Investigation of the novel mixed‐mode stationary phase for capillary electrochromatography. II. Separation of amino acids and peptides on sulfonated naphthalimido‐modified silyl silica gel

Abstract

The potential of 3-(4-sulfo-1,8-naphthalimido)propyl-modified silyl silica gel (SNAIP) as a mixed-mode stationary phase for capillary electrochromatography (CEC) was investigated for the separation of charged analytes, taking four amino acids (tyrosine, phenylalanine, tryptophan, histidine) as model analytes. The elution process of these charged analytes in CEC with SNAIP was dominated by a combination of both electrophoretic process and chromatographic process involving hydrophobic as well as electrostatic interactions. In order to study the retention mechanism, the CEC retention factor k* and the velocity factor ke* were measured for the amino acids, which allowed the assessment of the respective contribution from the differential processes underlying the separation. Migration and retention could be mediated by changing various mobile phase compositions, including buffer pH, buffer concentration, and concentration of organic solvent. Based on the results obtained by separation of the amino acids, the separation of eight peptides (Gly-Val, Gly-Phe, Gly-Ile, Gly-His, Gly-Lys, Lys-Lys, Gly-Gly-Gly, Gly-Gly-His) was attempted. A good separation was achieved under an isocratic elution with a mobile phase consisting of 35 mM phosphate buffer (pH 3.8) and 40% methanol.

Determination of organic acids by CE and CEC methods

“…Lin et al [18] separated underivatized AAs on packed and monolithic capillary columns and used chemiluminescence detection based on the principle of the luminol-H 2 O 2 -Cu(II)-amino acid system and a modified on-column coaxial flow cell for the sensitive detection of these compounds. The development of a novel mixed mode stationary phase for the separation of AAs was reported by Ohyama et al [114]. The 3-(4-sulfo-1,8-napthalimido)propylmodified silica used in this study allowed the separation of AAs and small peptides without derivatization.…”

Recent progress in polar stationary phases for CEC

“…Ohyama et al [59] also studied the separation of charged analytes, taking four amino acids (tyrosine, phenylalanine, tryptophan, histidine) and eight peptides (Gly-Val, GlyPhe, Gly-Ile, Gly-His, Gly-Lys, Lys-Lys, Gly-Gly-Gly, GlyGly-His) as model analytes, on SNAIP as a mixed-mode stationary phase in CEC. The migration behavior of these charged analytes was mainly dominated by a combination of both electrophoretic process and chromatographic process involving hydrophobic as well as electrostatic interactions.…”

Recent applications in capillary electrochromatography

“…A mixed-mode CEC stationary phase was prepared by Ohyama et al [26], who modified an aminopropyl silyl silica (5 mm particles) with a sulfonated naphthyl compound (see Fig. 4).…”

“…The mixed-mode CEC stationary phase modified with a sulfonated naphthyl compound described earlier [26] was also used to separate nucleosides and nucleic acid bases [47]. A step gradient was used to shorten the analysis time.…”