Utilization of the sol–gel technique for the development of novel stationary phases for capillary electrochromatography on a chip

Abstract

Capillary electrochromatography (CEC) appears ideally suited for high performance separations at small scale, i.e. on a chip. Problems with the reproducible production of the required m-HPLC column, but also the lack of commercially available m-CEC instruments have prevented many putative applicants of this promising technique from entering the ®eld. In this paper, a fast and easy way to produce selfcontaining open-tubular m-CEC columns (C 8 -moieties for reversed phase applications) by the sol±gel technique is described. The corresponding chips were designed to be compatible with a commercial system for capillary electrophoresis (namely a Beckman P/ACE 5500 system with diode array detection). Method development and application hence bene®ted from the injection and the detection options of this setup. The separation of a mixture of three uncharged analytes (polycyclic aromatic hydrocarbons) by the chip is given as example. Under optimized conditions, the performance of the chip appeared to be comparable or better than that of capillary-based CEC columns of the same kind. #

Liquid chromatography on chip

“…The very first LC-dedicated microsystem was fabricated in 1990 by Manz et al [5][6][7][8]. Since 2005, coating of microsystems has been performed using many techniques such as sol-gel [9] or nanoparticles deposition [10], but most of these surface treatments were used to reduce the adsorption character of microsystem bulk material, whose contribution is especially detrimental when analyzing biological solutes such as proteins.…”

“…Very few strategies have been brought up to actually perform selective adsorption or partitioning onto the wall surface for openchannel chromatography. Functionalization of glass chips with C 8 -tetraethylorthosilicate has been performed [11] following a previously reported procedure [6]. On the resulting openchannel chip-LC, the authors demonstrate the RP behavior of the coated stationary phase through separation of phenol and methylphenol.…”

Continuous sampling and analysis by on-chip liquid/solid chromatography

“…This procedure yields a thin coating of a silica hybrid gel on the column wall which contains the functional layer. In our case this is a mixture of tetraethoxysilane/tetraethoxysilane-C 8 that yields a C 8 layer acting as stationary phase, following the preparation shown by Constantin et al [36,37]. The sol-gel precursor solution is pumped into the column, allowed to stay for several minutes and then forced out of the column by nitrogen overpressure before the chip is dried overnight under nitrogen flow at 120 • C. This process yields …”

Integration of nanoporous membranes for sample filtration/preconcentration in microchip electrophoresis

“…These areas have included a variety of separation technologies based on CE [1][2][3][4][5][6] and LC [7][8][9], biochemical reactions such as derivatization [10][11][12], PCRs [13][14][15][16], and enzyme digestion [17][18][19] as well as fluidic components named valves and pumps [20][21][22][23].…”