Graduate Thesis Or Dissertation
 

A reaction rate determination of aluminum with a microcomputer-based spectrofluorometer

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nk322h880

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  • The development and optimization of a fluorometric reaction rate method for the determination of aluminum is described. Modifications to existing instrumentation permit automatic monitoring and reporting of measurement conditions. Automatic correction of measured analytical signals is provided if monitored parameters deviate from optimum values. A computer controlled standard addition procedure was developed to permit rapid analysis of samples when quenching or strong matrix absorption interferes with normal measurements. The rate of formation of the fluorescent aluminum chelate of 2, 4, 2' - trihydroxyazobenzene - 5' - sulfonic acid is measured and related to the concentration of aluminum. The technique exhibits a detection limit of 0.12 ng/mL and a large linear dynamic range over four orders of magnitude. A thorough interference study was conducted and no serious interferences were discovered which would preclude the use of the method in analyses of natural waters. The technique was successfully applied to an analysis of NBS spinach leaves and to a river water sample. Modifications to the existing fluorometric reaction rate instrument include the addition of a pH probe and meter and a temperature probe and meter interfaced to a KIM microcomputer through a multiplexed analog-to-digital converter. In addition, an automatic injector was modified and installed on the instrument to provide automated standard additions. The existing KIM singleboard microcomputer was enhanced by additional memory, I/O capability and BASIC software plus a CRT terminal and an ASCII serial alphanumeric printer. Separate computer programs were developed for general analyses and for standard addition measurements. Software was developed with the intention of providing a highly automated system in which measurement parameters are monitored and reported and all data collection and manipulation is performed automatically. Software correction of analytical signals is shown to improve measurement precision by a factor of four when reaction mixture temperatures vary over 1.05 °C, and by more than an order of magnitude when reaction mixture pH varies over 0.28 pH units. Improved measurement accuracy results from software correction of measured signals: a measurement error of 40 % incurred as a result of low reaction mixture temperature and pH was reduced to 0.13 %. The automated standard addition procedure is shown to be effective in dealing with error incurred by the presence of matrix quenchers or absorbers with measurement errors reduced from 40 % to less than one percent.
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