  Based on the previous work in [Y. Jiang, Y.M. Shi, H.T. Feng, W.M. Sun and
H.S. Zong, Phys. Rev. C {\bf 78}, 025214 (2008)] on the quark-meson vertex and
pion properties at finite quark chemical potential, we provide an analytical
analysis of the weak decay constant of the pion ($f_\pi[\mu]$) and the pion
mass ($m_\pi[\mu]$) at finite quark chemical potential using the model quark
propagator proposed in [R. Alkofer, W. Detmold, C.S. Fischer and P. Maris,
Phys. Rev. D {\bf 70}, 014014 (2004)]. It is found that when $\mu$ is below a
threshold value $\mu_0$ (which equals $0.350 \mathrm{GeV}$, $0.377
\mathrm{GeV}$ and $0.341 \mathrm{GeV}$, for the $\mathrm{2CC}$,
$\mathrm{1R1CC}$ and $\mathrm{3R}$ parametrizations of the model quark
propagator, respectively.), $f_\pi[\mu]$ and $m_\pi[\mu]$ are kept unchanged
from their vacuum values. The value of $\mu_0$ is intimately connected with the
pole distribution of the model quark propagator and is found to coincide with
the threshold value below which the quark-number density vanishes identically.
Numerical calculations show that when $\mu$ becomes larger than $\mu_0$,
$f_\pi[\mu]$ exhibits a sharp decrease whereas $m_\pi[\mu]$ exhibits a sharp
increase. A comparison is given between the results obtained in this paper and
those obtained in previous literatures.
