Graduate Thesis Or Dissertation
 

Development of trace enrichment techniques for trace metals in natural waters using high pressure liquid chromatography

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0v8383815

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  • An on-line trace enrichment (TE) system, based on high pressure liquid chromatogroaphy (HPLC) and flame atomic absorption (AA), has been developed for trace metal analysis. The sample is pumped through a column filled with a cation exchange resin which traps metal ions. The ions are subsequently stripped from the column with citrate solution and pass directly into the AA for quantitation. Calibration is achieved with an 87 μ L sample loop which introduces standard solutions directly onto the column without going through the pump. A microcomputer system interface was constructed which performs instrumental control and data handling functions. The system was tested with three representative elements - Cu, Cd, and Mn. Detection limits with the sample loop were found to be about 5 ng for all three test metals. The limitation on detection of dilute analyte solutions was tested by determination of 0.3 μg/L solutions for each metal, using a 50 mL TE. Lower concentrations could presumably be determined by use of a larger TE volume. Precision for replicate runs is typically better than 5-10% relative standard deviation (RSD), and linearity of the system was found to extend from the detection limit to approximately 5 mg/L for all three metals. Thus a sample can be determined if its concentration is in the range of at least 0.3 μg/L to 5000 μg/L, or over 4 orders of magnitude. Sample throughput time depends on sample concentration, and it takes about 20 minutes to analyze samples in triplicate at the μg/L level. About 20 minutes are necessary to generate a calibration curve. An interference study was made of species most commonly found in natural water samples. The system was found to be free from interference effects from them at levels higher than that expected in most real samples. The 3 metals were also determined in river and tap water samples. The concentration of Cu was found to be 1.2 mg/L in tap water and 2.6 μg/L in river water. Cd was found to be 0.25 μg/L in tap water and 0.22 μg/L in river water, while Mn was 2.3 μg/L in tap water and 9.5 μg/L in river water. These results were verified by a standard addition procedure to assure that the system was not subject to significant interference effects.
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