Abstract: In this study, a micro-injector for portable gas chromatography （GC） systems is designed and fabricated based on micro-electro-mechanical system （MEMS） technology. The micro-injector features a four-layer composite structure composed of glass-polyimide （PI）-silicon-glass. The chip integrates four elastic membrane microvalves actuated by external pneumatic pressure, a central serpentine metering loop for quantitative sampling, and a series of microchannels that jointly control gas flow paths. The central serpentine metering loop is designed to achieve a fixed sampling volume, while the surrounding microchannels enable flexible flow switching under the coordinated control of the microvalves. The micro-injector operates through three working stages： sampling stage, injection stage, and purging stage. During the sampling stage, the microvalve connecting the sample gas source to the gas outlet is opened, allowing the sample gas to flow into the central serpentine metering loop. The gas fills the loop and reaches equilibrium, thereby completing quantitative sampling. During the injection stage, the microvalve connecting the sample gas to the outlet is closed, while the microvalve connecting compressed helium （He） to the chromatographic column is opened. The compressed helium acts as the carrier gas and drives the precisely metered sample gas from the serpentine loop into the analytical column. During the purging stage, the microvalve connecting the sample gas to the chromatographic column is closed, and the microvalve connecting compressed helium to the gas outlet is opened. The helium gas flushes the metering loop and removes any residual components, preparing the system for the next sampling cycle. The operating principle of the microvalves is based on pneumatic actuation of an internal elastic membrane. External pressure is applied to deform the membrane, causing it to alternately contact or separate from the silicon substrate, which is patterned with two independent gas channels. Through this contact or separation, the opening and closing of the microvalves are controlled. This microvalve design is structurally simple, highly effective, and cost-efficient, while providing reliable switching performance and low leakage. For device fabrication, deep reactive ion etching （DRIE） is employed to perform double-sided micromachining of the silicon substrate, forming the microvalves and microchannels. Laser micromachining is used to fabricate gas chambers and through-holes in the top glass layer for microvalve actuation, as well as gas inlet and outlet ports in the bottom glass layer for introducing and exhausting sample gas and carrier gas. The backside of the silicon substrate is hermetically sealed to the bottom glass layer via anodic bonding, ensuring high bonding strength and excellent sealing performance. The polyimide membrane is bonded to the top glass layer and the silicon substrate using customized double-sided adhesive, completing the sealed glass-polyimide-silicon-glass multilayer structure. Polyimide （PI） is selected as the deformable membrane material due to its excellent mechanical and thermal properties. The PI membrane exhibits a high tensile strength, enabling it to withstand long-term cyclic loading in microstructures. In addition, its outstanding thermal stability, with a long-term operating temperature range of 200-300 °C, makes it well suited for GC applications. The microvalves are controlled by external miniature solenoid valves and achieve a response time of 8 ms, satisfying the rapid response requirements of the micro-injector. The fabricated micro-injector has a compact size of 12.4 mm×12.4 mm ×1.4 mm and enables precise gas injection with a volume of 2.6 μL. The device exhibits low power consumption, small footprint, and chemically inert surfaces that reduce sample adsorption. Experimental results demonstrate excellent sealing performance with no leakage under high external pressure and good repeatability. Finally, the micro-injector is integrated into a portable gas chromatography system and applied to chromatographic analysis of carbon dioxide, methane, ethylene, and ethane. This study provides core component support for the development of miniaturized and high-precision portable gas chromatographs.

Key words: micro-injector, gas chromatography （GC）, micro-electro-mechanical systems （MEMS）, pneumatic microvalves