A new analytical strategy for single extraction of metals in phosphate fertilizers

Abstract

A simple method using an ultrasound-assisted single extraction procedure for the determination of Cd, Pb and Cr in phosphate fertilizers by graphite furnace atomic absorption spectrometry was developed. Multivariate optimization through a factorial design and desirability functions was applied to establish a single extraction procedure for the metals. Quantitative extraction was carried out with 20 mL of a mixture of 1 mol L⁻¹ HNO₃ and 1 mol L⁻¹ HCl applying sonication for 7.5 min. Under the optimal conditions the characteristic mass and limits of quantification were 0.54, 8.22 and 2.54 pg and 0.11, 0.90 and 0.63 μg L⁻¹ for Cd, Pb and Cr, respectively. The relative standard deviation was less than 5%. The accuracy of the method was evaluated by comparison with the results obtained from the analysis of a multi-nutrient fertilizer (certified material NIST SRM 695) and no significant difference at the 95% confidence level was observed. The method was applied to the extraction and determination of Cd, Pb and Cr in phosphate fertilizer samples produced in Brazil and the levels found were below the maximum values established by Brazilian legislation.