title: Determination of methylmercury in marine sediment samples: method validation and occurrence data.
abstract: The determination of methylmercury (MeHg) in sediment samples is a difficult task due to the extremely low MeHg/THg (total mercury) ratio and species interconversion. Here, we present the method validation of a cost-effective fit-for-purpose analytical procedure for the measurement of MeHg in sediments, which is based on aqueous phase ethylation, followed by purge and trap and hyphenated gas chromatography-pyrolysis-atomic fluorescence spectrometry (GC-Py-AFS) separation and detection. Four different extraction techniques, namely acid and alkaline leaching followed by solvent extraction and evaporation, microwave-assisted extraction with 2-mercaptoethanol, and acid leaching, solvent extraction and back extraction into sodium thiosulfate, were examined regarding their potential to selectively extract MeHg from estuarine sediment IAEA-405 certified reference material (CRM). The procedure based on acid leaching with HNO3/CuSO4, solvent extraction and back extraction into Na2S2O3 yielded the highest extraction recovery, i.e., 94±3% and offered the possibility to perform the extraction of a large number of samples in a short time, by eliminating the evaporation step. The artifact formation of MeHg was evaluated by high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS), using isotopically enriched Me(201)Hg and (202)Hg and it was found to be nonexistent. A full validation approach in line with ISO 17025 and Eurachem guidelines was followed. With this in mind, blanks, selectivity, working range (1-800 pg), linearity (0.9995), recovery (94-96%), repeatability (3%), intermediate precision (4%), limit of detection (0.45 pg) and limit of quantification (0.85 pg) were systematically assessed with CRM IAEA-405. The uncertainty budget was calculated and the major contribution to the combined uncertainty (16.24%, k=2) was found to arise from the uncertainty associated with recovery (74.1%). Demonstration of traceability of measurement results is also presented. The validated measurement procedure was applied to the determination of MeHg incurred in sediments from a highly polluted and scarcely studied area in the Caribbean region.
authors.affiliation: International Atomic Energy Agency, Department of Nuclear Sciences and Applications, Environment Laboratories, 4 Quai Antoine 1er, MC 98000, Monaco.
authors.forename: Luis
authors.initials: L
authors.lastname: Carrasco
authors.affiliation: International Atomic Energy Agency, Department of Nuclear Sciences and Applications, Environment Laboratories, 4 Quai Antoine 1er, MC 98000, Monaco. Electronic address: e.vasileva-veleva@iaea.org.
authors.forename: Emilia
authors.initials: E
authors.lastname: Vassileva
mesh_terms: D002849:Chromatography, Gas / Q000592:standards; D002851:Chromatography, High Pressure Liquid / Q000592:standards; D019015:Geologic Sediments / Q000737:chemistry*; D007553:Isotope Labeling; D013058:Mass Spectrometry / Q000592:standards; D008628:Mercury / Q000032:analysis / Q000302:isolation & purification / Q000592:standards; D008767:Methylmercury Compounds / Q000032:analysis* / Q000302:isolation & purification / Q000592:standards; D008872:Microwaves; D012015:Reference Standards; D013050:Spectrometry, Fluorescence / Q000592:standards; D013054:Spectrophotometry, Atomic / Q000592:standards
chemical_list: D008767:Methylmercury Compounds; D008628:Mercury
keywords: Gas chromatography–pyrolysis–atomic fluorescence spectrometry; Marine sediments; Methylmercury; Sample preparation; Traceability; Uncertainty; Validation