Measurement uncertainty arising from trueness of the analysis of two endocrine disruptors and their metabolites in environmental samples

Evaluation of magnetic nanoparticles to serve as solid-phase extraction sorbents for the determination of endocrine disruptors in milk samples by gas chromatography mass spectrometry

A rapid magnetic solid-phase extraction (MSPE) is proposed based on C18-functionalized magnetic silica nanoparticles as sorbents, for the determination of endocrine disruptors - 20 organochlorine pesticides and 6 polychlorinated biphenyls - in milk samples. Magnetic nanoparticles are characterized by several techniques, such as Scanning Electron Microscopy, X-Ray diffraction, Brunauer-Emmett-Teller and Fourier transform-infrared. The MSPE is performed by dispersion of the Fe3O4@SiO2@C18 nanoparticles in milk samples with sonication, after protein precipitation. Then, the sorbent is collected by applying an external magnetic field and the analytes are desorbed by n-hexane. Several parameters affecting the extraction efficiency of target analytes by the magnetic nanoparticles are investigated, including washing and elution solvents, amount of sorbents, time of extraction and elution, sample and elution solvent volume. The proposed method is optimized by means of experimental design and response surface methodology. When coupled with gas chromatography-mass spectrometry detection and under optimum extraction conditions, average recoveries of target analytes are found to be in the range of 79% to 116%. The proposed MSPE-GC-MS analytical method has a linear calibration curve for all target analytes with coefficients of determination to range from 0.9950 to 0.9999. The limits of quantification are found to be between 0.2 and 1μg/L ensuring compliance with the maximum residue limits established by European Commission and Codex Alimentarius, for OCPs and PCBs residues in milk. The proposed method is applied to the determination of target analytes in milk samples from local markets.

FI-photoinduced chemiluminescence method for diuron determination in water samples

A new method for the determination of the herbicide diuron, using a flow injection manifold and photoinduced chemiluminescence detection, is presented. The pesticide, in basic medium, was irradiated on-line with UV light (254 nm) for 53 s. A short discussion about the possible irradiation products is included. The chemiluminescent response of the photoproducts was induced by oxidation with potassium ferricyanide in phosphate buffer at pH 11.5. The method permitted the quantification of diuron over the 0.1-4.0 mg L(-1) range, with a detection limit (S/N = 3) of 20 µg L(-1) when the method was applied directly. However, the use of solid phase extraction (SPE) performed with C(18) cartridges allowed us to achieve a limit of detection of 0.4 µg L(-1) and a 1.5-30 µg L(-1) dynamic range. The method was successfully applied to the diuron determination in samples of water from different sources (spring, ground, mineral, irrigation, sea and tap waters) with a low consumption of reagents.