Dual column gas chromatograph and method for analysis

摘要

A process for analysing a sample by gas chromatography uses a first and a second column in conjunction with a carrier gas inlet, a detector and a vent line, and includes the steps of: directing the flow of carrier gas through the first column, the second column and the detector in that sequence, and then injecting a sample into the stream of carrier gas ahead of the first column and continuing passing the carrier gas until the lower boiling constituents of the sample have been eluted from the first column and have entered the second column, and then changing the pattern of flow so that the carrier gas is directed through the first and second columns and the detector in a different sequence and optionally different direction, the flow through the detector occurring after the flow through at least one of the columns. A modification of the process includes the use of two detectors and a further switch valve. The change of flow pattern is effected in an apparatus comprising a valve having a body provided with six ports for connecting the various elements of the device including inter alia two columns and a detector or detectors, combined with co-operating movable, e.g. rotary, member having six ports coupled in pairs by passages, the ports in the two members being angularly so spaced that in each position of adjustment the ports of the two members will register with each other. The invention is described with reference to diagrams which also show the use of a six port valve adapted for use as a constant volume sampling valve.