Optimisation by experimental design of an IEC/ICP-MS speciation method for arsenic in seafood following microwave assisted extraction

Abstract

An experimental design was used to optimise a speciation method involving ion exchange chromatography coupled to inductively coupled plasma-mass spectrometry (IEC-ICP-MS) for the determination of arsenic species in fish samples following a microwave-assisted extraction (MAE). The effects of several factors (eluent composition and concentration, gradient program, mobile phase flow rate, column temperature and plasma power), and their possible interactions on the arsenic species separation and detection, were evaluated using an experimental design in order to establish the optimal conditions. Two mobile phases (A and B) composed of HNO₃ (0.5 and 50 mmol L⁻¹ respectively) and MeOH (1%) were used in a gradient consisting of 100% A for 2.5 min, 10% A for 3 min, and 80% A for 5 min, on a Dionex Ionpac AS 7 high-capacity anion-exchange column maintained at 20 °C, with a mobile phase flow rate of 1.35 mL min⁻¹ and a rf-power to the plasma of 1450 W. Under these optimised conditions, seven different arsenic species (As^III, As^V, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, trimethylarsine oxide) could be separated within 11 min in a single chromatographic run. Limits of quantification ranged from 0.008 to 0.042 mg As kg⁻¹, which were generally similar to those previously reported. Moreover, trueness was estimated on three different certified reference materials of fish after MAE with 10 mL of methanol–water mixture (8 + 2 v/v). In all cases the results were in good agreement with the certified values.