The aim of this study was to investigate the influence of organic solvents on the electrophoretic separation of phenylethylamines. The background electrolyte composition was adjusted with different protic (methanol, ethanol, and 2-propanol) and aprotic (dimethyl sulfoxide and acetonitrile) solvents. Two groups of analytes were studied. The first group contained phenylethylamines with an amine group only, DL-1-phenylethylamine and amphetamine. The second group represented phenylethylamines with both amine and phenolic hydroxyl groups, dopamine and tyramine. Experiments revealed no or minor influence of the organic modifiers on the electromigration behavior of the analytes from the first group (containing only the amine group) and a drastic effect on the second group (containing the additional phenolic hydroxyl group). Dopamine and tyramine showed various electrostatic, hydrophobic, and hydrogen-bonding interactions with both protic and aprotic organic solvents. The dependence of the electrophoretic mobility of dopamine and tyramine on the concentration of the organic solvents provided direct evidence of the formation of hydrogen bonds between dopamine or tyramine and the organic solvent. The baseline separation was achieved by the addition of at least 20% v/v of organic solvent (protic or aprotic) to the background electrolyte. The analyte migration time repeatabilities were within 0.7-4.1% for absolute and 0.2-1.9% for normalised migration times. The proposed bonding mechanism and behavior of phenylethylamines were examined and confirmed by NMR spectroscopy.
Keywords: Capillary electrophoresis; Cationic solutes; Electromigration behavior; Hydrogen-bonding interaction; Solvation.
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