A system and method of measuring volatile and semi-volatile reduced organic compound content and volatile and semi-volatile oxidized organic compound content in a sample, using a dual detection system is provided. The method comprises introducing the sample into a semi-permeable membrane introduction interface, sweeping permeate from the membrane introduction interface with a sweep gas, splitting the permeate into a first stream and a second stream, essentially simultaneously detecting volatile and semi-volatile reduced organic compounds and oxidized and semi-volatile organic compounds with a flame ionization detector and an electron capture detector, and computing differences in detector signals, thereby measuring volatile and semi-volatile reduced organic content and volatile and semi-volatile oxidized organic compound content in the sample.