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Construction of a Leak-Inlet System for the LKB 9000 Gas ChromatographMass Spectrometer

Volume 24, Number 5 (Oct. 1970) Page 543-544

Hawk, Robert E.; Jennings, Ralph W.

Apart from the direct inlet system which permits the introduction of substances with very low volatility and/or thermal stability into the mass spectrometer, the LKB instrument also permits the high speed recording of mass spectra of volatile compounds as single components or components of mixtures eluted from a gas chromatograph. Caution must be exercised in the interpretation of these spectra in view of posible peak or component overlap using the gas chromatographic column. At times it is useful to have another alternative system for the rapid introduction of controlled amounts of gaseous substances and/or highly volatile liquids and solids as well as reference samples such as the perfluoroalkanes directly into the ion source of the mass spectrometer for analysis. A heated molecular leak system for this purpose was developed (see Fig. 1). An inexpensive leak-inlet system which is satisfactory for the highly volatile and reference substances can be easily constructed, and thereby greatly increases the versatility of the instrument. The sample introduction tube is an 8 mm (5/16 in.) o.d. stainless steel tube inserted into the analyzer tube in the same way as a direct probe. The tube is flared at one end and attached to a Manostat flow controller, 78-425-01, or similar valve. An inner Teflon tube, 3/16 in. o.d. × 1 mm i.d., and a 3/16 in. Teflon ferrule in the flared end of the steel tube afford a chemically inert pathway and the flow restriction necessary for sensitive control at low pressures. A standard 8 mm o.d. Manostat glass joint into which has been inserted a silicone rubber plug septum (the same as that used by LKB's GC column) comprises the sample reservoir. For samples of low volatility, the glass inlet can be heated by an aluminum block containing a cartridge heater (Fig. 2).