Targeted and Nontargeted Detection and Quantitation of Arsenolipids in a Tuna Fish Reference Material (BCR-627) Using...

This study demonstrates the development of advanced mass spectrometric methodologies suitable for targeted and nontargeted arsenolipid (AsLp) determination in a tuna fish reference material (BCR-627) certified for its arsenobetaine, dimethylarsinic acid, and total arsenic content, thus enhancing its potential to also be used as a noncertified AsLp reference material. Twenty-five As-containing chromatographic peaks were initially detected using reversed-phase high-performance liquid chromatography (HPLC)-inductively coupled plasma-̵̵mass spectrometry (ICP-MS) with a mobile phase consisting of methanol in water ranging from 5 to 95%. Identification of arsenolipids in the detected As-containing peaks was achieved by using a combination of targeted and nontargeted high-resolution electrospray ionization mass spectrometry. Even though the targeted approach confirmed the presence of 11 AsLps already reported to be present in this material, a novel nontargeted approach not only confirmed their presence but also revealed the presence of an additional 26 AsLps, some of which are reported here for the first time. The nontargeted Full MS approach involved accurate mass measurements, better than 1 ppm using a lock mass, for high confidence detection of the AsLps. The resulting mass spectra were subsequently interrogated using the Mzmine software thus allowing for the rapid identification of candidate arsenolipid ions, which were designated to be precursor ions and fragmented in the MS/MS mode. Resulting product ion mass spectra were examined for 5 As-containing marker product ions, all of which are characteristic of the presence of compounds containing a dimethylarsinoyl moiety (CH₃)₂As(O). Precursor ions giving at least 3 marker product ions were identified to be dimethylarsinoyl-containing AsLps. The extracted ion chromatograms for the AsLp molecular ions were overlaid onto the As-specific HPLC-ICP-MS chromatograms for the final confirmation. Based on this approach, a high identification coverage of 84% was achieved, enabling more reliable quantitation of AsLps in BCR-627. By delivering both an analytically validated targeted and nontargeted workflow for AsLp analysis, and an expanded AsLp species dataset, this study provides essential groundwork for more routine, higher-coverage AsLp speciation in marine organisms, with possibilities for interlaboratory comparisons through the use of the BCR-627 tuna reference material. Thus, introducing a new era in AsLp speciation analysis expected to further promote the development of a field that may be referred to as arsenolipidomics.