A semi-packed gas chromatography column with high-density elliptic cylindrical posts

A micro gas chromatographic column with in-situ growing macro-porous silicon as stationary phase support layer

This paper reports a micro gas chromatographic column (μGCC) with in-situ growing macro-porous silicon as the stationary phase support layer. The macro-porous silicon stationary phase support layer (MPSL) with uniform thickness was fabricated in-situ on the inner surface of the μGCC channels by metal-assisted chemical etching. In order to avoid the negative effect of uneven thickness of the stationary phase, a 10 nm alumina film was deposited as the stationary phase on the MPSL using the atomic layer deposition technique. The macro-porous structure and high specific surface area of the MPSL provide longer diffusion paths and larger mass transfer interfaces for the analytes, which reduces the longitudinal gas diffusion and mass transfer resistance, thus improving the column efficiency. The μGCC with the MPSL achieved a 1306.7 % increase in the theoretical plate number and a 195.0 % improvement in the resolution for n-nonane compared with the μGCC without the MPSL.

Impact of silicon substrate on micro gas chromatographic column using ALD alumina as the stationary phase

Due to the high conformal films, atomic layer deposition (ALD) alumina has been used as a uniform stationary phase or support layer of stationary phase for micro gas chromatographic column. However, the severe tailing of chromatographic peaks appears when ALD alumina is used as the stationary phase. Recently, an H-diffusion model was proposed to explain the H accumulation phenomenon of ALD alumina films. Compared with the normal-resistance silicon substrates, the ALD alumina films based on low-resistance silicon substrates have fewer H impurities, which may further improve the tailing of chromatographic peaks and the theoretical number of plates. In this paper, a micro gas chromatographic column based on the low-resistance silicon (LR-μGCC) substrate (resistivity, 0.001-0.005 Ω·cm) using alumina deposited by atomic layer deposition as the stationary phase is reported. Compared with normal-resistance silicon substrates (resistivity, 1-10 Ω·cm), the micro gas chromatographic columns (μGCC) prepared on low-resistance silicon substrates have a higher separation performance. The test results showed that the LR-μGCC increased the theoretical plate number of alkane mixtures (n-hexane, n-octane, n-nonane, and n-decane) by 20.9%, 74.8%, 139.4%, and 55.4%, respectively, and reduced the tailing factor by 13.0%, 41.8%, 48.6%, and 49.1%, respectively.

A microchip gas chromatography column assembly with a 3D metal printing micro column oven and a flexible stainless-steel column

In this work, a microchip gas chromatography (GC) column assembly utilizing a three-dimensional (3D) printed micro oven and a flexible stainless steel capillary column was developed. The assembly's performance and separation capabilities were characterized. The key components include a 3D printed aluminum plate (7.50 × 7.50 × 0.16 cm) with a 3-meter-long circular spiral channel, serving as the oven, and the column coiled on the channel with an inner diameter of 320 μm and a stationary phase of OV-1. A heating ceramic plate was affixed on the opposite side of the plate. The assembly weighed 40.3 g. The design allows for easy disassembly, or stacking of heating devices and columns, enabling flexibility in adjusting column length. When using n-C13 as the test analyte at 140 °C, a retention factor (k) was 8.5, and 7797 plates (2599 plates/m) were obtained. The assembly, employing resistance heating, demonstrated effective separation performance for samples containing alkanes, aromatics, alcohols and ketones, with good reproducibility. The reduction in theoretical plates compared to oven heating was only 2.95 %. In the boiling point range of C6 to C18, rapid temperature programming (120 °C/min) was achieved with a power consumption of 119.512 W. The assembly was successfully employed to separate benzene series compounds, gasoline and volatile organic compounds (VOCs), demonstrating excellent separation performance. This innovative design addresses the challenges of the complexity and low repeatability of the fabrication process and the high cost associated with microchip columns. Furthermore, its versatility makes it suitable for outdoor analysis applications.

Characterization of semi-packed columns with different cross section in high-pressure gas chromatography

Hydrodynamics, efficiency, and loading capacity of two semi-packed columns with different cross sections (NANO 315 µm x 18 µm; CAP 1000 µm x 28 µm) and similar pillar diameter and pillar-pillar distance (respectively 5 µm and 2.5 µm) have been compared in high-pressure gas chromatography. A flow prediction tool has been first designed to determine pressure variations and hold-up time across the chromatographic system taking into account the rectangular geometry of the ducts into the semi-packed columns. Intrinsic values of Height Equivalent to Theoretical Plate were determined for NANO and CAP columns using helium as carrier gas and similar values have been obtained (30 µm) for the two columns. Loading capacity of semi-packed columns were determined for decane at 70 °C using helium, and the highest value was obtained from CAP column (larger cross section and stationary phase content). Finally, significant HETP improvement (down to 15 µm) and peak shape were observed when carbon dioxide was used as carrier gas, suggesting mobile phase adsorption on stationary phase in high pressure conditions.

A semi-packed gas chromatographic column with staggered elliptic cylindrical post arrays

A semi-packed gas chromatographic column has the advantages of high specific surface area and low column pressure. We report that the stagnation regions formed in the adjacent posts along the channel of the semi-packed columns can decrease the area and height of chromatographic peaks, which makes it difficult to detect low-concentration mixed gases. A semi-packed column with staggered elliptic cylindrical post arrays (SC-S) made using a micro-electro-mechanical system technique is presented, and the separation performance of SC-S is compared with that of a semi-packed column with aligned elliptic cylindrical post arrays (SC-A). The simulation results show that the width of stagnation regions in SC-S is 86.89% smaller than that in SC-A. The experimental results indicate that the area and height of chromatographic peaks increased as stagnation regions reduced. In the separation of the alkane mixture from C8 through C10 with 10 ppm concentration, the chromatographic peak of decane was hardly identified in SC-A while the chromatographic peak in SC-S was still clearly visible. The chromatographic peak heights of octane and nonane were increased by 65.06% and 130.00%, respectively, in SC-S. The peak areas of octane and nonane were increased by 120.45% and 168.18%, respectively.