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Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry
Hamner, Vincent N.
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HYDROXYPROPYLMETHYLCELLULOSE: A NEW MATRIX FOR SOLID-SURFACE ROOM-TEMPERATURE PHOSPHORIMETRY by Vincent N. Hamner R.E. Dessy, Chairman Chemistry (Abstract) This thesis reports an investigation of hydroxypropylmethylcellulose (HPMC) as a new solid-surface room-temperature phosphorescence (SSRTP) sample matrix. The high background phosphorescence originating from filter paper substrates can interfere with the detection and quantitation of trace-level analytes. High-purity grades of HPMC were investigated as SSRTP substrates in an attempt to overcome this limitation. When compared directly to filter paper, HPMC allows the spectroscopist to achieve greater sensitivity, lower limits of detection (LOD), and lower limits of quantitation (LOQ) for certain phosphor/heavy-atom combinations since SSRTP signal intensities are stronger. For example, the determination of the analytical figures of merit for a naphthalene/sodium iodide/HPMC system resulted in a calibration sensitivity of 2.79, LOD of 4 ppm (3 ng), and LOQ of 14 ppm (11 ng). Corresponding investigations of a naphthalene/sodium iodide/filter paper system produced a calibration sensitivity of 0.326, LOD of 33 ppm (26 ng), and LOQ of 109 ppm (86 ng). Extended purging with dry- nitrogen gas yields improved sensitivities, lower LOD's, and lower LOQ's in HPMC matrices when LOD and LOQ are calculated according to the IUPAC guidelines. To test the universality of HPMC, qualitative SSRTP spectra were obtained for a wide variety of probe phosphors offering different molecular sizes, shapes, and chemical functionalities. Suitable spectra were obtained for the following model polycyclic aromatic hydrocarbons (PAHs): naphthalene, p-aminobenzoic acid, acenaphthene, phenanthrene, 2-naphthoic acid, 2-naphthol, salicylic acid, and triphenylene. Filter paper and HPMC substrates are inherently anisotropic, non-heterogeneous media. Since this deficiency cannot be addressed experimentally, a robust statistical method is examined for the detection of questionable SSRTP data points and the deletion of outlying observations. If discordant observations are discarded, relative standard deviations are typically reduced to less than 10% for most SSRTP data sets. Robust techniques for outlier identification are superior to traditional methods since they operate at a high level of efficiency and are immune to masking effects. The process of selecting a suitable sample support material often involves considerable trial-and-error on the part of the analyst. A mathematical model based on Hansen's cohesion parameter theory is developed to predict favorable phosphor-substrate attraction and interactions. The results of investigations using naphthalene as a probe phosphor and sodium iodide as an external heavy-atom enhancer support the cohesion parameter model. This document includes a thorough description of the fundamental principles of phosphorimetry and provides a detailed analysis of the theoretical and practical concerns associated with performing SSRTP. In order to better understand the properties of both filter paper and HPMC, a chapter is devoted to the discussion of the cellulose biopolymer. Experimental results and interpretations are presented and suggestions for future investigations are provided. Together, these results provide a framework that will support additional advancements in the field of solid-surface room-temperature phosphorescence spectroscopy.
- Doctoral Dissertations