Validation of method for the determination of mercury in the auxiliary substances azorubine 21% and azorubine 85% using cold-vapor atomic absorption spectrometry

Abstract

Heavy metals, such as mercury (Hg), sometimes can be found in auxiliary substances intended for pharmaceuticals use. Although the concentration of those elements is very low, their control isvery important because of its toxicity. Permissible concentration of mercury (Hg) in Azorubine 21% and Azorubine 85% is prescribed by the Directive of the European Commission concerning the specific purity criteria on food coloring. The  focus of this paper is on validating reliable methods of  Hg determination in auxiliary substances mentioned above, by Cold-vapor Atomic Absorption Spectrometry after microwave acid digestion of solid samples. To obtain possibly present Hg in Azorubine by conversion to  Hg²⁺ ions, samples were treated with a mixture of 1 mL MQ water + 1 mL 65% HNO₃ + 1 mL 70% HClO₄ + 5 mL 96% H₂SO₄ and heated by microwave for 30 min. on 1000 W in sealed TFM^TM – PTFEtubes. The resulting solutions are diluted and analyzed for Hg using cold vapor atomic absorption spectrometry with sodium borohydride as a reducing agent. The method was successfully validated and can be applied for the determination of Hg in solid samples of Azorubine 21% and Azorubine 85%, with value of recovery factor of 95% to 104% and 96% to 105%, respectively.