The Gas Chromatograph Mass Spectrometer (GCMS) was an instrument
            carried on board the Viking Lander 1 spacecraft. It performed a
            molecular analysis experiment by searching for chemical compounds
            in the upper surface layer of Mars and measuring atmospheric
            composition near the surface. GCMS had high sensitivity, high
            structural specificity, and broad applicability to a wide range of
            compounds. Substances were vaporized from the surface material by
            a heating process while CO2 (labeled with C-13) swept through. The
            material was then carried into a Tenax gas-chromatographic column
            that was swept with hydrogen as a carrier gas. While passing
            through the column, substances were separated by different degrees
            of retention. The residual stream moved into the mass spectrometer
            (after hydrogen was removed by hydrogen-only-permeable palladium),
            and a mass spectrum (masses from 12 to 200 micron) was obtained
            every 10 seconds for the 84 minutes of the gas chromatogram. In
            some cases, the same sample was reheated at a higher temperature
            and analyzed to detect less volatile materials. For atmospheric
            measurements, gases were directly introduced into the mass
            spectrometer, bypassing the gas chromatograph column.

			This description was provided by the NASA Space Science Data 
			Coordinated Archive (NSSDCA).