Methodology for Hg determination in honey using cloud point extraction and cold vapour-inductively coupled plasma optical emission spectrometry

Abstract

This paper describes the development of a method for the determination of mercury in honey. Analyte pre-concentration/matrix separation is carried out by cloud point extraction (CPE), while cold vapour-optical emission spectrometry (CV-ICP OES) is used to detect the analyte. A careful analytical work was carried out in order to evaluate precision and accuracy of the method. Mercury was complexed with ammonium diethyldithiophosphate (DDTP) and Triton X-114 was used as surfactant. Parameters such as type and concentration of acid (HCl or HNO₃ + KCl), concentrations of complexant, surfactant and reductant (NaBH₄), dilution of the surfactant-rich phase and the mass of honey were evaluated. Two procedures of sample preparation were investigated: sonication in presence of L-cysteine and acid decomposition in closed vessel. Sonication was very effective for extraction of inorganic mercury (Hg²⁺), but it was observed the sample should be decomposed to ensure the quantification of total mercury. Certified dog fish liver, analyte recovery and comparison with an independent technique (cold vapour-inductively coupled plasma mass spectrometry) were used to evaluate the method. Analyte recovery close to 100% was observed when up to 2.0 g of honey were subjected to sonication or up to 1.0 g of honey was decomposed with acid. The enrichment factor (EF) obtained was 13 and the limit of detection (LOD) was 2.2 ng g⁻¹. The Hg concentration in the analyzed samples was lower than the LOD.