An Integrated Fritless Column for On-Chip Capillary Electrochromatography with Conventional Stationary Phases

Abstract

A new polymer device for use with conventional particulate stationary phases for on-chip, fritless, capillary electrochromatography (CEC) has been realized. The structure includes an injector and a tapered column in which the particles of the stationary phase are retained and stabilized. The chips were easily fabricated in poly-(dimethylsiloxane) using deep-reactive-ion-etched silicon masters, and tested using a capillary electrophoretic separation of FITC-labeled amino acids. To perform CEC, the separation channel was packed using a vacuum with 3-µm, octadecylsilanized silica microspheres. The packing was stabilized in the column by a thermal treatment, and its stability and quality were evaluated using in-column indirect fluorescence detection. The effects of voltage on electro-osmotic flow and on efficiency were investigated, and the separation of two neutral compounds was achieved in less than 15 s.The use of microfabricated fluidic substrates has become increasingly well-established for liquid-phase analysis in recent years. This is particularly true for electrokinetically driven separations, where etched microchannels provide an easy route to reduced column diameters and, hence, increased efficiencies and decreased solvent/sample consumption. 1 As with narrow bore (<75 µm), fused-silica capillaries used in conventional capillary electrophoresis (CE) instrumentation, the high surface-to-volume ratios of these chip-based systems enable good dissipation of Joule heat. However, the shortest capillary that can be used in a benchtop instrument is generally no less than 30 cm long, which leads to typical applied electric field strengths on the order of a few hundred volts per cm. With chip CE, working with much shorter separation channels is facilitated, allowing electric fields of 500-1000 V/cm and decreased analysis times as a result. [2][3][4][5] The integration of picoliter-volume injection elements into etched CE devices is a further unique feature of the chip format. Microfluidic devices operated using pressure-driven flow 6,7 and centrifugal pumping [8][9][10][11] have also been reported, expanding the range of possible analyses. The microfluidic approach should generally enable high throughput applications, 12-14 as well as a high level of automation for real-time testing at the point of care (POC). [15][16][17] The many advantages of microfabricated devices for ultrasmallscale analysis have been demonstrated with a wide variety of examples, including sample preconcentration, 18,19 cell handling, 20,21

Pressure-Driven Sample Injection with Quantitative Liquid Dispensing for On-Chip Electrophoresis

“…Next, the designed channel patterns were transferred to silicon wafers using a mask aligner (ES 20, Nanometric Technology, Inc., Japan). After developing in ethyl lactate (Wako Pure Chemical Ind., Osaka, Japan), the surface of masters were treated with dimethyloctadecylchlorosilane 23 (Shin-Etsu Chem. Co., Japan) for the easy peeling off of a PDMS replica.…”

Capillary electrophoresis microchip coupled with on-line chemiluminescence detection

“…Since the first realization of -TAS by Manz et al [3] in 1990, this approach has caused a profound revolution in the conception of analytical instrumentation. Many studies [4][5][6][7] have been made in this field, and it had been shown to offer enormous practical potential in chemical and biochemical analyses.…”

Integration of ground aerogel particles as chromatographic stationary phase into microchip

“…Silica aerogels hold records for the lowest However, only a few chip-based chromatographic systems have 50 been reported so far as compared to chip-based capillary elec-51 trophoretic (CE) devices, which is mainly due to technical problems 52 inherent in the former [7,8]. Most microfluidic devices are based on 53 open tubular flow designs and only a few involve packed-bed chips 54 due to the difficulty in preparing frits [9,10]. Recently, this prob-55 lem has been excellently addressed [11], however, the high-tech 56 manufacturing of the three-laminated polyimide layers chip (use 57 of laser, micromachined frit) is not possible for the large majority 58 of the researchers.…”

“…The packing was prepared daily, and it was preconditioned with that it was only necessary to taper a rigid capillary [9] or flexible 157 microfluidic channel [12] to approximately 10 m (inner diameter) 158 to achieve the keystone effect [9] and to retain 3 m sized particles. It…”