Sumari, S., A. Santoso, and M. R. Asrori. “A Review: Synthesis of Biodiesel from Low/Off Grade Crude Palm Oil on Pretreatment, Transesterification, and Characteristics”. Orbital: The Electronic Journal of Chemistry, Vol. 13, no. 4, Oct. 2021, pp. 385-91, https://periodicos.ufms.br/index.php/orbital/article/view/15585.