A capillary-column Chromatographic system for efficient chlorofluorocarbon measurement in ocean waters

Abstract

We describe a new gas Chromatographic analytical system for the joint measurement of the chlorofluorocarbons CFC-11, CFC-12, and CFC-113 and of CCl4 in ocean waters. From measurements at sea and in the laboratory we find overall precisions for surface waters of ±0.6, 0.6, 1.5, and 2.4% and detection limits of 0.002, 0.002, 0.008, and 0.003 pmol/kg, for CFC-12, CFC-11, CFC-113, and CCl4, respectively (1-σ equivalents). The measurement repeat period is 17 min. A purge-and-trap approach, and other details, pay tribute to the work of Bullister and Weiss [1988]. A capillary column in combination with a low-volume trap yields higher resolution than reported for other systems. There is full separation of CFC-12 from N2O and a satisfactory one of CFC-113 from CH3I; to achieve the latter, a short packed column is operated in series with the main column. Slow purging of CCl4 from the water samples contributes to its analytical error. The system is fully automated, allowing eight water samples and associated calibration measurements to be carried out unattented. Water samples are transferred into the system by means of flow-through containers incorporating glass ampoules. Alternatively, the ampoules can be flame-sealed, allowing sample storage for later analysis ashore. The performance of the system is assessed in some detail to serve as reference information for other CFC measurement systems and to direct future system tuning and developments. The system has been successfully employed at sea repeatedly. Sections from cruise M30/2, 1994 (Atlantic, 48° N), are presented as an example.