Continuous ultrasound-assisted extraction of cadmium from legumes and dried fruit samples coupled with on-line preconcentration-flame atomic absorption spectrometry

Abstract

Cadmium was continuously extracted with diluted nitric acid from legumes and dried fruit samples using a simple, rapid and continuous ultrasound-assisted extraction system. A minicolumn packed with a chelating resin (Chelite P, with aminomethylphosphoric acid groups) was placed between the extraction unit and the detector for cadmium preconcentration. The cadmium content in the acid extract was retained into the minicolumn, and elution was carried out with hydrochloric acid, with this trace metal continuously monitored by flame atomic absorption spectrometry. An experimental design (Plackett-Burman 2⁶×3/16) was used to optimize the continuous leaching procedure and the preconcentration step. The method allowed a total sampling frequency of 10 and 14 samples per hour for legumes and dried fruit, respectively. The procedure displayed good precision (2.0 and 2.5%, respectively, expressed as relative standard deviations) for samples containing 0.202±0.005 μg g⁻¹ Cd (broad bean) and 0.239±0.004 μg g⁻¹ Cd (peanut). Detection limits of 0.014 μg g⁻¹ Cd for 60 mg of legume samples and 0.011 μg g⁻¹ Cd for 80 mg of dried fruit samples were obtained. The method was successfully applied to the determination of trace amounts of cadmium in legumes and dried fruit samples.