Simultaneous determination of arsenic and selenium species in fish tissues using microwave-assisted enzymatic extraction and ion chromatography–inductively coupled plasma mass spectrometry

A microwave-assisted enzymatic extraction (MAEE) method was developed for the simultaneous extraction of arsenic (As) and selenium (Se) species in fish tissues. The extraction efficiency of total As and Se and the stability of As and Se species were evaluated by analyzing DOLT-3 (dogfish liver). Enzymatic extraction using pronase E/lipase mixture assisted by microwave energy was found to give satisfactory extraction recoveries for As and Se without promoting interspecies conversion. The optimum extraction conditions were found to be 0.2 g of sample, 20 mg pronase E and 5 mg lipase in 10 mL of 50 mM phosphate buffer, pH 7.25 at 37 °C. The total extraction time was 30 min. The speciation analysis was performed by ion chromatography–inductively coupled plasma mass spectrometry (IC–ICP–MS). The accuracy of the developed extraction procedure was verified by analyzing two reference materials, DOLT-3 and BCR-627. The extraction recoveries in those reference materials ranged between 82 and 94% for As and 57 and 97% for Se. The accuracy of arsenic species measurement was tested by the analysis of BCR 627. The proposed method was applied to determine As and Se species in fish tissues purchased from a local fish market. Arsenobetaine (AsB) and selenomethionine (SeMet) were the major species detected in fish tissues. In the analyzed fish extracts, the sum of As species detected was in good agreement with the total As extracted. However, for Se, the sum of its species was lower than the total Se extracted, revealing the presence of Se-containing peptides or proteins.