# New Method for Simultaneous Arsenic and Selenium Speciation Analysis in Seafood and Onion Samples
## 2 Results and Discussion
### Speciation Analysis of Water-Soluble Arsenic and Selenium by HPLC-ICP-MS
(2008) [41] conducted arsenic speciation in vegetables using trifluoroacetic acid extraction procedure, obtained arsenite and arsenate forms. The As(III) was minor component in the roots of radish, lettuce, and chart with much higher concentrations compared to the present study, while As(V) was dominant in the mung bean roots (more than 15 mg\(\cdot\)kg\({}^{-1}\)) [41]. [PERSON] et al. (2014) found As(III) and As(V) in carrot, lettuce, and spinach after water extraction, but mainly arsenite form in the range 0.01-2.73 mg\(\cdot\)kg\({}^{-1}\) (one result for lettuce root at 89.3 mg\(\cdot\)kg\({}^{-1}\)) [43]. In vegetables (broccoli and cucumber), studies undertaken by [PERSON] et al. (2021) were similar, but only iAs forms were found in the range 0.003-0.024 mg\(\cdot\)kg\({}^{-1}\), which was much lower compared to the concentration of iAs in onion samples [44]. Results of speciation analysis in onion samples are in accordance with As speciation studies with other plants including Pityrogramma calomelanos [45] and Pteris vittata [46], in which was also identified the predominance of As(III) in plant tissue. It can be connected with reduction of As(V) to As(III) as a plant tolerance mechanism, or it can be connected with uptake of As(III) from soil. Moreover, the process of reduction of As(V) to As(III) may limit the As(V) toxicity [41]. Due to the total content of As in onion, [PERSON] et al. (2017) determined average 91.2 mg\(\cdot\)kg\({}^{-1}\) for bulbs and 77.6 mg\(\cdot\)kg\({}^{-1}\) for leaves of onion [46]. When we recalculated the value for iAs concentration as a fraction of 70% of total. As content, we obtained much higher data compared to present and previous studies (iAs- 63.84 mg\(\cdot\)kg\({}^{-1}\) for bulbs and for leaves 54.32 mg\(\cdot\)kg\({}^{-1}\)) [47]. The new method developed here allowed for the simultaneous determination arsenic and selenium forms. Inorganic selenium species were found in most of the samples, but the predominant determined form was Se(VI), especially for seafood, and the major organic form was Se-methionine, which was found in both onions and seafood samples. The highest content of this form was found in white sweet onion. The Se-cystine form was found only in seafood, with the highest content in red shrimp. In the present study, in the onion samples, both inorganic and organic forms were obtained. [PERSON] et al. (2004) found that the extracts obtained from leaves grown in the presence of Se(IV) and Se(VI) obtained Se(VI), Se-cystine, Se-methionine, and Se-methylselenocysteine forms, while in the hot water extract from onion bulbs, similar to the findings in this study, Se-methionine and additional Se-methylselenocysteine were also observed [48]. Further research on selenium speciation in enriched-by-Se(IV) onion samples was conducted by [49]. It should be underlined that they performed only qualitative speciation analysis and obtained for HCl extract Se-methylselenocysteine and Se-methionine forms, while for enzymatic extract, inorganic selenium, Se-cystine, and Se-methionine (the highest signal) forms [49]. In addition, SeMet was the dominant form in enzymatic extracts of plant food such as: buckwheat, green pea, strawberries, rice, cabbage, and kale, which were treatment by Se(IV) [50]. These results are in accordance with the present speciation data for onion samples and can be a confirmation of the statement that SeMet form has been found to be more bioavailable and less toxic than inorganic selenium species [51]. Furthermore, the sum concentration of species of selenium in onion samples was higher compared to seafood data. It can be suggested that this difference may have been caused by the fertilization method used for cultivation due to deficiency of selenium in the soil. [PERSON] and [PERSON] (2007) estimated that, when onions are enriched with Se species, the total selenium content increases significantly, especially in the bulbs, which may lead to higher Se contents in green onion samples [52].