# New Method for Simultaneous Arsenic and Selenium Speciation Analysis in Seafood and Onion Samples
###### Abstract  
This paper presents a new method for the simultaneous speciation analysis of arsenic (As(III)-arsenite, As(V)-arsenite, DMA-dimethylarsinic acid, MMA-methylarsonic acid, and AsB-arsenobetaine) and selenium (Se(IV)-selenic, Se(VI)-selenate, Se-Methionine, and Se-Cystine), which was applied to a variety of seafood and onion samples. The determination of the forms of arsenic and selenium was undertaken using the High-Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectrometry (HPLC-ICP-MS) analytical technique. The separation of both organic and inorganic forms of arsenic and selenium was performed using two analytical columns: an anion exchange column, Dionca IonPac AS22, containing an alkanol quaternary ammonium ion, and a double bed cation-anion exchange guard column, Dionec IonPac CG5A, containing, as a first layer, fully sulfonated latex for cation exchange and a fully aminated layer for anion exchange as the second layer. The ammonium nitrate, at pH = 9.0, was used as a mobile phase. The method presented here allowed us to separate the As and Se species within 10 min with a suitable resolution. The applicability was presented with different sample matrix types: seafood and onion. s +
Footnote †: journal: _M molecules_  
0000-0002-2300-23000-2  
exposure to relatively low concentrations of arsenic, cadmium, mercury, and lead can cause health problems [10]. Toxicity is also influenced by the interaction of elements or their forms with each other, and the total toxicity depends on the pH, salinity, and amount and type of dissolved organic matter [11]. According to European Union regulations, the maximum dose of inorganic arsenic in rice and rice products should not exceed 0.3 mg\(\cdot\)kg\({}^{-1}\) fresh mass and should not exceed 0.5 mg\(\cdot\)kg\({}^{-1}\) in aquatic animals and their products [12; 13; 14]. An adequate daily intake of selenium ranges from 15 to 70 \(\upmu\)g a day and depends on age [15]. However, the content of a given element is not enough to determine its toxicity. Different forms of the same element may have different physical, chemical, and toxic properties [16]. For example, the inorganic form of arsenic is more toxic than the organic [1]. Therefore, to define toxicity, biotransformation, and the impact on living organisms of a given element, it is important to research its chemical speciation [17; 18]. Marine products are one of the largest sources of arsenic in the human diet, and over 50 different forms and compounds of this element have been identified [19; 20; 21]. They may contain compounds such as arsenics and arsenates, salts containing arsenic (III) and arsenic(V), MMA, DMA, AsB, and arsenic sugars [21]. Marine organisms, including fish, crustaceans, and seaweed, are high in total arsenic, but more than 90% is in organic form [22]. The inorganic forms of arsenic are more toxic than the organic forms, with arsenic in the third oxidation state being more toxic than in the fifth [23]. MMA and DMA are less toxic than their metabolites, which contain arsenic (III). Arsenobetaine, arsenocholine, and arsenosugars are relatively nontoxic [24]. Toxicity decreases with increasing methylation, so MMA is more toxic than DMA [23]. MMA and DMA are more toxic than arsenosugars but less bioavailable [25]. Inorganic forms of selenium, such as selenite and selenate, show high toxicity in high doses. On the other hand, selenocysteine, Se-methylselenocysteine, and selenomethine, which are organic forms of selenium, have many health benefits [26; 27]. Marine products, including fish and mussels, bioaccumulate selenium and are therefore an ideal source of this micronutrient [28]. On the other hand, vegetables that have a relatively low selenium content, such as onion and garlic, are able to accumulate selenium in high content. In addition, it was suggested that selenium has anticarcinogenic properties. Considering that various species of Aluminum plants, including onions, are Se accumulators, it is worth finding out about the species of this element.