Carbon nanotube based separation columns for high electrical field strengths in microchip electrochromatography

Abstract

Electrically insulated carbon nanotube (CNT) based separation columns have been fabricated that can withstand an electrical field strength of more than 2.0 kV cm(-1) without bubble formation from electrolysis. The carbon nanotubes were grown in a pillar array defined by photolithographic patterning of the catalyst layer used for synthesis of the nanotubes. Multiwall carbon nanotubes are inherently electrically conductive and cannot be used as a continuous layer in the microfluidic channels, without short circuiting the electrical field in the separation column, when the field strength is more than a couple of 100 V cm(-1). Here, the carbon nanotubes are grown in an array of hexagonal pillars, where the nanotubes in the individual pillars are not in direct electrical contact with the nanotubes of the adjacent pillars. This makes it possible to increase the electrical field strength from around 100 V cm(-1) to more than 2.0 kV cm(-1) and thereby to use the CNT columns for electrokinetic separations with the high electrical field strengths that are typically used in this application. An electrochromatographic separation of two Coumarin dyes was demonstrated on the CNT column with an acetonitrile content of 90%.

Preparation and evaluation of mesoporous silica layers on radially elongated pillars

“…Since the group of Regnier first used perfectly ordered pillars as the stationary-phase support structure in chromatography in 1998 [2], pillar array columns (PACs) have been studied intensively by a limited number of research groups [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. A dramatic reduction of the disorder related eddy dispersion or A-term of the van Deemter equation has been consistently demonstrated throughout the past decade, but also the freedom in external porosity, flow-through pore shape and channel depth turned out to be features that can be exploited to further tune and improve the column considerably.…”

“…Bottom up approaches enable creation of porous layers of another material on pillars. Techniques to use carbon nanotubes (CNTs) for PACs have been developed by the group of Kutter [4,5] and the group of Vinet [16,17], and their work has shown that CNTs can be used as a stationary phase in reversed phase CEC and LC. The use of CNTs is quite unique in the field of chromatography, on the other hand, silica, a traditional material in this field, is often selected as the material of the porous layers prepared by bottom up approaches.…”

Integrating Carbon Nanotubes into Microfluidic Chips for Separating Biochemical Compounds

“…In the measurements, the microfluidic channels were filled with a 50 % 10 mM Tertraborate buffer (pH = 9.2) / 50 % acetonitrile solution. For pillar length of 8.0 µm, E can be applied up to 2 kV/cm without bubble formation, which was same as the one measured from the channel without CNTs [9]. Higher E will result in faster fluid flow velocity and smaller plate height, thus making the chips have sharp emission peak and better separation efficiency.…”

CE and nanomaterials – Part II: Nanomaterials in CE

“…The chip was successfully tested to isolate a glycosylated protein using concanavalin A immobilized onto the nanotube bed. Moreover, immobilization of the CNTs enabled the application of a notably high electrical field strength, thereby eliminating bubble formation .…”