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Title: Method development for the analysis of chromium in the environment and its speciation in water samples
Other Titles: Ge yuan su zai huan jing zhong fen xi fang fa de fa zhan ji qi zai shui yang pin zhong xing tai yan jiu
Authors: Ma, Hoi Ling (馬凱玲)
Department: Dept. of Biology and Chemistry
Degree: Master of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Chromium -- Environmental aspects
Notes: CityU Call Number: TD196.C53 M3 2006
Includes bibliographical references (leaves 189-208)
Thesis (M.Phil.)--City University of Hong Kong, 2006
xvii, 208 leaves : ill. (some col.) ; 30 cm.
Type: Thesis
Abstract: A more precise and accurate analytical method is required to quantify the occurrence of chromium (Cr) in the ambient atmosphere. The development of new methods and the improvement of existing methods for analyzing Cr in air, dust and water were reported in this thesis. An instrumental method for analyzing trace levels of Cr by inductively coupled plasma - dynamic reaction cell - mass spectrometry (ICP-DRC-MS), utilizing ammonia reaction gas, has been developed. The detection limit obtained was in the region of 0.002–0.366 ng ml-1 for different Cr isotopes. DRC technology was effectively employed to minimize polyatomic interfering species 40Ar12C+, 1H35Cl16O+, 40Ar13C+ and 37Cl16O+ in 52Cr and 53Cr determination. A multi-stage microwave digestion programme using HNO3, H2O2, HF and H3BO3 was well developed to enhance the complete digestion of Cr for subsequent analysis. Total suspended particulate matter (TSP) was collected at CityU (CityU) campus and EPD’s Kwun Tong (KT) monitoring station during February 2005 to August 2005, using high-volume air samplers. The 52Cr concentration determined by ICP-DRC-MS, was higher at KT, and was in the range from 5.8–32.3 ng m-3 at both sites, with an average value of 13.2 ng m-3. Concentrations of gaseous SO2, NOx, NO2, NO and O3 at KT averaged over the sampling period have been correlated with the measured Cr concentration, and the relationships between the measured concentration of Cr and the concentrations of other elements (Na, Mg, Al, K, Ti, V, Mn, Fe, Co, Cu, Zn, As, Cd, Ce and Pb) have been reported. The correlations suggested the emission from construction sites, fuel combustion, soil, vehicles and industries are the possible contributing sources of Cr and their relative proportions vary at different locations. 25 street dust samples were collected from different locations across Beijing, Shanghai and Hong Kong. Their particle size distributions were studied and compared by using the Environmental Scanning Electron Microscope (ESEM) and image analysis software. Higher proportions of fine particles were found in Beijing and Shanghai than in Hong Kong. The size distributions of street dust particles were compared with that of the particulate matter and comparable results were obtained except in Hong Kong. The average Cr concentration of 323.9 mg kg-1 in Hong Kong was found to be the highest among the three cites. Higher Cr concentrations were found in smaller dust particle size fractions and occurred near the roadside. Concentrations of different elements (C, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Rb, Cd, Ce, Hg and Pb) have been correlated with the measured Cr concentration and the compositions of street dust particles have been compared with that of the TSP samples. The determined elemental concentrations were compared with the concentrations obtained by XRF measurement and reasonable agreement was obtained. It appears that Cr in sheet dust mainly arises from traffic-related and crustal sources. A speciated isotope dilution method was developed using ICP-DRC-MS for the analysis of Cr in water samples and the assessment of interconversion between Cr(III) and Cr(VI). The method was applied to the analysis of local nullah water. About 90% of Cr in nullah water was found to be in the hexavalent form. The percentage of conversion from Cr(III) to Cr(VI) (α) increases with increase of the concentration of Cr(VI) and Cr(III), while the increase of the percentage of conversion from Cr(VI) to Cr(III) (β) is relatively less significant. The time of sample storage increased α and β. The equilibrium constant for interconversion is considerably constant.
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