Direct analysis of milk for aluminium using electrothermal atomic absorption spectrometry

This work was conducted in order to develop a sensitive, precise method for the direct determination of aluminium in dairy products without sample pre-treatment. For this purpose, various chemical modifiers and thermal programmes for an electrothermal atomic absorption spectrometer were assessed. Different dry and wet sample pre-treatments were investigated in order to test the applicability of the method to the direct determination of aluminium in the matrices. Aluminium adsorption or leaching in various milk storage materials was also investigated. The proposed method allows the determination of aluminium in the range 5-50 micrograms l-1 and a detection limit of 0.32 micrograms l-1 for aluminium. The precision achieved, expressed as the relative standard deviation, was 5.6% for within-run assays (repeatability) and 12.7% for between-run assays (reproducibility). Various types of commercially available milk (skim, low fat and whole) and milkshake (marketed in different packages) were analysed after dilution to 1 + 3 (v/v) with 0.2% HNO3. Processing whole milk for drinking slightly decreases its aluminium content, but heating in aluminium vessels also slightly increases its content. The reliability of the entire procedure was confirmed by an analysis performed on a Standard Reference Material.