Altering Capillary Gas Chromatography Systems Using Silicon Pneumatic Microvalves

Shimadzu Corporation researchers in Kyoto, Japan, tested new methods for separating components in capillary gas chromatography (GC) systems. Their findings were published in the Journal of Chromatography A (1).

gas chromatograph in a chemical laboratory, good daylight | Image Credit: © Александр Ивасенко - stock.adobe.com

In recent years, demands for simultaneous analysis of inorganic gases has been increasing. A significant driving force–that is, a force beyond conventional analysis of natural gas and refinery gases in the petroleum industry–has been a push towards decarbonization and carbon neutrality. It has been traditionally difficult for researchers to analyze samples containing both lower hydrocarbons and inorganic gases in parallel when using a single column. As such, multi-column gas chromatography (GC) using multiple columns with different retention properties was used for the mentioned samples.

Many conventional multi-column GC systems use two-position multi-port switching valves that simultaneously link half of the ports to switch the flow path to direct the target components to the appropriate columns for their separation and analysis. GC systems that use multi-port switching valves typically need to use more than one valve at once, which directly translates to more complex piping and large dead volumes. Subsequently, significant delays in valve switching can cause complicated timing adjustments; this requires substantial amounts of time for system assembly, adjustment, and tuning of different analysis conditions. To address these shortcomings, the scientists reported on a modular system that integrated and simplified complex piping connections by combining a channel plate with silicon pneumatic microvalves (Si microvalves) fabricated using semiconductor manufacturing technology. This system achieved significant reductions in assembly and adjustment time while simplifying system construction.

With this study, the scientists created a novel sampling and switching module by combining silicon pneumatic microvalves with a metal channel plate. This replaces the need for conventional two-position multiport switching valves to solve the problem of peak coelution in multi-column gas chromatography. The channel plate has a flow path volume equivalent to what one would find in a conventional capillary column. Further, the silicon microvalves developed in the study were characterized with minimal dead volume and high sealing performance.

By using Si microvalves, the scientists found it possible to seal target components within a capillary column alongside a mobile phase. In several experiments that utilize capillary columns, effects of diffusion on the sample bandwidth in the column were minimal during sealing; further, no deterioration of the peak shape was observed. In a multi-column GC system like natural gas analysis/refinery gas analysis (NGA/RGA), when multiple column separation systems are connected to a single detector, peaks can occasionally coelute.

To avoid peak coelution problems that are common in conventional NGA/RGA systems, one can customize the resistance or retention capacity of each column while carrying out adjustments in either the column temperature conditions or carrier gas flows. In contrast, when using Si microvalves, the scientists discovered it possible to control the timing of eluting components from each column by sealing any column and using a timed program for opening and closing valves. Further, using this approach to peak coelution could be avoided without making significant changes to the hardware or making alterations to analysis conditions, such as changes to column oven temperature or carrier gas flow rate. This can significantly simplify processes associated with setting up complex multi-column GC systems. Integrating complex piping flow paths into a flow path plate can also help with miniaturizing instruments.

Reference

(1) Shibamoto, S.; Lu, W.; Sato, A. Separation Method Using Column Sealing Technology with Silicon Pneumatic Microvalve in Capillary Gas Chromatography. J. Chromatogr. A 2025, 1751, 465950. DOI: 10.1016/j.chroma.2025.465950