  By analyzing the calculated baryon number susceptibility ratios
${\chi_{1}^{B}}/{\chi_{2}^{B}}$ and ${\chi_{3}^{B}}/{\chi_{1}^{B}}$ in
two-flavor system via the Dyson-Schwinger equation approach of QCD, we
determine the chemical freeze-out temperature and baryon chemical potential in
cases of both thermodynamic limit and finite size. We calculate the
center-of-mass energy dependence of the ${\chi_{4}^{B}}/{\chi_{2}^{B}}\,
(\kappa \sigma^{2})$ at the freeze-out line and find an excellent agreement
with experimental data when taking into account the finite size effect. Our
calculations indicate that the $\kappa \sigma^{2}$ exhibits a nonmonotonic
behavior in lower collision energy region. We also predict that the collision
energy dependence of ${\chi_{6}^{B}}/{\chi_{2}^{B}}$ is nonmonotonic.
