This is ideal for fixed gas-from-CO2 analysis where no "high boilers" are present. Column 1 is packed with a porous polymer and Column 2 with molecular sieve. The sample loop is loaded in Position A. When the valve is switched, the loop contents are sent onto Column 1.
As the inorganic gases and methane leave Column 1 and enter Column 2, the valve is returned to Position A, reversing the column sequence. CO2 now leaves Column 1, becoming the first peak. The inorganics and methane are separated by the mole sieve and pass through the porous polymer column to the detector.