Lipid removal by countercurrent chromatography in co-current mode in trace analysis of polyhalogenated compounds in fish

Persistent organic pollutants (POPs) are ubiquitously present in food and environmental samples. Accompanied by similar compounds like halogenated natural products (HNPs), their regular monitoring in fish and their predators is an important task. While different procedures have been developed, the removal of the lipid matrix, mainly carried out by treatment with sulfuric acid or by gel permeation chromatography (GPC), is an indispensable step during sample preparation. Here, we present an alternative, non-destructive method using countercurrent chromatography operated in the co-current mode (ccCCC) for the removal of lipids from the fraction of polyhalogenated compounds in fish. The final method was developed using various POP and HNP standards as well as the most critical lipid compound, i.e. free docosahexaenoic acid (DHA). The recovery rates of polyhalogenated compounds ranged between 79 and 117 %. Applied to six herring (Clupea harengus) fillet samples from the North, the Baltic, and the Norwegian Seas, the results obtained with the new (using ccCCC for lipid removal) method agreed well with those determined with an established method using GPC. The quantitative results indicated that fish from contaminated areas is still a major source in the human uptake of POPs. HNP levels were on average only ∼two times lower than POPs which underscores that they should be monitored on a more regular basis.