Description
The method is applicable to all biological materials, except possibly oils. The method has been tested in an interlaboratory methods performance study for magnesium from concentrations of 250 mg/kg of dry sample and for calcium from concentrations of 250 mg/kg of dry sample. Note that a high residual concentration of nitrate ions interferes with the determination of calcium. Concentrated nitric acid and hydrogen peroxide are added to the weighed sample. The sample is digested in a microwave oven. Any commercially available microwave oven for laboratory use may be used. In this method the CEM microwave oven is used as an example. Lanthanum(III)oxide is added to standards and sample solutions to prevent interference from phosphate ions. The concentrations of magnesium and calcium are determined using flame atomic absorption. The concentrations of the elements are calculated using standard curves.
The collaborative study is published in Journal of AOAC INTERNATIONAL, Volume 81, Issue 6, 1 November 1998, Pages 1202–1208, https://doi.org/10.1093/jaoac/81.6.1202.
According to the collaborative study the method best suited for matrices >3830 mg/kg Ca due to an observed low precision for matrices with 254-839 mg/kg (HORRAT >2, RSDR 15-23%).