Method development and analysis of arsenolipids in marine oils

Arsenic in marine oils is mainly present in the form of lipid-soluble compounds; collectively called arsenolipids. Although total arsenic concentrations in marine oils typically range from 0.2 to 16 mg kg-1 [1-3], knowledge regarding the chemical structures and distribution of arsenolipids in oils is limited. The present work describes the development of analytical methods for the determination of arsenolipids, and their application to marine oil, including fish oil and oil of liver of Northeast Arctic cod (Gadus morhua). In the present work gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS) was applied for analysing arsenic-containing hydrocarbons (AsHCs) in fish oil. The AsHCs were extracted into aqueous methanol, and further subjected to solid-phase extraction (SPE) prior to analysis. Reversedphase HPLC-ICP-MS was applied as an analytical technique for analysis of both AsHCs and arsenic-containing fatty acids (AsFAs) in methanol phase of marine oil. The AsHCs and AsFAs were accurately quantified in reversed-phase HPLC-ICP-MS analysis using dimethylarsinate as calibration standard. The molecular structures of the arsenolipids were identified using mass spectrometry. The oils included in the present work contained total arsenic concentrations from 1.6 to 12.5 mg kg-1 oil. Three AsHCs (AsHC-C15, AsHC-C17 and AsHC-C21) were identified as major arsenolipids in all marine oil. Also, two AsFAs (AsFA-C21 and AsFA-C22) were identified as minor arsenolipids in some of the oils. In cod liver, three AsHCs (AsHC-C15, AsHC-C17 and AsFA-C22) and up to five AsFAs (AsFAC15, AsFA-C17a, AsFA-C17b, AsFA-C21 and AsFA-C22) were identified. The present work contributes with data on the presence of arsenolipids, in the form of AsHCs and AsFAs, in a number of marine oils. The developed methods form the basis for future studies on arsenolipids, e.g. the occurrence of arsenolipids in feed and farmed fish.