Application of factorial design in optimization of ultrasonic-assisted extraction of aluminum in juices and soft drinks

A sample preparation method based on ultrasound-assisted pseudo-digestion of Al from Juices and soft drink samples under ultrasonic effect has been described. A Plackett–Burman experimental design was used as a multivariate strategy for the evaluation of the effects of varying several variables at once. The effects of five different variables preintensification time (without ultrasonic stirring), intensification time in ultrasonic bath (UB), temperature of UB, two acid mixtures (HNO3–H2SO4–H2O2 and HNO3–H2O2), on the recovery of Al have been investigated. From these studies, certain variable showed up as significant, and they were optimized by a using 23 + star central composite design, which involved 16 experiments. The best conditions for pseudo-digestion were as follows: a preintensification time 10 min, intensification time 20 min, volume of acid mixtures 3.0 ml and temperature of ultrasonic bath 80 °C. A conventional acid digestion on electric hot plate was used to obtain total Al for comparative purpose. Final solutions obtained from both methods, were analysed by electrothermal atomic absorption spectrometry. Analytical results for the Al by ultrasound-assisted pseudo-digestion, and conventional wet digestion methods showed a good agreement, thus indicating the possibility of using ultrasonic-assisted digestion sample preparation instead of intensive treatments inherent with the acid digestion methods on electric hot plate. The procedure proposed allowed the determination of Al with detection limit (3ά/s) 10 μg l−1.