Development of an on-line solid phase extraction method based on new functionalized magnetic nanoparticles. Use in the determination of mercury in biological and sea-water samples.

A new chelating sorbent which employs magnetic nanoparticles (MNPs) functionalized with 1,5-bis(di-2-pyridil)methylene thiocarbohydrazide (DPTH-MNPs) was synthetized and characterized. The aim of the synthesis of this material was to develop fast and simple methods for analysis of trace amounts of metal ions present in biological and environmental samples combining on-line magnetic solid phase microextraction (MSPME) with atomic spectrometry. The MNPs' magnetic core allows overcoming the backpressure problems that usually happen in SPME methods with NPs thanks to the possibility of immobilizing the MNPs by applying an external magnetic field. Thus, a flow injection FI-MSPME/cold vapor generation system coupled to an electrothermal atomic absorption spectrometer (CV-ETAAS) method for the determination of trace amounts of Hg in biological and sea-water samples was developed. A magnet based reactor designed to contain DPTH-MNPs was placed in the injection valve of the FI manifold. Several chemical and flow variables were considered as factors in the optimization process using central composite designs. With the optimized procedure, the detection limit obtained was 7.8ngL(-1) with a precision of 1.7% (RSD) (1.0μgL(-1) Hg). The linear range of the method was studied, and two sections of linear calibration were obtained: from determination limit (0.099µgL(-1)) to 10µgL(-1), and from 10µgL(-1) to at least 50µgL(-1). A preconcentration factor of 5.4 was calculated. The accuracy of the proposed method was demonstrated by analyzing three certified reference materials and by determining the analyte content in spiked sea-water samples. The determined values were in good agreement with the certified values and the recoveries for the spiked samples were in the range of 97.0-107.0%.