A fast ultrasound-assisted extraction of Ca, Mg, Mn and Zn from vegetables

A fast and accurate method for the extraction of Ca, Mg, Mn and Zn from vegetables is proposed. Ultrasonic energy and dilute acid are used for the extraction. Optimisation conditions for the ultrasonic bath were established: 1 1 of water; 25 degreesC; 2% v/v detergent concentration; horizontal and vertical positions in the bath for sonicating samples: central and bottom, respectively. Using these conditions, the nitric acid concentration (0-1.4 mol 1(-1)), sonication time (0-30 min) and particle size (150-63 mum) were optimised. The best conditions for extraction were: 0.14 mol 1(-1) HNO3, 10 min of sonication time and a particle size < 75 <mu>m. The accuracy of the proposed ultrasound-assisted extraction method was assessed by using certified reference materials, as well as wet digestion. Recoveries ranging from 96 to 102% were obtained under the extraction conditions mentioned above with different kinds of plant samples for the majority of the metals studied. (C) 2001 Elsevier Science B.V. All rights reserved.