We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22 m ATNFMopra Telescope located in Australia. The most commonly detected molecular lines are Nsub 2Hsup +, HNC, HNsup 13C, HCOsup +, Hsup 13COsup +, HCN, Csub 2H, HCsub 3N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. Total column densities of the different molecules, except Csub 2H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for Nsub 2Hsup + and HCOsup +. The Nsub 2Hsup +/HCOsup + and Nsub 2Hsup +/HNC abundance ratios act as chemical clocks, increasing with the evolution of the clumps.