A gas sampling device containing 200g of the sorbent Tenax is used to collect organic impurities from air that may be contaminated with 1,1,2-trichloro-1,2,2-trifluoroethane. At the end of sampling, 240 L of air had been drawn through the sampling system, and the concentration of the chlorofluorocarbon in the Tenax was 811 mg/kg. Assuming 100% trapping efficiency because no weight gain was observed in a second Tenax tube placed in series after the first, what was the contaminant concentration in the air in ppm? The ambient temperature was 18 degrees C and pressure was 750 mm Hg.