Determination of sodium, potassium, calcium and magnesium cations in biodiesel by ion chromatography.

This work reports an ion chromatographic (IC) method for the quantitative determination of inorganic cations (Na(+), K(+), Mg(2+) and Ca(2+)) in biodiesel samples that were synthesized from different vegetable oils and fat. The proposed method uses water extraction, heating and ultrasound. The limits of detection (LOD) for each ion, in milligrams of the analyte per kilogram of biodiesel (mgkg(-1)), were respectively: 0.11 (Na(+)); 0.42 (K(+)); 0.23 (Ca(2+)); and 0.36 (Mg(2+)). The accuracy of the method was studied through recovery tests. For comparison, two samples were also analyzed using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) procedure. The paired Student t test and the Snedecor F test showed that both methods offer equivalent results in terms of accuracy and precision. The operational simplicity, accuracy and precision of the proposed method suggest that it can be a good alternative for the determination of inorganic cations in biodiesel samples.