Hi, different chemicals have different molecular structures and wights. Molarity is count per mole of the chemical compound. One mole of agent may have 15 atoms, another 150, so the detection of such chemicals is different. If the gas chromatograph has UV detector, then area under the peak will be different for the same molarities. In principle the higher molecular weight of the compounds, than higher peak under the same molarity. This of course depends on that what absorbs UV light in your compounds. You need to prepare standard curves of A and B, independently in order to quantify your compounds after peaks integration in the mixture.