Development of preconcentration techniques for chemical analysis

In the first chapter of thesis, the effect of nickel salt type used for the preparation of Ni/NixB adsorbent on the arsenic preconcentration was investigated. The nanosorbents were synthesized by reacting NaBH4 with nickel salts. Arsenic sorption efficiencies and capacities of the synthesized nanoparticles were measured in batch studies. Optimization studies were carried out. Langmuir, Freundlich, and Dubinin-Radushkevich (DR) isotherm models were tested and it was found that the sorption was fitted both Langmuir and Freundlich isotherms. The sorption capacity which was obtained from Langmuir isotherms was very high according to literature and was found to be 2.5 g As(III)/g sorbent. DR isotherms showed that sorption is physical and favourable. Hydride generation atomic absorption spectrometer (HGAAS) was used for the determination of arsenic. Nickel interferences which occurred due to the dissolution of the sorbent were eliminated by using a mixture of KI and citric acid. The limit of detection for arsenic determination was comparable with that obtained by other established methods. The developed method was applied to the preconcentration of arsenic in various water samples prior to determination of total arsenic by using HGAAS with satisfactory results. In chapter two, a preconcentration technique by using Ni/NixB sorbent was developed for trace aluminum determination prior to the fluorimetric determination. The sorbent was synthesized by reducing sulfate salts of nickel with NaBH4 in inert atmosphere. Characterization studies were executed by the aid of SEM-EDX, chemical analysis, TGA, XPS and, point of zero charge measurement. It was found that the obtained particles were spherical. Optimization studies were realized. Sorption efficiencies for Al(III) at studied initial pH values between 3-10 were found quantitative. Adsorption rate was quite high and in five minutes sorption efficiencies reached 98.9%. The recovery of Al(III) was found quantitative (˃95%) for sample volumes up to 250 mL. The sorption capacity was found to be 0.394 g Al(III)/g sorbent in batch studies. The sorption capacity obtained from batch studies was compatible with that obtained by isotherm studies. The proposed method was applied to the preconcentration of Al(III) in haemodialysis solutions and various real water samples with satisfactory recoveries.