Aluminium Determination in Foodstuffs by ICP-MS: Influence of Microwave Digestion Parameters on the Recovery

Aluminium (Al) is the third most common element in the Earth’s crust and occurs naturally in drinking water and agricultural products, and humans are consequently exposed to the element from dietary sources. A tolerable weekly intake of 1 mg/kg has been established by the European Food Safety Authority (EFSA); however, no maximum levels for aluminium in foodstuffs have so far been established in the European Union (EU) legislation. Official food control requires validated methods for the determination of aluminium. Acid digestion assisted by microwaves is the main sample preparation technique used for the determination of aluminium, usually in combination with atomic spectrometry for quantification. In the present study, different parameters in the digestion step were investigated including test portion, digestion temperature, the reagent used and duration of the digestion to assess the aluminium extraction. The presented work is following up on an observation from a proficiency test (PT) on trace elements (including aluminium) in cocoa powder organised in 2020 by the European Union Reference Laboratory for metals and nitrogenous compounds in feed and food (EURL-MN), where the participant results for aluminium showed an unexpectedly large variation. In addition to the PT material, different certified reference materials were included in the present study, and the results highlighted that the temperature and reagent used are the most critical parameters to obtain a satisfactory sample digestion prior to aluminium determination. Based on the obtained results, it is recommended to digest food samples with a mix of ultrapure water and nitric acid for 25 min at a temperature of at least 240 °C with a mix of HNO3 and H2O to achieve satisfactory microwave-assisted digestion.