In this paper a methodology to connect the sensitivity of porphyrins coated quartz microbalances and the porphyrin molecular structure is outlined. Porphyrins can interact with guest molecules with different mechanisms exceding those usually considered in simple partition systems, For this reason in this paper an approach in the frame of the Quantitative Structure Activity Relationship models is proposed. Experiments here illustrated were concerned with an array of porphyrins based sensors differing only for the metal ion. Results show that different metals tend to capture distint physical descriptors of the guest molecule. In particular the set of analyzed porphyrins can be divided in those enhancing the sensitivity to electron donor molecules, electric dipole and molecular size.