Determination of anions and cations in biofuels

In order to control the quality of biofuels, such as biodiesel and bioethanol, ion chromatography (IC) is the method of choice. It is straightforward, fast and accurate and requires only moderate expenditures on instrumentation. Besides the quantitation of cations, glycerol and antioxidants in biodiesel, a direct-injection IC method allows the determination of the chloride and sulfate content in bioethanol according to the recent ASTM D 4806 standard. Traces of anions in a gasoline/ethanol blend such as E85 can accurately be determined in the sub-ppb range after Metrohm Inline Matrix Elimination using anion chromatography with conductivity detection after sequential suppression. While the analyte anions are retained on the preconcentration column, the interfering organic gasoline/bioethanol matrix is eliminated. Detrimental alkali metals and water-extractable alkaline earth metals in biodiesel are determined in the sub-ppm range using cation chromatography with direct conductivity detection applying automated extraction with nitric acid and subsequent Metrohm Inline Dialysis. Unlike high-molecular substances, ions in the high-ionic strength matrix diffuse through a membrane into the low-ionic water acceptor solution.

Metrohm AG

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