Trace Determination Of Cd And Cr(Ⅵ)Based On Atomic Fluorescence Spectrometry

This thesis was mainly focused on liquid phase extractions for solid and liquid samples and electrothermal vaporization sample introduction system based on atomic fluorescence spectrometry.The first part of the thesis developed a procedure for the determination of cadmium with detection by vapor generation atomic fluorescence spectrometry after the cadmium-dithizone complex has been extracted by using a two-aqueous phase system formed by ionic liquid1-isopentyl-3-methylimidazolium bromide and K2HPO4. The cadmium-dithizone complex extracted in the ionic liquid-rich upper phase was acidified with HCl and mixed with NaBH4to facilitate the vapor generation process. The vapor was separated from the reaction mixture in a gas-liquid separator by purging with an argon flow, which was afterwards directed into the atomizer of the atomic fluorescence spectrometer for quantification. A thorough scrutiny has been made to optimize the experimental parameters, including the two-aqueous phase system itself. By using a sample volume of1mL, a linear calibration graph was obtained in the range of0.25-5.0μg L-1, along with a detection limit (3σ, n=7) of0.07μg L-1and a precision of3.4%(n=9,2μg L-1Cd2+). The procedure was demonstrated by analyzing cadmium content in a certified reference material (GBW08608) and real water samples.The second part investigated the determination of chromium based on tungsten-coil electrothermal vaporization as sample introduction system for atomic fluorescence spectrometry. With a sample volume of10μL, a linear calibration graph was obtained within the range of0.5-10μg L-1, along with a detection limit of0.17μg L-1(3σ, n=7) and a precision of3.5%(n=7,5μg L-1). By exploiting methylbenzene and mixed alkali liquor (0.2%NaOH-0.3%Na2CO3) as extractants for leaching Cr from reference material GBW08405polypropylene plastic, an extraction efficiency of up to90%was achieved, giving rise to a relative standard deviation of6.0%(n=9). At pH9,732cation exchange resin was used to differentiate Cr(Ⅵ) and Cr(Ⅲ). Cr(Ⅲ) was retained while Cr(Ⅵ) left in the sample solution, which facilitates its direct determination. This method has been successfully applied to the leaching and determination of Cr(Ⅵ) in the plastic reference material of GBW08404PP.