Renewable column on-line magnetic preconcentration of Cd(II) using FeO nanoparticles functionalized with l-glutamine for determination by flame atomic absorption spectrometry.

This work reports the development of a flow injection analysis (FIA) system for online magnetic preconcentration and determination of Cd(II) in water by flame atomic absorption spectrometry (F AAS). Magnetic nanoparticles of FeO, functionalized with l-glutamine (GlnMNP), were synthesized and used as a support for Cd(II) retention and preconcentration. Each measurement cycle was performed through online complexation of Cd(II) by l-glutamine attached to FeO magnetic nanoparticles at pH 10.5, followed by their retention in a coil due to the action of a cylindrical permanent magnet. Subsequently, the retained magnetic nanoparticles containing Cd(II) were dissolved with an acid solution (4 mol L HCl solution), releasing Cd(II) for transportation to the detector. The main chemical and flow parameters that affected the performance of the system were optimized. Under optimum experimental conditions, the limits of detection and quantification were 2 and 5 μg L, respectively, and a relative standard deviation of 6.5% (at 50 μg L, n = 10) was observed. The FIA system allowed the injection of 24 samples per hour and presented an enrichment factor of four. The method was applied in the analysis of river and pond water samples. The pond water sample was irradiated with ultraviolet light prior to the analysis, in order to eliminate the organic matter. Accuracy of the method was assessed by recovery tests, which provided recovery percentages between 82 and 111%. The developed method was also compared to the direct determination by graphite furnace atomic absorption spectrometry (GF AAS). In this case, the results were not statistical different at 95% confidence level when the Student's t-test was applied.