Ferrofluid-Based Preconcentration Methods for the Ultra-Trace Determination of Analytes in Complex Matrices with Inductively Coupled Plasma Mass Spectrometry

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Gotam, Yam Nath
Ferrofluid , Preconcentration , ICPMS , Solid phase extraction , Ionic liquid , Noble metals , Potentially toxic elements , Chromium, Arsenic, Selenium species , Platinum, Paladium, Gold, Silver , Ultra-trace determination , Complex matrices
Ultra-trace determination of noble metals and other pathfinder elements is becoming increasingly used as an effective method for mineral exploration to locate undercover ore deposits. For ultra-trace determination of analytes in complex matrices by inductively coupled plasma mass spectrometry (ICPMS), a series of sample preparation steps is required to transform a sample so that it is suitable for analysis and analytes are free of interference. This thesis focuses on the development of preconcentration methods to determine the ultra-trace concentration of analytes in complex matrices. To this end, magnetic nanoparticles (MNPs) of Fe3O4 were used as a sorbent. For the efficient preconcentration of analytes, the surface of MNPs was coated using inorganic coatings (silica, titania) and then functionalized with organic compounds. The functionalized MNPs were characterized with scanning electron microscopy, Fourier Transform Infrared spectroscopy and X-ray diffraction analysis. Ferrofluids (FFs) were then prepared by placing the functionalized MNPs in alcohol or ionic liquid. FFs were injected into the sample solution for the separation/preconcentration of target analytes. A different method was developed for the simultaneous preconcentration of some noble metals (Pt, Pd, Au, Ag) in geological samples than for the determination of potentially toxic elements (PTEs) (As, Cr, Se) in anionic form in waters. Compared to other extraction methods, a FF method is much faster due to the high dispersibility of the FF in the aqueous phase and the fact that phase separation does not require a centrifugation step, as the magnetic separation greatly improved the separation rate. A FF was prepared using 1-octanol as a carrier liquid for the extraction of some noble metals. Under the optimal conditions, recoveries of Pt, Pd, Au, and Ag were above 90%, with an 8-15 fold improvement in detection limits. Moreover, it was successfully applied to a geological certified reference material and provided results in agreement with the certified values for Au, Pt, and Pd according to a Student’s t test. Likewise, with a different FF in an ionic liquid carrier, the recoveries of Cr(VI), As(V), and Se(VI) anions in aqueous solution were also above 90%, with a 20-fold improvement in detection limits.
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