A multifunction flow channel switching module for multi-column capillary gas chromatography using silicon pneumatic microvalves

Abstract

Decades ago, multi-column GC was developed for separating analytes which cannot be separated with a single column by switching the flow channels and introducing them into multiple columns. Formerly, a channel switching system consisted of stainless-tube-type packed columns and multi-port switching valves which were connected by stainless-steel pipes. These systems utilizing packed columns are still widely used today, mainly for gas analysis, especially for refinery gas analysis and natural gas analysis related to oil refining. However, there have been no new development updates in terms of hardware for decades. Since multi-port switching valves are used, there are problems such as the high frequency of valve replacements due to wear of seals, high running costs as well as long downtimes. In recent years, a heart-cutting multidimensional capillary GC using pressure switching devices such as the Deans switch has been put into practical use. Compared to the switching valves, the pressure switching devices have no wearing parts and are maintenance-free. Multi-dimensional capillary GC using the pressure-switching method cannot be applied to the analysis of low-boiling-point gasses because the retention capacity of the capillary column is low and the column inlet pressure is far from the optimum value for switching. Because of this another related factors, it has not been able to completely replace the traditional methods. In this study, an ON/OFF type silicon pneumatic microvalve was designed and fabricated by semiconductor manufacturing technology, and a flow channel switching module was developed by mounting microvalves on a metallic channel plate which is made by diffusion bonding. The flow channel switching module using silicon pneumatic microvalves has a heat resistance of up to 310 °C, can withstand pressures up to 1.5 MPA or more, and a durability that can withstand over 2 million opening and closing operations. In addition, the reproducibility of the gas sample analysis showed good reproducibility values of RSD 0.1% or less for peak areas and RSD 0.01 to 0.04% for retention time. Flow path switching without the use of pressure switching simplifies method development in several ways. For instance, by incorporating the use of valves that can be opened and closed independently, it was possible to integrate several methods such as heart cut, precut, column switching, and backflushing flow path layouts.