Graduate Thesis Or Dissertation

 

Development of automated on-line ion exchange systems for the determination of chemical speciation of trace metals in natural waters Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tt44pq032

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  • An automated on-line ion exchange trace enrichment system has been developed to improve the detection limits of flame atomic absorption (AA) spectrophotometry in the determination of trace metals in natural waters. The sample solution is passed through a column of Chelex-100 chelating resin by a carrier buffer stream delivered from a constant flow pump. Trace metal ions retained by the Chelex-100 resin in the column are subsequently eluted off the column using complexing agents such as cysteine and EDTA. The variables that affect the performance of the system are studied. The detection limits of the system with flame AA detection are 0.09 μg/L for Cu and Cd and 0.08 μg/L for Mn with a 10-mL sample loop. The trace enrichment system has also been expanded to an automated two-column ion exchange system to study the speciation of trace metals in natural waters. In the two-column system, the sample solution is passed sequentially through a column of Chelex-100 resin and a column of AG MP-1 macroporous anion resin. The Chelex-100 column retains free metal ions and metal ions dissociated from labile metal complexes. The AG MP-1 column retains anionic non-labile metal complexes and metals strongly associated with negatively charged organic matter such as humic acid. The dissolved metal species are classified into three fractions by the proposed measurement scheme. The variables that affect the results obtained by the two-column system are studied using model complexing agents. The measurement scheme is shown to be rapid and simple (about 10 min per sample with a 10-mL sample loop) and is used to determine the speciation of Cu(II), Cd(II) and Zn(II) in natural water samples. The two-column ion exchange system is a versatile tool to study the trace metal complexation in natural waters. The system is used to determine the trace metal complexing capacity and conditional stability constants of synthetic ligands and ligands in natural waters and to study the dissociation kinetics of trace metal complexes in natural waters. The average Cu(II) complexing capacity of a Willamette River water sample is found to be about 4 μM and the conditional stability constant of Cu(II) complexes is about 10⁷ at pH 7. The apparent 1st -order dissociation rate constant of Cu-humate complexes is determined to be about 0.3 s⁻¹ at pH 6.5.
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