Flame ionisation detection: (Flame ionisation phenomena)

Abstract

1,127,173. Flame ionization detectors. PYE Ltd. Feb.9, 1966 [Feb. 9, 1965], No. 5507/65. Heading G1N. A flame ionization detector, particularly for detecting organic gases or vapour present in the effluent from a gas chromatograph, has air cooled electrodes. In the embodiment, one electrode is constituted by a stainless steel burner cap 6, crimped onto an inlet pipe 5, electrical insulation being provided by a resin bonded fibre glass sleeve 8. The second electrode is constituted by a stainless steel cylinder 14, supported at its upper end in an outer stainless steel casing 1 by flanges 15 seated between two electrically insulating washers of PTFE 16, 17 and clamped in position by a ring 18. The carrier gas and organic gases or vapours are supplied to the detector through a connector 4 where they are mixed with hydrogen, entering through tube 27. The combined gases enter the device through an orifice 7 in the burner cap where the hydrogen is ignited by a glow plug 25 situated on a closure cap 24. Air is also supplied to the device at a slight pressure through a pipe 30, from whence it flows down the gap between the casing 1 and electrode 14, thereby cooling the electrode 14, round the flame, up through the electrode 14 and finally out through outlet 31 and pipe 32. The electrodes are connected by leads 9, 20 see also Fig. 4 (not shown), to a polarizing battery (37) in series with a D.C. amplifier (38), whose output is connected to an indicating and/or recording means (39), e.g. a conventional pen recorder. Two similar detectors can be connected into a similar circuit, Fig. 5 (not shown), having common hydrogen and air feeds, one being used as a reference. In this arrangement, the electrodes are oppositely polarized by means of a centre tapped polarizing battery (40). The detector may be mounted in the wall (33), Fig. 3 (not shown) of an oven (34), its lower end being in the oven which also houses a chromatograph column (35). One end of this column is coupled to the connector 4 and the other to a source of carrier gas and a sample injection chamber, through a connector (36).