The biodiesel may contain materials that are in the form of abrasive solids, soluble metallic soaps, and unremoved reaction catalysts. The Sulfated Ash determination indicates gross levels of ash-forming compounds in the biodiesel. The primary ash-forming materials that may be present in biodiesel are calcium, magnesium, sodium, and potassium. Sulfated ash is determined in accordance with ASTM D874.
ASTM D6751 Requirement: a maximum sulfated ash content of 0.020% by mass.