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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. [ABSTRACT FROM AUTHOR]

• A semi-packed column with high-density elliptic cylindrical posts was developed. • The surface area of SC HECP is 71% larger than SC CP. • The aspect ratio of SC HECP is 76% larger than SC CP. • Higher surface area and aspect ratio leads to better performance. Semi-packed columns are microfabricated gas chromatography columns which have a large surface area and high aspect ratio. In this paper, a new semi-packed column with high-density elliptic cylindrical posts (SC HECP) made by a micro-electro-mechanical system (MEMS) technique was reported. Compared to a semi-packed column with cylindrical posts (SC CP) under the same effective width, the surface area and aspect ratio of SC HECP were improved by 71.19% and 76.47%, respectively. To compare the performance of these two semi-packed columns, SC HECP and SC CP were fabricated. A 10-nm thick alumina film was deposited as the stationary phase by atomic layer deposition technique to ensure the uniformity and repeatability of the stationary-phase film. A contrast experiment was conducted, and the results showed that compared with SC CP, better separation performance was realized in SC HECP due to the increase in surface area and aspect ratio. The number of theoretical plates of nonane was increased by 541.84%, and the tailing factor was decreased by 54.31%. [ABSTRACT FROM AUTHOR]

The micro gas chromatography column (μGCC) is one of the key components of the miniaturized gas chromatography system. However, light alkanes are difficult to be separated by a micro gas chromatography column, especially for methane and ethane, because the length of μGCC is limited by the area of a silicon substrate. More importantly, the heterogeneous microchannel surface formed by silicon glass bonding causes uneven stationary phase coating and the forces between the untreated microchannel surfaces and the stationary phase materials are weak, which will prevent the improvement of separation performance. In this paper, a micro gas chromatography column (μGCC) with uniform HKUST-1 stationary phase is reported. Significantly, an alumina film prepared by the atomic layer deposition (ALD) technique is used to homogenize the heterogeneous microchannels. The alumina is a hydrophilic material and the alumina made by the ALD technique is uniform. The forces between hydrophilic alumina film and HKUST-1 are strong, which can greatly improve the coating uniformity of the hydrophilic stationary phase HKUST-1. The test results show that the μGCC could baseline separate the light alkane mixtures (CH 4 , C 2 H 6 , C 3 H 8 , and C 4 H 10) at the high testing temperature of 120 °C. The maximum resolution of the difficult-separated methane and ethane reached 19.2, which is 108 % higher than the μGCC using the same stationary phase without homogenizing the microchannel inner surface. The μGCC uses ALD alumina film to homogenize the microchannel inner surface; meanwhile, hydrophilic ALD alumina has a strong electrostatic attraction with the hydrophilic stationary phase HKUST-1. Homogeneous microchannel surface and strong electrostatic attraction are favorable to obtain uniform stationary phase which greatly improves the separation performance, resulting in a large resolution for methane and ethane. The μGCC has broad application prospects in light alkane separation. [Display omitted] • A novel μGCC with a homogeneous microchannel. • The uniform distribution of the HKUST-1 stationary phase is obtained. • Baseline separation of light alkanes (C1–C4) at 120 °C is obtained. • The resolution of methane and ethane can reach 19.2. [ABSTRACT FROM AUTHOR]

The gas chromatography column is one of the key components of the gas chromatograph and typically be miniaturized using micro-electro-mechanical system (MEMS) technology. Due to the limited area of the Si wafer, the column length of micro gas chromatographic column (μGCC) is usually much smaller than that of commercial chromatographic columns. Therefore, it is always difficult to use μGCCs to separate small molecule gas components such as light hydrocarbons. More importantly, the heterogeneous microchannel surface formed by silicon glass bonding causes uneven stationary phase coating, further preventing the improvement of separation performance. In this paper, a novel all-glass based μGCC with 2 m length for the separation of light hydrocarbons is proposed. The microchannels of the μGCC were directly prepared in the glass substrate by ultrafast laser assisted chemical etching (ULAE). The all-glass microchannels make the coating of the hydrophilic metal-organic frameworks (MOFs) stationary phase continuously because of the homogeneous material composition. Therefore, a widely used copper based hydrophilic MOFs HKUST-1 was used as stationary phase for coating and testing. The test results show that the μGCC which is an open tubular column can realize the baseline separation of light hydrocarbons at 100 °C. And the resolution of difficult separated compounds, methane and ethane, can reach 12.98, which is 201.86 % higher than the silica-based monolithic capillary column in the relevant research. The resolution of ethane and ethylene reaches 6.81 at 120 °C. The μGCC fabricated by ULAE method is composed of all-glass and has the uniform stationary phase coating because of the homogeneous microchannel surface which greatly improve the separation performance, resulting in a large resolution for methane and ethane. The all-glass μGCC has broad application prospects in light hydrocarbon separation. [Display omitted] • A novel all-glass based μGCC prepared by ULAE method. • The microchannels made by homogeneous material resulting continuous stationary phase coating. • Baseline separation of light hydrocarbons (C 1 –C 4) at 100 °C. • The resolution of methane and ethane can reach 12.98. [ABSTRACT FROM AUTHOR]

• The composite FG-HKUST-1 was used as a stationary phase for the μGCC. • The μGCC can effectively separate light hydrocarbon mixtures (C 1 -C 4) with a resolution of 9.2 for methane and ethane. • The difference in the retention time between methane and ethane was 1.11 min. • The retention factor of ethane and the resolution of methane and ethane were increased by 166 % and 114 %. A composite material was synthesized at room temperature by performing modification of the copper benzene-1,3,5-tricarboxylate (HKUST-1) metal-organic framework material by multilayer fluorinated graphene (FG). The FG-HKUST-1 composite was used as a stationary phase for a micro gas chromatography column (μGCC) fabricated using micro-electro-mechanical system (MEMS) technology. The separation results showed that the μGCC with the FG-HKUST-1 composite stationary phase achieved a baseline separation of C 1 -C 4 in 8 min. The retention factors for C 2 -C 4 were 2.13, 7.14, and 12.04, respectively. The maximum relative standard deviation (RSD) of the retention times was 0.14 %. The difference in the retention time between methane and ethane was 1.11 min, with a resolution of 9.2 for methane and ethane. The retention factor of ethane and the resolution of methane and ethane were increased by 166 % and 114 %. Therefore, this μGCC is promising for separating light hydrocarbons with widely differing concentrations. [ABSTRACT FROM AUTHOR]

A novel micro gas chromatography column (μGCC) with straight-sided elliptic microchannel cross sections was prepared by ultrafast laser-assisted chemical etching inside a glass substrate. The straight-sided elliptic cross sections resulted in a uniform distribution of the flow velocity field. This uniform distribution and the use of a microchannel with a consistent composition led to a uniform stationary phase coating. Upon the separation of a test mixture of C7–C11 alkanes, highly symmetrical chromatographic peaks were obtained. The tailing factors of the chromatographic peaks ranged from 0.95 to 1.05, which satisfies the relevant provisions of Pharmacopoeia of the People's Republic of China (ChP). The test results show that the improvement of the tailing factors is mainly due to the optimization of the cross-section structure rather than the optimization of the test conditions. Notably, due to the simple preparation processes and the low cost of the glass substrate, the total manufacturing cost of this novel μGCC is low. [Display omitted] • A novel μGCC was fabricated by ULAE inside the glass substrate. • The μGCC has straight-sided elliptic microchannel cross sections. • The μGCC has uniform stationary phase distribution with T f of 0.95–1.05. • The μGCC is suitable for high accuracy qualitative and quantitative analyses. [ABSTRACT FROM AUTHOR]