Rapid determination of femtomolar methylmercury in seawater using automated GC-AFS method: Optimisation of the extraction step and method validation.

Among ionic mercury species methyl mercury (MMHg) is the most toxic form present in the environment, which is known to be bio-accumulative neurotoxin in the aquatic food chain and could provide the major route of exposure for humans to mercury through consumption of marine food products. The availability of reliable analytical methods for evaluating spatial and temporal contamination trends of MMHg in the ocean is an important prerequisite for marine monitoring. Sound strategies for marine monitoring call also for measurement systems capable of producing comparable analytical results with demonstrated quality. A sensitive analytical procedure for environmental monitoring of MMHg content in seawater, based on specific extraction and Gas Chromatography Atomic Fluorescence Spectrometry validated according to the requirements of international guidelines and standards, ISO 17025 and Eurachem guidelines, is presented in this study. The entire measurement process was described by mathematical equations and all factors influencing the results were systematically investigated. Selectivity, working range, linearity, recovery (94 ± 4%), repeatability (3.3%-4.5%), intermediate precision (2.9%), limits of detection (0.0004 ng kgas Hg) were systematically assessed. The relative expanded uncertainties obtained were in the range from 16% to 25%, (k = 2). Modelling of the entire measurement process related obtained values for MMHg in seawater to the International System of units (Kg). The potential of this analytical procedure was tested and additionally validated via inter laboratory comparison exercise organised under the Geotraces programme. Obtained results were in excellent agreement with the assigned values. The proposed analytical procedure from the sample preparation to the measurement step combined with the high efficiency of the new generation of the automated MMHg analyzers is fit for purpose for routine monitoring studies on the dissolved MMHg in the costal and open ocean seawaters.