Simultaneous determination of CFC-11, CFC-12, N2 and Ar in water

We have developed a new method for the simultaneous analysis of CFC-11, CFC-12, N-2, and Ar in water that allows field samples, collected in copper tubes and locked gas-tight, to be transported and stored for several weeks. In the laboratory the gases are extracted in a vacuum system and frozen onto cold traps. CFCs are measured with a GC-ECD, and N-2 and Ar are measured with a GC-TCD. Detection limits are 0.007 pmol kg(-1) for CFC-11, 0.017 pmol kg(-1) for CFC-12, and 0.89 mu mol kg(-1) for N-2 and Ar. The reproducibility of replicate samples with modern CFC concentrations (1 sigma) lies within +/-1.8% for CFC-11, +/-1.5% for CFC-12, +/-0.6% for N-2, and +/-0.8% for Ar. The oxygen demand and anoxic degradation rates of CFCs in the copper tube samplers were determined with lake water. At room temperature (22 degrees C), the oxygen demand is 14.3 +/- 7.6 mu mol kg(-1) d(-1), and the CFC-11 anoxic degradation rate is 0.0026 +/- 0.006 pmol kg(-1) d(-1). For CFC-12, no anoxic degradation was detected within 200 days.