Analysis of MeHg in Biota by Cold Vapor Atomic Fluorescence Detection

Analysis of Methylmercury in Biota by Cold Vapor Atomic Fluorescence Detection with the Brooks-Rand “MERX” Automated Mercury Analytical System

The following standard operating procedure (SOP) is used by the U.S. Geological Survey’s Mercury Research Laboratory (MRL) to determine methylmercury (MeHg) concentrations in biota. This SOP describes the preparation of the sample and subsequent analysis. Biological sample is weighed into Teflon vials and digested in 4.5 M Nitric Acid at 60°C for 8 hours. Sample extract is added to reagent water in 42 ml glass vials, titrated with an equivalent volume of 5 M Potassium Hydroxide, and buffered with Sodium Acetate/Acetic Acid to a pH of 4.5 – 5.0. Sodium tetraethylborate (NaTEB) is added to the sample resulting in ethylation of the oxidized mercury species (Hg2+ and MeHg+ ). The volatile ethylated species, as well as elemental mercury, are purged from the sample with argon gas, retained on Tenex traps, thermally desorbed back into the sample stream, and separated by mass with a gas chromatography column. The elemental and ethylated mercury species are released from the column en masse into the sample stream, thermally oxidized to elemental mercury, and detected by cold vapor atomic fluorescent spectrometry (CVAFS). Sample analysis is conducted by the Brooks-Rand “MERX” automated mercury analytical system. Quality assurance and control protocols are employed throughout sample preparation and analysis, including: laboratory practices to prevent sample contamination, method and analytical blanks, sample replication, and analysis of certified reference materials (CRM).

Mercury Research Laboratory, 2016