Estimation of mercury speciation in soil standard reference materials with different extraction methods by ion chromatography coupled with ICP-MS

Analytical methods for the speciation of mercury, based on microwave extraction and sonication extraction, have been tested to determine the inorganic mercury and methyl mercury contents in two standard soil reference materials: SRM 2710 Montana Soil and BCR 580 estuarine sediment. Prior to applying the speciation extraction methods, the mineral compositions were analyzed via XRD analysis, with SRM 2710 shown to be composed mostly of aluminum silicate minerals, while carbonate minerals were the major constituent in BCR 580. Two extraction methods, microwave and sonication, were tested for the analysis and recovery efficiency of total mercury. The accuracy and efficiency of each extraction method was also compared. In the analysis of total mercury, the microwave extraction method, with using methanol and HCl as extractants, was better for SRM2710, while the application of the sonication extraction method was more efficient for the calcite-based BCR 580. The results showed good separation and recovery efficiencies, with values reaching 100% of those estimated. The sonication method was selected for the speciation of mercury, especially in BCR 580. An extraction solution comprising of a 1:1 mixture of methanol and HCl was used for the sonication extraction of BCR 580, with the resulting extractants analyzed by IC-HG-ICP-MS for methyl mercury and inorganic mercury. As a simple, rapid, sensitive, and accurate method, sonication extraction was found to be satisfactory.