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Application of Fractional Factorial Design and Doehlert Matrix in the Optimization of Experimental Variables Associated with the Ultrasonic-Assisted Acid Digestion of Chocolate Samples for Aluminum Determination by Atomic Absorption Spectrometry

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A simple and rapid method based on ultrasound energy is described for the determination of aluminum (Al) in complex matrixes of chocolate and candy samples by electrothermal atomic absorption spectrometry. The optimization strategy was carried out using multivariate methodologies. Five variables (temperature of the ultrasonic bath; exposure time to ultrasound energy; volumes of 2 acid mixtures, HNO3H2SO4H2O2 (1 + 1 + 1) and HNO3H2O2 (1 + 1); and sample mass) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using fractional factorial and Doehlert matrix designs. Validation of the ultrasonic-assisted acid digestion procedure was performed against standard reference materials, milk powder (SRM 8435) and wheat flour (SRM 1567a). The proposed procedure allowed Al determination with a detection limit of 2.3 g/L (signal-to-noise = 3) and a precision, calculated as relative standard deviation, of 2.2 for a set of 10 measurements of certified samples. The recovery of Al by the proposed procedure was close to 100, and no significant difference at the 95 confidence level was found between determined and certified values of Al. The proposed procedure was applied to the determination of Al in chocolate and candy samples. The results indicated that cocoa-based chocolates have higher contents of Al than milkand sugar-based chocolates and candies.
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Document Type: Research Article

Affiliations: University of Sindh, Center of Excellence in Analytical Chemistry, Jamshoro, Pakistan.

Publication date: November 1, 2007

More about this publication?
  • The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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