Peptide characterization with a sulfoethyl aspartamide column.

A strong cation-exchange (SCX) high-performance liquid chromatography column (sulfoethyl aspartamide, 200 x 4.6 mm) was used to analyze more than 50 peptides, ranging in length from 5 to 20 residues. These data show that the elution positions of the peptides increase monotonically with the number of positively charged residues. [A 60-min linear gradient of 0 to 100% eluent B at 1 ml/min was used, where eluent A is 5 mM phosphate (pH 3.0)-acetonitrile (75:25) and eluent B is eluent A + 0.5 M sodium chloride.] A comparison of SCX with a standard C18 reversed-phase (RP) column [60-min linear gradient of 0 to 60% B at 1 ml/min, where eluent A is 0.1% trifluoroacetic acid (TFA), and eluent B is 0.095% TFA-acetonitrile (10:90)] further demonstrates the utility of SCX in peptide characterization. SCX separated an (Arg)3-containing peptide from the Arg-deleted peptide while RP could not. In addition, SCX and RP resolved the methionine oxidation products of ACTH (4-10) (RP: Met [O] less than Met [O2] less than Met; SCX; Met [O] less than Met less than Met [O2]), suggesting a mixed-mode mechanism for the ion-exchange system. Finally, SCX separated the sulfated and non-sulfated forms of cholecystokinin (26-33) and Leu-enkephalin as well as the N-terminal acetylated forms of neurotensin (8-13) and angiotensinogen (1-14) from the respective unmodified peptides.