  Observations of neutrino oscillations show that neutrinos have mass. However,
the best constraints on this mass currently come from cosmology, via
measurements of the cosmic microwave background and large scale structure. In
this paper, we explore the prospects for using low-frequency radio observations
of the redshifted 21 cm signal from the epoch of reionization to further
constrain neutrino masses. We use the Fisher matrix formalism to compare future
galaxy surveys and 21 cm experiments. We show that by pushing to smaller scales
and probing a considerably larger volume 21 cm experiments can provide stronger
constraints on neutrino masses than even very large galaxy surveys. Finally, we
consider the possibility of going beyond measurements of the total neutrino
mass to constraining the mass hierarchies. For a futuristic, 21 cm experiment
we show that individual neutrino masses could be measured separately from the
total neutrino mass.
