Environmental Analysis Monitoring Copper in Fuel ethanol by Anodic Stripping Voltammetry
The presence of copper in fuel ethanol blends can negatively affect engine performance. Thus, the US ASTM D 4806 and the European prEN 15376 both restrict the amount of copper in fuel ethanol to 10 µg/L. Anodic stripping voltammetry (ASV) is the determination method of choice, as it allows the quantification of Cu(II) without any sample pretreatment. The presence of heavy metal traces in car fuels has an adverse effect on engine performance. Copper, for example, is a very active catalyst for the low-temperature oxidation of hydrocarbons. Consequently, copper concentrations above 12 µg/kg in commercial gasoline are expected to promote the deterioration of olefins and the formation of gum. In order to monitor heavy metal traces, anodic stripping voltammetry (ASV) is the method of choice. ASV is a sensitive and selective electroanalytical technique comprising two steps. Firstly, metal ions are electrodeposited on the mercury electrode, which is held at a suitable potential. Secondly, the (amalgamated) metal deposits are anodically stripped from the mercury electrode by scanning the potential. The ASV is performed using the hanging mercury drop electrode (HMDE) and the Metrohm 797 VA Computrace for trace analysis. The HMDE is used with a platinum auxiliary electrode and an Ag/AgCI reference electrode using saturated lithium chloride in ethanol as the inner electrolyte. The concentration of the copper in the samples is quantified by standard addition.
Reader Reply Card no 32
Ion Chromatographic Determination of Anions and Cations in Biofuels
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Intelligent Ion Chromatography IC for Professionals
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. Biofuel quality can be severely impaired by the presence of ions that lead to corrosion in the vehicle components and cause salt deposits clogging filters and fuel injector nozzles. Therefore, standards defining quality specifications and test methods have been developed. In this context ion chromatography plays a crucial role. 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 pre- concentration 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.
Reader Reply Card no 33 Reader Reply Card no 34 AET October/November 2008
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Ion analysis
Ecknauer+Schoch ASW
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