Multivariate optimization of ultrasound-assisted extraction procedure for the determination of Cu, Fe, Mn, and Zn in plant samples by Flame Atomic Absorption Spectrometry

In this work, a simple, easy and fast ultrasound-assisted extraction procedure for the determination of Cu, Fe, Mn, and Zn in plant samples was developed. Sample preparation conditions were optimized in a multivariate manner using mixture design and Box-Behnken. The extraction condition adequate to obtain the maximum response was 90% power, 10 minutes, 40 °C temperature, using extraction solution composed of HNO3 and HCl in the concentration of 0.5 and 1.1 mol L-1, respectively, for a volume 10 mL and 250 mg of sample. Accuracy was verified from the analysis of certified reference material (Apple leaves, NIST 1515) yielding recoveries between 89 and 98% for procedure. Precision was evaluated in a repeatability study (n=10), yielding RSDs less than 6.7%, and the limits of quantification (mg kg-1) were 0.95, 2.42, 1.31, 1.18 for Cu, Fe, Mn, and Zn, respectively. The concentrations determined in the stem and leaf of the mangrove species varied according to the collection point and the tissue, being consistent with other studies. The proposed procedure was efficient and reliable for the elemental determination in plant samples, with the advantage of low cost and reagent consumption besides short analysis time as a valid alternative to conventional sample preparation procedure.