Pillar MEMS columns for gas chromatography

Abstract

One of the promising directions in the field of analytical instrumentation is the development of microfluidic devices, which are systems of thin channels on the surface of various materials such as glass [1], silicon [2], various polymeric materials [3]. The use of gas chromatographic columns on the plane in the design of modern analytical devices leads not only to a reduction in the size of the devices, but also to a significant reduction in one cycle of analysis [4-7]. One of the ways to minimize the time of chromatographic analysis is the creation of columns (pillars) inside the channel, which can significantly increase the specific efficiency of such columns. The aim of this work was to develop, manufacture and study the chromatographic properties of MEMS columns of pillar type.

Comparison of MEMS columns of pillar and capillary types with the same channel topology showed that the efficiency of chromatographic separation for pillar-type columns is 30% higher than the efficiency of the capillary-type columns. This effect is achieved by decreasing the pressure drop and the contribution of the vortex diffusion in comparison with the MEMS columns of the capillary type. The presence of an ordered structure in the form of columns inside the capillary of the pillared MEMS columns results in a significant increase in the column efficiency compared to the microfluidic columns of the capillary type by reducing the contribution of longitudinal diffusion and mass transfer. As the carrier flow through the section containing the pillars, the mass transfer is reduced due to transverse diffusion, which leads to a decrease in the smearing of the chromatographic band. As the gas flow passes through the section where the columns are absent, there is a slight blurring of the chromatographic strip, which is substantially smaller than in the parabolic flow profile of the open capillary column. Thus, the smearing of the chromatographic strip in the semi-packed column is less than in the capillary column, which leads to an increase in the column efficiency.

Due to the increased efficiency, the time of one cycle of analysis of natural gas components on these columns is reduced by more than half and amounts to 1.7 min.