Retention of Tritiated Alcohols by Zeolites Used in Indoor Air Sampling

Zeolite 4 Å, typically used in air samplers for indoor tritium monitoring, was tested for the uptake of organically bound tritium (OBT) compounds, in particular low-molecular-weight alcohol vapors. In a straightforward synthesis, tritiated methanol (CH₃OT, 1) and ethanol (CH₂CH₂OT, 2) were obtained from the hydrolysis of the respective alkoxides with tritiated water (aqueous HTO solution). In an independent approach, methyl-group tritiated methanol (CH₂TOH, 3) was produced via hydrolysis of [³H]-methyl-4-nitrobenzenesulfonate. Blank experiments for the tritium exchange on hydrated glass surfaces were conducted. Tritium losses were found negligible under ambient conditions. These tritiated alcohols were applied in batch experiments to test the sorption of their vapor onto zeolite 4 Å. After 24 h of exposure of the zeolite to the alcohol vapor, sorbed tritium compounds were desorbed by leaching with H₂O and quantified by liquid scintillation counting. At room temperature (22 °C), the sorption of tritiated alcohol vapor by the zeolite (as quantified via the recovery of activity in the leachate) is nearly quantitative. At elevated temperature (60 °C), the activity recovery decreases down to 62-75%. By contrast, the zeolite loading of sorbed alcohols (as expressed by mass of sorbed alcohol per mass of zeolite) increases with the same temperature increase from 20.3 ± 2.0 mg g^-1 to 30.9 ± 2.8 mg g^-1 for 1; from 10.7 ± 1.0 mg g^-1 to 31.0 ± 2.6 mg g^-1 for 2; and from 12.1 ± 2.1 mg g^-1 to 34.7 ± 2.0 mg g^-1 for 3. Under the simulated environmental conditions, zeolite 4 Å shows sufficient affinity toward dilute tritiated methanol and ethanol to be considered useful for indoor air monitoring.