A free fatty acid is a carboxylic acid that is usually derived from a triglyceride or a phospholipid. Fatty acids can be saturated or unsaturated. The amount of free fatty acid in the feedstock impacts the biodiesel production process. Feedstocks that have a high percentage of free fatty acids typically undergo an acidesterification step prior to the more common trans-esterification process. The amount of free fatty acid in the sample is quantitated by titration with sodium hydroxide and the endpoint is determined potentiometrically (so that the measurement is not based on an observance of a color change). This analysis may also support RINS validation by assuring qualified feedstocks are directed to approved RFS2 pathways.