Simultaneous Determination of Chlorofluorocarbons and Sulfur Hexafluoride in Seawater Based on a Purge and Trap Gas Chromatographic System
Abstract Chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) are types of anthropogenic halogenated compounds, and are very important for ocean processes, including air-sea and water mass exchanges. Meanwhile, they can also be used to calculate some key physical and biogeochemical parameters such as the apparent oxygen utilization rate and anthropogenic CO2. Compared to CFCs, SF6 is quite difficult to measure in seawater due to its low solubility. However, it is useful to study the ocean processes based on both CFCs and SF6. In this study, a purge and trap gas chromatography system was developed to simultaneously measure CFC-12 and SF6 in seawater. The optimal conditions were as follows: trap temperature of −70 °C, purge time of 8 min, purge gas pressure of 310 kPa, desorption time of 30 s, desorption temperature of 90 °C. The method was simple and sensitive. The detection limit were 0.02 pmol kg−1 for CFC-12 and 0.03 fmol kg−1 for SF6. The analytical precision of CFC-12 was ±1.2% and that of SF6 was ±0.5%. The correlation coefficient (R2) values of all calibration curves were greater than 0.9995. This method was successfully used in the analysis of sea water samples collected during the 6th Chinese Arctic Research Expedition.