|M.Sc Student||Japarov Julia|
|Subject||Complex Analytical Method for Detection and Quantification|
of Trace Heavy Metals in Water
|Department||Department of Chemistry||Supervisors||Professor Israel Schechter|
|Dr. Bella Dolgin|
|Full Thesis text|
Various metals undergo reactions with organic reagents, which results in formation of colored complex products. In practice, the molar absorptivities of the complexes allow their quantification in the ppm concentration range. Moreover, proper pre-concentration of the colored complex on a paper filter lowers the quantification limit to the lower ppb concentration range.
In this study, several pre-concentration techniques have been examined and compared: filtering the already complexed mixture/the mixture with pre-formed complexes, complexation on filter, and dipping dye-covered filter in a solution. The best quantification was based on the ratio of filter reflectance at a certain wavelength to that at zero metal concentration. The studied complex formations of Ni ions with 1-(2-thiazolylazo)-2-naphthol (TAN) and Cd ions with 1-(2-pyridylazo)-2-naphthol (PAN) involve production of nanoparticle suspensions, which are associated with complicated kinetics. The size distribution and the kinetics of the complexation of Ni ions with TAN were investigated, such that optimum timing could be found. Kinetic optimization in regard to some interference has also been suggested.
This work also provides evidence for the inhomogeneous nature of these reactions. The complexation has been studied using TEM imaging, zeta-potentiometry, time-dependent particle size analysis and time-dependent spectroscopy. Many of the experimental results are explained in terms of the nature of the nano-particles of these two complexants. Several processes were identified, including crystal growth of the complexant, its reaction with metal ions in solution and on the surface area, chemical erosion of complexant crystallites and their decomposition, re-crystallization of the formed complexes and long term aggregation of both the complexant and the resulted complex. It was found that the needle-like nano-structures on the surface of the TAN particles govern its reaction and particle behavior. The known optimal complexation conditions, such as pH, delay time, etc., have been explained in terms of the zeta-potential minima of the suspensions and in terms of the kinetic parameters. Also the interferences of some ions in the Ni-TAN complexation are now quantified and the kinetic data indicate the best delay time under which the interfering effects are minimal.