Low-Temperature Oxygen Trap for Maintaining Strict Anoxic Conditions

A low-temperature $O_2$ trap was designed in order to achieve strict anoxic conditions. The work was motivated by observation of slow oxidation of $\mathrm{Fe}\left(\mathrm{II}\right)$ in an anaerobic chamber, leading to an estimated $3.8\times {10}^{-7}\mathrm{atm}$ $O_2$ (well below the $O_2$ monitor detection limit) despite recirculation of the $N_2:H_2$ atmosphere across a $\mathrm{Pd}$ catalyst. Very low $O_2$ activity inside an “anaerobic” chamber can result in erroneous conclusions regarding oxidation-reduction reactivities in anoxic environments. The $O_2$ trap consisted of two sequential barrier suspensions with $93.2\mathrm{mM}$ $\mathrm{Fe}\left(\mathrm{III}\right)$ as ferric hydroxide, $0.90\mathrm{mM}$ ${\mathrm{FeCl}}_2$, and pH 8.1. The partial pressure of $O_2$ was estimated to be less than $7.5\times {10}^{-9}\mathrm{atm}{O}_2$ when reactors were attached to the traps, based on no observed oxidation of $\mathrm{Fe}\left(\mathrm{II}\right)$.