Toward High Precision Isotope and Trace Elements Analysis in River water and Coral Skeleton: Analytical Methods Development and Application

Autor: Chuan-Hsiung Chung, 鍾全雄
Rok vydání: 2009
Druh dokumentu: 學位論文 ; thesis
Popis: 97
The application of proxies to studies of past ocean chemistry requires both understanding of the systematic and limitations of the proxies, and development of appropriate analytical methodology to produce data with the accuracy, sensitivity and resolution necessary to permit reliable interpretation. The purposes of this research are to develop analytical methods for high precision and accuracy analysis of trace elements concentration and isotope rations in natural samples by advanced mass spectrometric techniques. Then apply these methods can be used to retrieve environmental information from various archives. The systematic and limitations of coral proxies is assessed by a culture experiment. For more comprehensive understanding of the element transportation from land to sea which can affect the elemental composition of coral skeleton, water chemistry of Kaoping river located on southwestern Taiwan were also studied using high precision Sr isotope and REEs data. Analytical performances of conventional microconcentric nebulizer (MCN) and thermal membrane-desolvation sample introduction systems (Aridus) were compared for determination of low concentrations of rare earth elements in surface and subsurface waters using a double focusing magnetic sector inductively coupled plasma mass spectrometer. Conventional figures of merit were employed, such as REE sensitivities, limits of detection (LODs), memory effects, BaO+ and BaOH+ polyatomic ion interferences, % REE-oxide formation, matrix induced no spectroscopic interferences, long term signal variations, and recovery from spiked sea water samples and CRMs. In general abundance corrected mass distributions for the MCN were quite flat with exception of LREEs which were dependant on REE-O+ polyatomic ion generation. REE sensitivities varied from about 0.3-0.6 MCPS/ppb for 139La+, 140Ce+ and 141Pr+, and to 0.8-1 MCPS/ppb for the remainder of the REEs. In contrast, Aridus responses varied from about 3.5-4.3 MCPS/ppb i.e. signal enhancement factors of 4 to 10. LODs varied from 0.05-0.3 ppt and 0.1-0.2 ppt for the MCN and Aridus systems, respectively. Method accuracy was determined by analyzing a spiked sea water CRM NAAS-5 (1:100 v/v) with 1 µg L-1 REEs and CRM SLRS-4 using an external calibration procedure. The use of Tb with the MCN failed to compensate for LREE variations, but recoveries of MREEs and HREEs were about 95 to 100 %. With the Aridus system uncompensated recoveries were about 85 % for all REE and were about 100 % with Tb. Long term REE determinations of NRC SLRS-4 were in good agreement with the reported values indicating that very low REE concentrations can be determined directly without matrix separation and analyte preconcentration. In routine analysis operating conditions were optimized so that the measured CeO+/Ce+ ratios were less than 1 %. These conditions are obtainable using the Aridus system which was preferred for routine diagnostic REE determinations in surface and subsurface waters in Taiwan A high precision analytical method of Fe isotope measurement for low concentration samples was developed using HR-MC-ICPMS. Several parameters that may affect the accuracy and precision of 56Fe/54Fe result such as background, instrumental mass discrimination, isobaric interferences, type of introduction system and acid molarity were identified and evaluated. External precisions better than 0.04‰ for δ56Fe can be achieve using only 10ng of iron sample with APEX and X-cone as introduction system. Compare of this study and previous ones shows that significant improvement in terms of sample size was made. Only one tenth of sample amount is needed to get similar precision. This method can be applied on very low concentration samples such as coral and seawater. The systematic and limitations of coral proxies is assessed by a culture experiment to improve our understanding of the relationships between the proxies and parameters of interest. Sr/Ca variation is mainly controlled by temperature confirming that Sr/Ca ratios in coral skeletons while the kinetic effect may dominate the stable isotopic fractionations. For more comprehensive understanding of the element transportation from land to sea which can affect the elemental composition of coral skeleton, water chemistry of Kaoping river located on southwestern Taiwan were also studied using high precision Sr isotope and REEs data. The 87Sr/86Sr variations are rather large from 0.712649 to 0.713592 and show systematically decreasing ratios with distance from the coastal region. The dissolved REE patterns of the KPR at different tributaries including Laonong River, Cishan River and Baolai River show similar negative Ce anomaly and HREE enrichment. Strong positive Gd anomaly supports an anthropogenic pollution in the river. The REEs patterns may not be reflective of total weathering processes because their distinct behavior in river system. The methods developed in this study are very broad applicable techniques. The systematic assessment criteria of the analytical methodology describe in this thesis can been applied to other elemental or isotopic measurement, for instance, Nd isotope in coral skeleton which can be used to trace the terrestrial input.
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