The chemical stability of the binary metal oxide catalyst was
investigated by analyzing the presence of free metal content in the
biodiesel product which could be attributed to the occurrence of
leaching. The biodiesel product from the reusability test was
analyzed without further purification step by atomic absorption
spectrometer (AAS-S Series; Thermo Scientific, San Jose, CA). The
concentration of Ca content (ppm) in biodiesel produced was
detected.