Espécies de arsênio em moluscos bivalves determinadas por LC-ICP-MS E LC-CVG-ICP-MS após extração assistida por microondas

Abstract

In this work, the aim of this study is to evaluate sample preparation procedures and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) and LC coupled to chemical vapor generation (CVG) and ICP-MS (LC-CVG-ICP-MS) for identification and quantification of As species in mollusks collected in BTS. Conditions related to As species extraction were assessed with the use of microwave assisted extraction (MAE) and ultrasound-assisted extraction (UAE). The influence of the main parameters involved in extraction of As species such as the type and concentration of extraction solution, sample mass, temperature and extraction time were evaluated. The extraction was possible by using water at 80 °C (0.2 g sample and 6 mL of w ater) for 6 min using MAE. For the chromatographic separation the type of mobile phase [(NH4)2CO3 and (NH4)2HPO4] concentration (1 to 20 mmol L-1), pH (5.0 to 9.0), flow rate (1.05 to 1.45 mL min-1) and elution mode (isocratic and gradient) were evaluated. The volume of sample injected into the chromatograph was fixed to 200 μL. For the separation of As species an anion exchange column (Hamilton PRP-X100, 250 x 4.1 mm) was used. Six As species were detected in the mollusks being identified arsenobetaine (AsB), As(III), dimethylarsenic acid (DMA) and ρ- arsanilic acid (ρ-ASA). The best separation of the As species was obtained by gradient elution mode and using the following program: 0 to 1.4 min using 6 mmol L-1 (NH4)2HPO4 to 1.4 to 2.7 min using 20 mmol L-1 (NH4)2CO3 and 2.7 to 15 min using 6 mmol L-1 (NH4)2HPO4). The mobile phase flow rate was set at 1.25 mL min-1. CVG parameters were evaluated and the concentrations of NaBH4 and HCl, and carrier gas flow rate were set to 1.0% (m/v) 1.0 mol L-1 and 1.15 L min-1, respectively. The extraction procedures and determination of total As were evaluated using certified reference materials BCR 627 (Tuna Fish Tissue), DORM-2 (Dogfish Muscle) and NIST 1566b (Oyster tissue). The agreement of the results obtained was 95 ± 3 to 101 ± 5%, respectively. The sum of the concentrations of As species determined by LC-ICP-MS and the total As concentration in digested samples and extracts measured, determined by ICP OES were also in good agreement on a confidence level of 95% (Student t-Test). The developed methods by employing the LC-ICP-MS and LC-CVGICP- MS for As speciation analyses in bivalves mollusks are considered suitable.