Speciation Analysis By Atomic Fluorescence Spectrometry Hyphenated Techniques

This dissertation deals with atomic fluorescence spectrometry (AFS) based on-line hyphenation techniques for speciation analysis and stability study of mercury species. It consists of the following chapters.In Chapter 1, on-line hyphenation techniques of AFS with gas chromatography, high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) were reviewed with emphasis on the interface design and analytical applications. Factors affecting the stability of inorganic mercury and methylmercury during storage were reviewed. Several possible proposed mechanisms for mercury losses and various reported approaches for prevention of such losses were discussed.In Chapter 2, cloud point extraction was applied for simultaneous preconcentration of Hg(II), methylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) prior to HPLC-CV (cold vapor)-AFS. The four mercury species were taken into complexes with ammonium pyrrolidine dithiocarbamate (APDC) in Triton X-114 medium and concentrated in the surfactant-rich phase by bringing the solution to the temperature of 40℃. Baseline separation of the enriched complexes was achieved on an ODS column with a mixture of methanol, acetonitrile and water (65:15:20, v/v/v) as the mobile phase (pH 3.5). A post-column oxidation of the elute solution from HPLC, in the presence of K₂S₂O₈ in HCl, was applied to convert organomercury compounds into Hg(II) for cold vapor generation. The preconcentration of 10 mL of sample solution gives enhancement factors of 29, 43, 80 and 98 for MeHg, EtHg, PhHg and Hg (II), respectively. Detection limits (3σ) ranged from 0.1 to 0.9 ng L^-1 (as Hg). The developed method was successfully applied to the speciation of mercury in real fish samples.In Chapter 3, CE coupled with hydride generation (HG)-AFS was developed for the speciation analysis of organotin compounds. The four organotin cations of trimethyltin, monobutyltin, dibutyltin and tributyltin were completely separated by CE in a 50 cm×75μm i.d. fused-silica capillary at 20 kV and using a mixture of 50 mmol L^-1 H₃BO₃-50 mmol L^-1 Tris-10% v/v methanol (pH 7.10) as electrolyte. 0.008 mmol L^-1 CTAB added to the electrolyte suppressed the adsorption of the organotin cations on the inner wall of capillary. The generated hydride species were on-line detected with AFS. The relative standard deviation (RSD, n = 5) were in the range of 1.7 to 3.1% for migration time, 3.8 to 4.7 % for peak area response, and 1.6 % to 2.8% for peak height response for the four organotin species.In Chapter 4, a rapid, sensitive, and cost-effective method was developed for the determination of trace mercury in water samples by on-line coupling of flow injection sorption preconcentration with oxidative elution to CV-AFS. Trace Hg(II) in aqueous solution was preconcentrated by on-line formation of mercury diethyldithiocarbamate complex (Hg-DDTC) and adsorption of the resulting neutral complex on the inner walls of a PTFE knotted reactor. A mixture of 16% v/v HCl and 10% v/v H₂O₂ was used as the eluent to remove the adsorbed Hg-DDTC from the KR, then convert on-line the Hg-DDTC into Hg(II) prior to its reduction to elemental mercury by KBH4 for subsequent on-line CV-AFS detection. No serious interferences from the organomercury species of methylmercury, ethylmercury and phenylmercury up to 0.5 mg L^-1 were observed for the preconcentration of Hg (II) in the developed system. With a sample loading flow rate of 3.1 mL min^-1 for a 60 s preconcentration, a detection limit (3a) of 4.4 ng L^-1 was achieved at a sample throughput of 36 samples h^-1. The method was successfully applied to the determination of mercury in a certified reference material, GBW(E) 080392, and a number of local natural water samples.In Chapter 5, CV-AFS and HPLC-CV-AFS were used to study the stability of mercury species in fish samples during sample treatment. From the preliminary results obtained it can be concluded that fresh fish sample show good stability against temperature during microwave oven and oven drying. On the other hand, significant species interconversion takes place during the pH adjustment of fish sample extract. This implies that the HC1 leaching provides a source of error in mercury species determination because of species interconversion. More effort should be made to solve the problems associated with the stability of mercury species.