In-Situ Monitoring of Gas Molecules in Chromatography by Utilizing a Pressure Sensor

We report a novel concept and testing results of utilizing a pressure sensor as an in-situ gas sensor for a micro gas chromatography system. The pressure sensor utilized a phenomenon that instant viscosity variation by an injection of gas molecules into a background gas stream caused instant pressure transient thus making it feasible to the in-situ monitor gas molecules using a pressure sensor during gas chromatography operation. Such a concept of viscosity-to-pressure conversion was experimentally proven and implemented. The implemented pressure sensors at multiple locations successfully monitored the progress of gas molecules in separation in four serially connected micro columns. This pressure sensor based chromatogram generated 125.5 Pa of pressure for $0.5\ \mu\mathrm{L}$ of hexane sample and showed a separation of hexane and heptane mixture with plate numbers of 93.68 and 244.69 respectively and with a separation distance and resolution of 30.5 and 2.4 respectively. The separation distance and resolution were 0.86 and 1.45 times to that of in FID separation, indicating no significant pressure sensor influences on separation.