Fully automated spectrophotometric procedure for simultaneous determination of calcium and magnesium in biodiesel

• First spectrophotometric determination of calcium and magnesium in biodiesel.
• Simultaneous determination was achieved with a simple on-line dilution of the sample.
• Possibility of high-throughput analyses.
• Fully automated method.
• Analytical signal does not depend on the type of biofuel.

An easily performed stepwise injection (SWIA) procedure based on on-line dilution of biodiesel samples and the formation of color-forming calcium (II) and magnesium (II) complexes with Eriochrome Black T (EBT) in an organic medium followed by spectrophotometric determination is presented. A sample of biodiesel was placed at the bottom of a mixing chamber connected to an automatic SWIA manifold. Isopropyl alcohol was used as the diluent under bubbling. The solution was submitted for on-line spectrophotometric simultaneous determination of calcium and magnesium based on the classic least-square method. The linear ranges were from 2 to 20 μg g−1 and from 1.2 to 12 μg g−1, and the detection limits, calculated as 3 s for a blank test (n=5), were found to be 0.6 μg g−1 for calcium and 0.4 μg g−1 for magnesium. The sample throughput was 30 h−1. The method was successfully applied to the analysis of biodiesel samples.

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