The Column - May 2007 - (Page 21)

May 2007 www.thecolumn.eu.com The Column Pesek and Matyska Etched Chemically Modified Capillaries: A Novel Separation Medium for Electrophoretic Analyses 1Department Joseph J. Pesek1 and Maria T. Matyska2 of Chemistry, San Jose State University, San Jose, California, USA, 2MicroSolv Technology Corporation, Eatontown, New Jersey, USA. This article describes a novel form of electrophoresis, where the inner walls of the capillaries are etched and then chemically modified. These columns display excellent biocompatibility, electroosmotic flow that can be changed from anodic to cathodic as a function of pH, high reproducibility and long lifetimes. A variety of separations including small basic molecules, peptides and proteins are reviewed. Capillary electrophoresis (CE) can be configured in a variety of formats, each with their own distinct features and capabilities. One recent column configuration combines a stationary phase for chromatographic interactions in an open tube, as well as using differences in electrophoretic mobility, to expand resolving power. The surface area of the inner wall of can be increased by a factor of 1000 or more and radial extensions of up to 5 µm in length can also be created.1 This process can partially alleviate the low capacity of the bare capillary and shorten the distance solutes must travel to interact with a stationary phase attached to the etched surface. In addition, elements from the etching reagent, nitrogen and fluoride, are also incorporated into the new surface matrix.2 Their presence decreases some of the strong adsorptive properties of the silanols, which makes the new surface more biocompatible. Further enhancements in capillary performance can be obtained from the bonding procedure used to modify the etched surface. To substantially eliminate the effects of Authors: Joseph J. Pesek and Maria T. Matyska E-mail: pesek@sjsu.edu residual silanols, a new surface is created that is composed primarily of silicon hydride. The selectivity of the capillary is achieved by attaching an organic moiety to the etched hydride surface via a hydrosilation process. The etching process results in a completely different surface matrix composed of silicon, oxygen, fluoride and nitrogen. Nitrogen in particular has a significant effect on the electrophoretic behaviour of the capillary. At low pH the nitrogens near the surface become protonated, giving an overall positive charge to the inner wall of the capillary. This results in reverse electroosmotic flow (EOF) under these conditions. As the pH is raised to less acidic conditions, the EOF passes through zero and then becomes cathodic as a result of the deprotonation of the nitrogens, ionization of the remaining silanols and the negatively charged fluoride species.2 The presence of these additional elements in the surface matrix does not interfere with the subsequent chemical modification. 21 http://www.thecolumn.eu.com

Table of Contents for the Digital Edition of The Column - May 2007

Contents
News
Using LC–MS to Extend the Time Window for Detecting Drugs
Zosimus
Market Trends and Analysis
Etched Chemically Modified Capillaries: Novel Separation Medium for Electrophoretic Analyses
Q&A
Shaping the Future
Special Section: Shidadzu - LC World Talk

The Column - May 2007