SEPARATION OF NATIVE AMINO-ACIDS AT LOW PH BY CAPILLARY ELECTROPHORESIS

Amino acids are cations at low pH and can be readily separated by capi llary electrophoresis provided an alkanesulfonic acid is added to the electrolyte carrier. Formation of a positive net charge on the bare fu sed-silica surface at low pH was confirmed by measurement of an anodic electroosmotic flow. The addition of ethanesulfonic acid or octanesul fonic acid to the electrolyte carrier causes a reversal of the EOF. A mechanism is proposed in which the alkanesulfonic acid adsorbs to the positively-charged capillary wall through electrostatic attraction. Ad sorption of a second molecule of alkanesulfonate by hydrophobic attrac tion to the carbon chain forms a negatively-charged coating on the cap illary wall. The alkanesulfonate also imparts selectivity to the syste m by participation in ion-pairing interactions with the native amino a cids to improve resolution. The CE separation of a mixture of the twen ty common amino acids at pH 2.8 with direct absorbance detection at 18 5 mm resulted in 17 amino acid peaks in 20 minutes with a 30 kV applie d voltage. The effect of several variables was studied including elect rolyte carriers containing different alkanesulfonic acids, the influen ce of pH, applied voltage, and concentration of electrolyte carrier.