Abstract: A method includes receiving an x-ray signal transmitted from an x-ray transmitter through a coated separator membrane. The method also includes obtaining infrared (IR) signals from the coated separator membrane. The IR signals include two or more spectral components including peaks that include a first peak from the separator membrane. The method also includes the processor determining whether a second peak is present, and determining if at least one contaminant/additive exists in the coating present within the coated separator membrane. The method also includes calculating, by the processor, a concentration/area weight of the at least one contaminant/additive and a weight, density, or thickness of the coating.