Abstract: A repetitive gas chromatograph employing a backflush valve downstream from the detector and a separate sample injection valve located upstream located directly upstream from the single chromatographic column. Each valve is operated independently of the other so as to allow flexibility in the timing of going into backflush operation and returning the sample valve immediately after sample injection onto the column to sample passage through the sample valve so as to more quickly establish equilibration of the sample and the sample valve's walls. Type and location of sample valve and backflush valve allow continuous monitoring of a sample stream.