Hello dgs. I would suggest ICP as a method to detect inorganic impurities. We did a lot of feedstock ICP detections when I was working with Ageratec and we came up over time with the following maximum values:
Ca 25, Mg 10, P 20, Cl 10, S 20 mg/kg. Many of the in the article critical inorganics are not represented here, since our focus was meeting the EN 14214 for the produced biodiesel, rather than inhibit complex formations. In that case the focus would have included Na, K, Al, Fe, Cu, Ni and Zn. Ok, the catalyst for biodiesel will have some Na or K, but it is good to be aware of any possible process disturbances before processing.