Preliminary studies on the stability of arsenolipids: Implications for sample handling and analysis

Human health risk assessments concerning arsenic are now estimating exposure through food in addition to exposure through drinking water. Intrinsic to this assessment is sample handling and preparation that maintains the arsenic species in the form that they occur in foods. We investigated the stability of three arsenolipids (two arsenic fatty acids, AsFA-362 and AsFA-388, and one arsenic hydrocarbon AsHC-332), common constituents of fish and algae, relevant to sample storage and transport, and to their preparation for quantitative measurements. The fate of the arsenolipids was followed by high performance liquid chromatography/electrospray triple quadruple mass spectrometry (HPLC/ESIMS) analyses. Storage of the compounds dry as pure compounds or mixed in fish oil at up to 60˚C did not result in significant changes to the compounds, although losses were observed by apparent adsorption onto the plastic walls of the polypropylene tubes. No losses occurred when the experiment was repeated with glass tubes. When the compounds were stored in ethanol for up to 15 days under acidic, neutral, or alkaline conditions (each at room temperature), no significant decomposition was observed, although esterification of the fatty acids occurred at low pH. The compounds were also stable during a sample preparation step involving passage through a small silica column. The results indicate that these typical arsenolipids are stable when stored in glass at temperatures up to 60˚C for at least 2 days, and that, consequently, samples of food or extracts thereof can be transported dry at ambient temperatures, i.e. without the need for cool conditions.