Simultaneous speciation of arsenic and mercury in fish by high-performance liquid chromatography inductively coupled plasma mass spectrometry

Abstract

In this study, a method based on liquid chromatography and dynamic reaction cell inductively coupled plasma mass spectrometry (DRC ICP-MS) for the simultaneous speciation of arsenic [As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB)] and mercury [inorganic mercury [Hg(II)] and methyl mercury (MeHg)] in fish was developed. The separation was complete in less than 4.5 min with a ZORBAX SB-Aq C₁₈ column in combination with 5 mmol L⁻¹ 1-octanesulfonate, 5 mmol L⁻¹ acetate buffer and 1% (v/v) isopropyl alcohol (IPA) at pH 4.0 as mobile phase A and 2 mmol L⁻¹L-cysteine in 1% (v/v) IPA (pH 4) as mobile phase B. With O₂ as a reactive gas in the DRC sensitivity of both arsenic and mercury was improved due to the measurement of the former as ⁷⁵As¹⁶O⁺ at m/z 91 and collision damping for both. The detection limits were in the range 0.005–0.007 ng As mL⁻¹ and 0.013–0.015 ng Hg mL⁻¹. To determine the accuracy, a certified reference material (NRCC DORM-3 fish protein) was analyzed where the sum of the concentrations of individual species agreed with total certified concentrations of As and Hg. The developed method was applied on a variety of fish samples. The As and Hg species in fish were quantitatively extracted, into a solution of 1% (v/v) HCl and 0.1% (m/v) Protease XIV taken in a closed centrifuge tube and kept in a pool of water which was heated to 70 °C for 60 min in microwaves. The spike recovery of individual arsenic and mercury species was between 97% and 103%. The precision between sample replicates was better than 7% with the HPLC-DRC-ICP-MS method.