The NBR 15556 standard of the Brazilian Association of Technical
Norms (ABNT) [11] uses a sample dilution of biodiesel with organic
solvents and determination of Na, K, Ca and Mg by flame atomic
absorption spectrometry (F AAS) in contrast to the European norm EN
14538, which recommends the use of the optical emission spectrometry
technique with inductively coupled plasma (ICP OES).