Determination of aluminum in Canadian duplicate diets by a combination of thermal and epithermal instrumental NAA as well as by cloudpoint extraction preconcentration NAA

Exposure to aluminum is of public concern due to its potential toxic biological effects and possible association with Alzheimer's disease. Aluminum is a rather difficult element to determine by almost all analytical techniques. A combination of instrumental NAA (INAA) and epithermal INAA (EINAA) was applied in the present work using the Dalhousie university SLOWPOKE-2 reactor facility. The 1779-keV gamma-ray of ²⁸Al produced by the reaction ²⁷Al (n,γ)²⁸Al was used for the determination of aluminum. EINAA was used to correct for contribution to the ²⁸Al activity produced by the interfering reaction ³¹P (n,γ) ²⁸Al from phosphorus present in the samples. Our results for the reference materials analyzed by the combination of the INAA/EINAA method agreed well with the certified values. This combined method was applied to 15 Canadian duplicate diet samples. The dietary intakes (dry weight, mg/d) for this population group had a mean of 7.0, median of 4.4, and a range of 0.08-32. Additionally, a preconcentration NAA (PNAA) method using cloud point extraction (CPE) was developed for not only to concentrate aluminum but also to significantly reduce phosphorus. The CPE method used phenylphenol ether 7.5 as the surfactant and 8-hydroxyquinoline as the chelating agent. The effects of ionic strength, pH, equilibration temperature, surfactant concentration, and chelating agent concentration were investigated with respect to the extraction potentials of aluminum and phosphorus. The system was shown to exclude phosphorus below the detection limits of NAA and to produce extraction efficiencies of about 90% for aluminum standards. (author)