Patent GB-1435284-A (GB)
Title: Vapour-detection apparatus
IPC: G01N27/64
Filed: 1974-09-26
Abstract: 1435284 Vapour-detection apparatus MARSLAND ENG Ltd 26 Sept 1974 [1 Oct 1973 24 May 1974] 41842/74 Headings G1B and G1N An apparatus for detecting a specific vapour in an atmospheric sample comprises a collector assembly having an inlet and an outlet and a passage extending between the inlet and outlet, said passage being filled with a solid adsorbent which is capable of adsorbing the specific vapour together with other vapours in the sample and which can be readily heated to desorb the vapours, heating means for heating the adsorbent, a postition column connectable to the outlet of the passage for separating the desorbed vapours and a detector connected to the partition column for detecting the specific vapour, the inlet of the passage being connectable to a carrier gas source to provide a flow of carrier gas so that the carrier gas passes the desorbed vapours to the partition column for separation and the separated vapours to the detector for detection of the specific vapour, the assembly being movable between a sampling position where said passage is connected with the atmosphere whilst disconnected from the partition column and the carrier gas source, and an analyzing position where said passage is connected to the partition column and the carrier gas source while disconnected from the atmosphere, the apparatus also comprising means to draw the atmospheric sample over the adsorbent when the collector assembly is in the sampling position. There may be provided an additional passage to communicate the carrier gas source and the partition column. When the assembly is in the sampling position and to be disconnected therefrom when the assembly is in the analysis position. The detector preferably comprises a chamber having an inlet and an outlet for flow of the separated vapours therethrough, means to provide free electrons in the chamber, and a cathode and an anode in the chamber for connection to means to apply a D.C. voltage to the electrodes and means to monitor the current flowing between the electrodes. The adsorbent is preferably gold wire or nickel wire. The carrier gas is preferably helium or argon, or argon containing about 5% by volume of methane. An apparatus of the type described above is shown in Figs. 2 and 3. In Fig. 2, the collector assembly is shown in the sampling position. A probe 10 which may be a steel tube lined with a P.T.F.E. tubing is attached to the front plate assembly 11 and is provided with a carrier gas inlet 14. The collector 18 is positioned in a sliding block assembly 3, 4, 5 which may be manually moved from sampling to analyzing position. An additional or reference passageway is provided in the sliding block assembly. The collector 18 is in the form of a wire coil inserted in a P.T.F.E. tubing, the ends of the coil being connected to collector heating circuit 24 Fig. 1 (not shown). Collector 18 is connected with back plate assembly 17, and in the sampling position, this connection communicates collector 18 with right-angled passage 27 which is connected to a pump 28 (not shown). When the sliding block assembly is moved to the analyzing position, collector 18 communicates via tubing 30 with partition column 8, which column communicates with detector chamber 9. In chamber 9, there is provided a radio-active foil 43, which also serves as a cathode, and a rod 44, which functions as an anode. The applied D.C. voltage may be either continuous or pulsatory. When the carrier gas alone passes through the assembly, a standing current is generated. When certain compounds are present in the carrier gas, a decrease in standing current is observed. The output of the detector is preferably processed by a signal processing circuit which takes the second derivative of the output signal.