Characterization of open tubular capillary electrochromatography columns for the analysis of synthetic peptides using isocratic conditions

In this paper, we report on investigations related to the performance chara cteristics of two different types of etched chemically (n-octadecyl- and ch olesterol-) modified capillaries in the open tubular format of capillary el ectrochromatography (CEC) for the analysis of synthetic peptides. The resul ts confirm that the nature of the surface chemistry used to modify the capi llary wall and type of chemically bonded group employed can affect the sele ctivity as well as the resolution of peptide samples. The results are consi stent with the participation of selective peptide interactions with the bon ded phase, although other factors, such as the morphology of the capillary waft surfaces, appear to be also involved. Moreover, several surprising obs ervations related to peptide-specific multizoning effects have been observe d. Additional experimental variables that can also be utilized to affect th e retention of peptides in this approach to OTCEC include the type and perc entage of organic solvent modifier employed in the eluent and the pH of the buffer system. To evaluate the reproducibility of different batches of the n-octadecyl-and cholesterol-modified capillaries and the stability of the chemically modified surface, the OTCEC selectivity and peak shape behavior of two small basic molecules (serotonin and tryptamine) and two proteins (t urkey and chicken lysozyme) were also investigated. Finally, the use of the "bubble" cell technology for creating the detector window has been shown t o provide significantly higher detection sensitivity with peptides, as comp ared with the conventional capillary format.