Dear Aa Amir thank you for your very interesting technical question. In this context please have a look at the following potentially relevant article which might help answering your question:
Metal and metalloid determination in biodiesel and bioethanol
This paper is freely available as public full text and can be downloaded as pdf file. It has been finally published in the Journal of Analytical Atomic Spectrometry:
Article Metal and metalloid determination in biodiesel and bioethanol