Flow-injection flame atomic absorption spectrometric determination of trace amounts of cadmium in solid and semisolid milk products coupling a continuous ultrasound-assisted extraction system with the online preconcentration on a chelating aminomethylphosphoric acid resin.

摘要

A new sensitive and low-cost method that combines continuous acid extraction, online preconcentration and flame AAS for Cd determination at mug levels in solid and semisolid dairy products is described. A continuous ultrasound-assisted extraction system is used to carry out the dynamic acid extraction step. The acid extract is preconcentrated online on a minicolumn packed with a chelating resin (Chelite P, with aminomethylphosphoric acid groups), and the retained Cd is eluted with HCl and continuously monitored by flame AAS. An experimental design (Plackett-Burman 2^6*3/16) is used to optimize the continuous extraction and the preconcentration step. The method allowed a total sampling frequency of 28 samples/h. The procedure showed good precision (3.0% relative s.d.) for a cheese sample containing 0.103 +- 0.004 mug/g Cd (dry mass). It also showed a high enrichment factor (20.5), and detection and quantification limits of 0.014 and 0.067 mug/g, respectively. The method was successfully applied to the determination of trace amounts of Cd in solid and semisolid milk products, such as cheese and yoghurt.