Graduate Thesis Or Dissertation
 

Exploring a fluorescence-based analytical method for Ba in natural waters and a field study of the major ion chemistry of Lake Issyk-Kul, Kyrgyzstan

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  • Two separate research projects are described here. One involves development of a new analytical method for determination of Ba in seawater and other natural waters. The other is a collaborative field study of the chemistry of Lake Issyk-Kul, Kyrgyzstan. The method project explored an ion chromatography-fluorescence detection bench-top approach for determining dissolved Ba concentrations while at sea or otherwise in the field. Lab work entailed attempts to create a clean buffer, ion chromatographic separation of Ba from potentially interfering major and minor cations (Ca, Mg, Sr) and demonstration of the viability of Ba²⁺ detection by fluorescence of a chelating agent (Calcium Green-i). A linear fluorescence response over the concentration range of 0.03-3.0 μM was obtained which can probably be extended to higher concentrations if required. Time, equipment and financial constraints precluded the intended application of this method to Lake Issyk-Kul samples. It seems likely that the project could be brought to fruition by further exploring pre-concentration issues. A high blank signal in the KH₂PO₄ - NaOH buffer was limiting and potentially cleaner reagents such as NH₄OH should be explored. The blank associated with the chelating agent needs to be investigated. Increasing the sample injection volume, shortening the length of the separation column or employing a concentrator column may also be avenues that would allow successful application of this method. Our portion of a collaborative study of Issyk-Kul entailed major ion analyses of lake, river and well samples. Our results are comparable in magnitude with previously reported data. While the lake level is known to be diminishing at the present, analytical uncertainties are too large to quantify the rate of increase in the salt concentration with time. Major ions appear fairly homogeneously distributed in the lake interior. Residence times for major ions in Lake Issyk-Kul were estimated from our lake data and Russian data for riverine and ground-water inputs. Ions Na⁺ + K⁺, Cl⁻ and SO₄²⁻ have long residence times of 23* 10⁵ yr indicative of strongly conservative behavior. The ion Mg²⁺, has an intermediate residence time (~ 6000 yr). Ions HCO₃⁻ and Ca²⁺ have shorter residence times of ~ 1000 yr or about three times the estimated residence time of water in the lake. Thermodynamic studies show that these latter ions are susceptible to removal within the lake in the form of precipitated carbonate salts. Our data helped provide the basis for our collaborators to derive a lake-specific relationship between conductivity measurements and density. Non-ionic contributions to the dissolved salt composition of the lake generally unimportant. Due to the relatively higher abundance of SO₄²⁻, Issyk-Kul water is denser than seawater diluted to the same absolute ionic salinity. The temperature of maximum density of Issyk-Kul water (2.55 °C) is 0.14 °C lower than seawater diluted to the same absolute ionic salinity. Lake Issyk-Kul water is ~ 1.25 times less conductive than seawater diluted to the same absolute ionic salinity.
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