Figure 3. HPLC/ESI-MS chromatograms of methyl esters.

The chromatograms show less polar arsenolipids (iso-propanol fraction) of blue whiting oil post-silica column (gray line), and the same sample spiked with four standard arsenic-containing fatty acid methyl esters at molecular mass 348, 376, 404 and 450 (black line), prepared by methylation of fatty acids isolated from cod liver oil³. HPLC conditions: Atlantis dC18 (150 × 1.0 mm, 5 μm) at 30°C and a mobile phase comprising a mixture of 10 mM NH₄OAc pH 6.0 and ethanol at a flow rate of 100 μL min⁻¹. The chromatography was performed with linear gradient elution: 0–60 min for 35%–95% ethanol. Selected ion monitoring was performed for [M+H]⁺ at m/z 349, 377, 451 and 405 with fragmentor voltage 150 V. Note: a second signal for m/z 405 ([M+H]⁺) belonged to compound 7 (As-HC404), an arsenic hydrocarbon in the isopropanol extract, which was not changed in the spiking experiment.