Method for Purification of Krypton from Environmental Samples for Analysis of Radiokrypton Isotopes

摘要

Radiokrypton isotopes (~(81)Kr and ~(85)Kr) are ideal tracers and chronometers of various environmental processes. Atom trap trace analysis (ATTA) is capable of determining the ultralow isotopic abundances of radiokryptons (<10~(-12)) provided that 50 (mu)L of pure Kr is available. The analysis by using ATTA of ~(81)Kr in naturally occurring gases of interest, e.g., dissolved gases in hydrological reservoirs, requires separation of parts-per-million (ppm) level Kr from chemically airlike bulk gas. A newly developed Kr purification system is based on conventional cryogenic distillation and gas chromatography to which continuous monitoring of gas effluent composition using a quadrupole mass spectrometer brings significant advantages. Simple cryogenic distillation is controlled based on the evolution of N_(2)/Ar ratio that is relatively constant in naturally occurring, inorganic gas. Gas chromatographic separation of parts-per-million by volume (ppmv) level Kr from up to a few liters of bulk gas can be achieved by concentrating the Kr under the chromatographic tails of major components. The system described here is capable of extracting Kr of >98percent purity from 5-125 L STP (standard temperature and pressure) of bulk gas with >90percent yield within several hours. This system is generally useful for separation of microliter amounts of unreactive trace volatile compounds from large-volume gas samples.