A Miniaturised Gas Chromatographic Module on a Credit Card Sized Motherboard

摘要

Gas chromatography is a very efficient analysis tool, which is used in chemical laboratories since discovery in 1942. Complex organic substance mixtures can be separated in several minutes and quantitatively analysed. In some cases gas chromatography (GC) is the only possible analytical method to analyse complex volatile organic compounds (VOC). GC based analysis systems are not only used in laboratories, today they are also put into vehicles for field monitoring and analysis. The demand of small portable handheld GC systems is growing continuously. Miniaturised GC are faster and consume much less energy and carrier gas than classical bulk systems. With such systems autonomic operation on any place is possible for longer times. The opportunity of mobile operation will stimulate new applications and additional operation areas. The first micro machined GC analyser on a silicon wafer was published in 1979 by S.C. Terry of Stanford University but was no commercial success due to problems with the introduction of a homogeneous stationary phase. As miniaturised versions only injectors and thermal conductivity detectors are used in commercially available chromatography systems today (Varian and Agilent). The Technical University of Hamburg-Harburg had developed a new generation of miniaturised separation columns, micro thermal conductivity detectors (μTCD) and sample injectors. Noteworthy is the micro machined separation column with a plasma polymerised polydimethylsiloxane (PDMS) like layer, which is a standard stationary phase material. This layer is realised by plasma enhanced chemical vapour deposition (PECVD) of silicon organic materials on the column walls i.e. the trenches in a silicon wafer and on the corresponding areas of the glass lid.This technology allows the economic production of micro machined GC systems and thereby a drastically miniaturisation of such analysis systems. SLS MICRO TECHNOLOGY uses such technology to realise a miniaturised GC module with all GC components on a 80 mm by 50 mm sized board. This system is equipped with standard GC media connectors for probe inlet, probe outlet, carrier gas inlet and the exit of the μTCD to connect further detectors. The system also comprises heater elements for injector, detector and separation column. It offers very fast analysis times because the internal diameter of the separation column is only 60 μm, which is a common column diameter for high speed chromatography. The required polarity of the stationary phase depends on the analytical task. Therefore the polarity of the stationary phase can be adapted from polar to nonpolar. In such systems - as presented here - the carrier gas flow is less than 0.1 sccm which allows the miniaturised GC system to operate more than 12 weeks continuously from a 100 ml reservoir of carrier gas at 200 bar. The electrical power consumption of such system is less than 25 Watts. Already the first version of miniaturised GC modules delivers digital signals at the interface. The gas Chromatographic module presented in this paper will allow to build real portable analysis systems for field applications in the near future.