Especiação de arsênio em amostras de atum enlatado por IC-ICP-MS

Abstract

Arsenic is a ubiquitous and potentially toxic element. The Inorganic species [As (III) and As (V)] being of greater concern than the partially methylated species [monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), among others]. Arsenobetaine (AsB) is the species that constitutes the greatest portion of arsenic in marine organisms and is considered inert and non-toxic. The objective of this study was to determine the total arsenic concentration and the concentration of the species AsB, DMA, MMA, As (III) and As (V) in 10 canned tuna fish samples. The total arsenic determination was performed with ICP-MS and the speciation analysis with IC-ICP-MS. The extraction was done using 0.2000 g of freeze-dried sample with 3 mL of 10 mmol.L-1 de NH4(CO3)2 was used for the extraction procedure, in three successive extractions. After the tubes were vortexed for homogenization, they were sonicated at 52 kHz for 15 minutes, centrifuged and the supernatant was separated with the use of a Pasteur’s pipette and put into a new tube. This procedure was repeated two more times and the extract was diluted to a final volume of 10 mL with a solution of 10 mmol.L-1 of NH4(CO3)2 and filtered with a 0.45 µm syringe. The separation was carried out with an anion exchange column and detection was done with ICP-MS, monitoring the mass charge ratio (m/z) 75. For total arsenic determination, samples were prepped with a microwave decomposition method. The limits of quantitation were 0.59 mg.kg-1 (AsB); 0.10 mg.kg-1 (DMA); 0.12 mg.kg-1 (As (III)); 0.07 mg.kg-1 (MMA) and 0.10 mg.kg-1 (As (V)). The method showed that it was free of significant matrix effect (p<0,05). The precision and accuracy of the method were evaluated using certified reference material BCR-627 (tuna fish muscle tissue) (n=5) with certified values of 52 ± 3 µmol.kg-1 AsB and 2.0 ± 0.3 µmol.kg-1 DMA. The obtained experimental values (48.8 ± 1.2 µmol.kg-1 AsB and 1.91 ± 0.16 µmol.kg-1 DMA) were in agreement with the certified values and showed adequate precision within the analytical replicates. In the solid in oil simples the total arsenic content was between 2.65 and 5.81 mg.kg-1 and AsB accounted for 77-85% of the total arsenic content. In the solid in brine simples the total arsenic content was between 2.74-5.70 mg.kg-1 and AsB accounted for 48-76% of the total arsenic content. The other species were below method detection limits, indicating a difference in extraction efficiency between the two conserves, since the means of these percentages were different (p<0.05). The appearance of an unknown peak could indicate degradation of arsenobetaine however, more studies must be done to confirm this affirmation.