The monitoring of sodium and potassium in biodiesel is necessary
because their hydroxides are employed as catalysts in its production.
These elements may be present as abrasive solids and insoluble soaps,
which can contribute to the damage and corrosion of engine parts
(injector, fuel pump, pistons, rings, etc.) eventually affecting its
performance [8].
The residual catalyst must then be removed from the
biodiesel through successive washes with water.
According to the
current Brazilian legislation [9], the maximum concentration of
sodium plus potassium in biodiesel is 5 mg kg−1.