  We provide a study of quantum chromodynamics with the technique of
Dyson-Schwinger equations in differential form. In this way, we are able to
approach the non-perturbative limit and recover, with some approximations, the
't Hooft limit of the theory. Quark mass in the propagator term goes off-shell
at low-energies signaling confinement. A condition for such occurrence in the
theory is provided.
