested as pure liquid membrane for EME of peptides, and tri(pentyl) phosphate was found to be the most suitable solvent. It extracted peptides with a net charge of +1 and no more than two polar side chains, and was able to extract leu-enkephalin, met-enkephalin, and endomorphin from human blood plasma.