  nEXO is a proposed experiment that will search for neutrinoless double-beta
decay (0$\nu\beta\beta$) in 5-tonnes of liquid xenon (LXe), isotopically
enriched in $^{136}$Xe. A technique called Ba-tagging is being developed as a
potential future upgrade for nEXO to detect the $^{136}$Xe double-beta decay
daughter isotope, $^{136}$Ba. An efficient Ba-tagging technique has the
potential to boost nEXO's 0$\nu\beta\beta$ sensitivity by essentially
suppressing non-double-beta decay background events. A conceptual approach for
the extraction from the detector volume, trapping, and identification of a
single Ba ion from 5 tonnes of LXe is presented, along with initial results
from the commissioning of one of its subsystems, a quadrupole mass filter.
