Development and validation of a non-chromatographic method for mercury and methylmercury in finfish using thermal decomposition gold amalgamation atomic absorption spectrophotometry (TDA-AAS) and salting-out assisted liquid–liquid extraction (SALLE)

Accurate technologies and methods are needed to monitor both total and methylmercury in the marine food supply. Thermal decomposition gold amalgamation atomic absorption spectrophotometry (TDA-AAS) is an efficient and cost-effective technique for measuring low levels of total mercury requiring no sample preparation. Measuring methylmercury with TDA-AAS requires isolating methylmercury from the matrix and other mercury species prior to detection. We developed a method that uses ethyl acetate instead of a legacy non-polar solvent, toluene. Toluene is a potentially hazardous and problematic solvent whereas ethyl acetate is greener and safer. Additionally, the salting-out assisted liquid-liquid extraction (SALLE) approach with ethyl acetate avoids emulsion formation throughout extraction. We describe method development and validation of a SALLE and TDA-AAS detection for methylmercury in finfish. From 10 reference materials, our method recovered 80-118% of total or methylmercury with Z scores ranging from -1.98 to 2.75 (n = 184). The LOD and LOQ of the method for methylmercury were 3.8 and 27 ng/g, respectively. From extraction to detection, accurate results were obtained from a sample in less than 2 h for both total mercury and methylmercury.