Micro-Gas Chromatography Column Tested for Hydrocarbon Separation

A recent study led by scientists from the Chinese Academy of Sciences in Shanghai, China tested out a new type of micro gas chromatographic column (µGCC) for separating light hydrocarbons in micro gas chromatography (µGC) systems. Their findings were published in Analytica Chimica Acta (1).

Molecule structure. Science background with hydrocarbon molecules. 3d illustration. | Image Credit: © simone_n - stock.adobe.com

Gas chromatography (GC) uses several pieces of technology, including a gas chromatographic column (GCC). Traditional gas chromatograph systems must provide a temperate environment for the commercial CC, leading to large column ovens that increase overall volume and large power consumption. However, regular GC systems are non-conducive to portable and real-time monitoring. Namely, conventional GC systems have a typical peak power requirement of 2000–3000 V-ampere (2). This has led to scientists trying to reduce the size of the GCC, which can greatly reduce the volume of a GC system. The first major example of such a chromatography system can be found with the creation of a micro gas chromatographic column (µGCC) in 1979, with this system evolving throughout the years until the serpentine layout structure was created, which is believed to lead to the best performances for µGCCs.

A micro gas chromatography (µGC) system comprises multiple components, including a source of carrier gas, preconcentrator-injector, separation column, detector, pump, valves, and software for instrument control, data acquisition, and analysis. There has been an increased amount of marketability of portable GC instruments in recent years. These columns are developed in research and commercial laboratories. The most widely used type in µGC systems are polyimide-clad fused silica capillary tubing. Typically prepared using microelectromechanical systems (MEMS) technology, capillary columns carry with them several benefits; for example, for a given cross-sectional area, it can provide higher resolution due to homogeneous coating of stationary phase film along the length of the columns. Microcolumns also have advantages, such as enabling high speed and low power heating, lower manufacturing costs, and more. However, it is harder to use µGCCs for the separation of small molecule gas components, such as light hydrocarbons. Additionally, silicon glass bonding creates a heterogeneous microchannel surface, which can cause uneven stationary phase coating and prevent the improvement of separation performance.

In this study, the scientists proposed a novel all-glass based µGCC that is 2 m in length, with the goal of separating light hydrocarbons. The µGCC’s microchannels were directly prepared in a glass substrate using ultrafast laser assisted chemical etching (ULAE). The all-glass microchannels make the coating of the hydrophilic metal-organic frameworks (MOFs) stationary phase at a continuous rate, which is possible because of the homogeneous material composition. This led to a widely used copper based hydrophilic MOFs HKUST-1 being used as the stationary phase for coating and testing.

The results showed that the µGCC, which is classified as an open tubular column, can realize baseline separation of light hydrocarbons at 100 ºC. Additionally, the resolution of difficult separated compounds, methane and ethane, can reach 1298, which is 201.86% higher than the silica-based monolithic capillary column that is normally used in µGCC systems. As for the resolution of ethane and ethylene, it reached 6.81 at 120 ºC.

References

(1) Zhu, Y.; Xu, J.; Zhang, D.; Zhang, A.; et al. An All-Glass Based Micro Gas Chromatographic Column for Light Hydrocarbon Separation with HKUST-1 as Stationary Phase. Anal. Chim. Acta. 2024, 1287, 342057. DOI: 10.1016/j.aca.2023.342057

(2) Regmi, B. P.; Agah, M. Micro Gas Chromatography: An Overview of Critical Components and Their Integration. Anal. Chem. 2018, 90 (22), 13133–13150. DOI: 10.1021/acs.analchem.8b01461