Refinery feedstocks can be characterized based on any of: dissociation of acids in the crude, breakup of naphthenic acid molecular associations, mass changes of samples, and / or dissociation of sulfur compounds in the feedstocks. The characterization is performed as a function of temperature via any of electrical resistivity measurement, crystal microbalance measurements of weight changes, vibrational spectroscopic analysis, voltammetry, electrochemical impedance spectroscopy (EIS) and combinations thereof. The method can be practiced in any of refinery, terminal, and laboratories. It can be used in conjunction with a system comprising models and hardware to optimize the usage of refinery feedstocks in the blending and valuation of the feedstocks. The system can be employed in any of refinery, terminal, and laboratories. In one embodiment, the characterization of refinery feedstocks is via the use of EIS.