Simultaneous Determination of Trace Mercury, Cadmium and Lead in Fish Sauce Food Matrix by Diffusive Gradients in Thin Films Technique

Fish sauces are popular seasoning liquid originating in south-eastern Asian cuisine, consisting of fermented fish, salt and additional ingredients. Fish used for production could be part of geobiochemical cycle of many contaminating metals, some of which could be potentially hazardous for human health if long-term consumed in larger quantities. Therefore, monitoring of fishery products is required for sustaining food safety and quality. Due to the relatively low concentration of metal contaminants, high saline content and complicated matrix effect, direct analysis of fish sauce by common analytical techniques could be challenging. Possible pre-treatment steps to avoid that, however, include considerable dilution of the sample. That could the concentration of analytes of interest to decrease close or below the limits of the instrumental technique used. In this work, the environmental passive sampling tool - Diffusive Gradients in Thin Films (DGT) technique utilizing Chelex-100 and Purolite S924 resin gel and is used for determination of dissolved mercury (Hg), cadmium (Cd) and lead (Pb) in fish sauce. The method was validated by two basic tests: a linear metal accumulation over time and the reciprocal diffusion gel thickness. Due to fish sauces’ high salinity levels, the effect of the NaCl concentration on the determination of selected metals was also studied. Metal concentration in deployment solution and the mass of metal accumulated on resin gels and was analysed after elution by SF-ICP-MS. After that validation step, the DGT technique was used for the analysis of real fish sauce samples purchased in the retail network, where the content of hazardous metals did not exceed the limit set by the EU legislation for fishery products. Due to the preconcentration ability of DGT, much lower concentration levels of Hg, Cd and Pb could be detected, compared to microwave digestion of sample combined with SF-ICP-MS analysis. Therefore, DGT offers a non-destructive alternative method for trace element analysis in complex food matrices.