The Reston Groundwater Dating Laboratory

The SF5CF3 Lab Capabilities

The dissolved gases must be extracted from a minimum of 100 liters of water to measure ambient levels of SF5CF3 and CFC-13 in ground- and surface-water. Two glass bottles of gas are usually obtained from each extraction from ground waters.

Gas samples are collected in electropolished stainless steel cylinders using ultra-clean 12-volt portable pumps. Standard deviations of about 3 percent were routinely obtained for repeated measurements of standards. The calibrations were nearly linear within the measuring range. The analytical precision of the water analyses was about 20 percent near the detection limit of about 0.005 parts per trillion of SF5CF3 in 1970 air, and about 5 percent for ground water recharged after 1985.