The quark number susceptibility is expressed as an integral in terms of dressed quark propagator and dressed vector vertex. It is then investigated with the latter two- and three-point functions confronted with a Dyson-Schwinger equation model which accommodates both finite temperature and baryon chemical potential. The critical end point in the phase diagram is identified and the behavior of the quark number susceptibility around the critical end point is highlighted. The characteristic features found agree well with recent lattice QCD simulation results.

14 pages, 4 figures, revtex4, A discussion on the sensitivity of the results with respect to the variation of parameters and a new figure added