Separating stereoisomers of di‐, tri‐, and tetrapeptides using capillary electrophoresis with contactless conductivity detection

Abstract

The separation and detection of small oligopeptides in CE with contactless conductivity detection were demonstrated. A strongly acidic separation buffer (0.5 M acetic acid) was employed in order to render the species cationic. Separation of the stereoisomers was achieved in typically 10–15 min by using either dimethyl‐β‐CD (DM‐β‐CD), (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid (18C₆H₄), a combination of the two substances, or of histidine, as buffer additives. Calibration curves were determined for isomers of Gly‐Asp and H‐Pro‐Asp‐NH₂, in the range of 0.05–0.5 mM and 0.1–1 mM, respectively, and were found to be linear. LODs were determined to be in the order of 1.0 μM. The determination of isomeric impurities down to about 1% was found possible. Species showing good separation could also be successfully determined on an electrophoretic lab‐on‐chip device, with analysis times of a few minutes.