GB872259A - Improvements relating to gas chromatography - Google Patents

Abstract

<PICT:0872259/III/1> A gas chromatographic analyser comprises two contiguous compartments, one of which carries a valve for controlling the flow of carrier and sample gases, and the other of which contains a motor operating said valve to take a sample and direct it with the carrier gas through a column which is supported in heat conducting relationship on a wall of good thermal conductivity of the first-mentioned compartment. In the illustrated embodi <PICT:0872259/III/2> ment (Fig. 1), the column is in the form of a coil 14 wound on a mandrel 13 supported by a plate 12 which divides the apparatus into an upper and a lower portion. On the mandrel is supported a block 16 comprising the sensing and reference chambers 56, 57 (Fig. 3) of a thermal detector provided with thermistors 58, 59, and the various gas connections are made by co-operation of valve 15 which has milled slots 37, 38, 39 in its base. Carrier gas, e.g. helium, enters the base of the apparatus through line 41 and passes to the block 16 through flow regulator 20, flow restrictor 17 and preheater 43; sample gas enters the apparatus through line 48 and is passed through preheater 49 to the block 16. In the position shown in Fig. 3, sample gas is not being passed to the column but through a sample tube 47 to discharge 53. Meanwhile the carrier gas is passed through the column and the sensing and reference cells, (the latter being reached through valve 61 to reduce the pressure to atmospheric) and thence to outlet 55. On rotation of the valve the carrier gas is directed through sample tube 47 before being passed to the column thereby carrying the sample into the column, while sample gas passes directly to the outlet 53. The carrier gas in this case also flows through the reference cell 59 of the analyser. The preheater coils 43, 49 and the column 14 are maintained at the desired temperature by means of a 350 watt fast heater 22 in the wall of the mandrel controlled by a bimetallic thermostat in the bottom of the mandrel, and six heaters 24 controlled by a mercury thermostat in a slot in the side of the mandrel. A base heater may also be provided and a suitable circuit diagram for these heaters is shown. The valve 15 is operated by a motor 18 which is controlled by a switch operated in turn by a programmer as described and claimed in Specification 872,260 which also controls the electrical apparatus leading to a final result on a recorder. The apparatus may be programmed to provide bar graphs of the constituents of repetitive samples or a continuous recording of the sample gas in conventional form. The apparatus is enclosed in a housing, and the upper compartment in an explosion-proof cover.