Rapid analysis of peptides and amino acids by CE-ESI-MS using chemically modified fused-silica capillaries

The objective of this study was to prepare a coated capillary to achieve rapid analysis of peptides and amino acids (AAs) by CE-ESI-MS. The coated capillary was prepared by chemical modification of the fused silica (FS) capillary with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) via a silanization reaction followed by an on-column in situ graft polymerization. In preparing capillary coating, AMPS was introduced for the following two purposes: first, to achieve strong and stable EOF in a wide pH range, and second, to obtain good repeatability of separations of peptides and AAs by reducing their adsorption to the FS capillary. The inner wall morphology, the characteristics of EOF, and the performances of coated capillary including separation ability, repeatability, and stability were investigated in detail and evaluated by analyses of four peptides (D-Ala-D-Ala, Gly-Gly-L-Leu, Gly-D-Phe, and L-Leu-D-Leu) and three AAs (glycine, glutamic acid, and phenylalanine), respectively. Under the optimized conditions, the analysis times of four peptides and three AAs in the coated capillary were 5.6 and 6.0 min, respectively, i.e. much shorter than those in the bare-FS capillary, 20 and 26 min, respectively. These coated capillaries were shown to be well suitable for CE coupling with ESI-MS to analyze peptides and AAs thanks to high separation power, short analysis times, good repeatability and high stability.