Sample preparation of large mass black shale samples using ammonium bifluoride for instrumental analysis by ms/aes-icp methods

The technique of acid decomposition of 1000 mg black shale samples in an open system has been developed. The procedure involves the destruction of the mineral matrix with a fivefold excess of ammonium bifluoride at 230°C for 6 h, followed by the reagent removal through distillation and the subsequent treatment of the residue with a mixture of perchloric and nitric acids to achieve the complete dissolution. The resulting solution remains stable over time and serves as the basis for the direct determination of more than 60 elements using a combination of ICP–MS and ICP–AES techniques. The method enables the quantification of gold, silver, and rhodium directly in the post-decomposition solution with the computational correction of spectral interferences. The method was tested on reference black shale materials from the Baikal–Vitim province SLg-1 and SChS-1 (Sukhoi Log deposit, Irkutsk region, Russia). The study also presents analytical results for their updated counterparts, SLg-1A and SChS-1A.