GB890158A - Gas chromatograph - Google Patents

Abstract

A method of gas chromatography comprising <PICT:0890158/III/1> <PICT:0890158/III/2> injecting a sample mixture into a column, eluting said sample with a carrier gas and removing all sample components present in the effluent gas, is characterized in that the sample-free carrier gas is recycled to the column. To increase the resolution, the effluent, prior to removal of components, may be recycled through the column once or more. In a first embodiment (Fig. 1) of apparatus according to the invention, carrier gas is supplied from line 33 to a ballast tank 16 and passes into a column assembly 19 through a pressure regulator 17 and an inlet assembly 18, provided with heating means for the gas sample to be separated, which enters through line 42. The gases pass down the columns and are separated and passed through a sample chamber 29 of a detector cell 20. Carrier gas is conveyed to the reference chamber 28 of the detector cell through a by-pass line and thereafter returns to the main gas flow. The separated gases pass through a trapping manifold 60, whereby successive portions of the column effluent may be directed into different condensers 21, 22 for condensation of the various components. Said manifold may be operated manually having regard to the indication of recorder 66, or a valve control 73 actuated by the output of the detector cell may be provided. Clean-up traps are provided to remove any remaining condensable vapours before returning the carrier gas to the system. A pump 15 is provided to circulate the gases. If it is desired to increase the resolution of the apparatus, the effluent gas is not immediately passed through the condensers but first recycled through the column several times, by-pass lines 128 and 131 being provided for this purpose. In an alternative flow system (Fig. 11, not shown), the effluent from the column is divided and part passed through the sample chamber of the detector cell, whilst the remainder is passed through condensers as above. The carrier gas freed from condensable gases is also divided, part being recirculated and part being passed through the reference chamber of the detector cell. In the arrangement shown in Fig. 1, heat is supplied to the column assembly 19 by means of a heater 49, energized by a heat controller 50 actuated by a thermistor or other heat controlling element 51. Heat is similarly supplied to the inlet assembly 18 and to the detector cell 20. One form of inlet assembly in which a liquid sample is vaporized by passage through a helical channel is described in detail (Figs. 7-9, not shown, see Group XI). In one embodiment (Figs. 2-4, not shown), a column assembly comprises eight U-tubes located in a good thermally conductive material, such as aluminium, inlet and outlet headers being connected respectively to the ends of the U-tubes. In another embodiment, see Fig. 6, chromatographic columns 97, 98 are provided with a fixed manifold 95, having inlet and outlet conduits 96, 99, and a rotatable manifold 100, having pipes 102, 103, 104, whereby the columns may be connected in parallel or series.