  We determine the volume and mass dependence of scalar and pseudoscalar
two-point functions in N_f-flavour QCD, in the presence of an isospin chemical
potential and at fixed gauge-field topology. We obtain these results at second
order in the \epsilon-expansion of Chiral Perturbation Theory and evaluate all
relevant zero-mode group integrals analytically. The virtue of working with a
non-vanishing chemical potential is that it provides the correlation functions
with a dependence on both the chiral condensate, \Sigma, and the pion decay
constant, F, already at leading order. Our results may therefore be useful for
improving the determination of these constants from lattice QCD calculations.
As a side product, we rectify an earlier calculation of the O(\epsilon^2)
finite-volume correction to the decay constant appearing in the partition
function. We also compute a generalised partition function which is useful for
evaluating U(N_f) group integrals.
