Thomas J. Vickers
Florida State University
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Featured researches published by Thomas J. Vickers.
Applied Spectroscopy | 1992
Chao Wang; Thomas J. Vickers; Joseph B. Schlenoff; Charles K. Mann
The feasibility of a direct quantitative analysis of styrene by Raman spectroscopy during an emulsion polymerization is examined. A dispersive spectrometer fitted with an intensified diode array detector is used with excitation from the 514.5-nm line of an Ar-ion laser. The limits of detection are 0.26 weight percent styrene in the reaction mixture. Raman measurements are compared with those obtained by UV absorption measurements on extracted samples and found to give essentially the same results.
Spectrochimica Acta Part B: Atomic Spectroscopy | 1973
Kenneth W. Busch; Thomas J. Vickers
Abstract Experimental measurements of the spectroscopic temperature and the electron temperature in low-pressure rare gas plasmas sustained by a microwave generator operating at 2450 MHz have revealed divergent values. These measurements have been interpreted on the basis of a radiative recombination model originally proposed by Schluter. The importance of Penning ionization by metastable rare gas atoms in the excitation of foreign atoms has been discussed in terms of this model. On the basis of the radiative recombination model for these plasmas, the parameters of analytical importance are the concentration and energy of electrons in a high energy electron group, the concentration and energy of electrons in a low energy electron group, and the concentration of metastable rare gas atoms. Measurements of the spectroscopic temperature of an argon plasma have revealed that the energy of electrons in the low energy electron group is not greatly affected by applied microwave power and pressure over the range from 1–25 torr. The energy of electrons in the high energy electron group is not greatly affected by pressure and applied microwave power over the range studied, but has been shown to depend on the ionization potential of the plasma gas. The total electron concentration is not greatly affected by gas pressure for low applied powers, but varies with applied power, particularly at low pressures. The concentration of metastable argon atoms has been shown to depend on both the applied power and pressure. Studies of the excitation of mercury by these plasmas have led to results which are consistent with the radiative recombination model.
Vibrational Spectroscopy | 1992
Chan Kong Chong; Chengbo Shen; Yoke Fong; Jianxiong Zhu; Feng-Xia Yan; Sabitra Brush; Charles K. Mann; Thomas J. Vickers
Abstract Considerations affecting the use of fiber-optic components in Raman measurements for quantitative analysis are described. Bidirectional single-fiber probe systems and a unidirectional multi-fiber probe are compared. Results are given for a system employing a 1 × 6 bifurcated probe. In situ monitoring of a reaction for formation of a conducting polymer, polypyrrole, is described. A spatial averaging advantage for the fiber-optic system in measurements on solid samples is described, and results for some purine and pyrimidine mixtures are reported.
Journal of Pharmaceutical and Biomedical Analysis | 1997
Chao Wang; Thomas J. Vickers; Charles K. Mann
A comparison was made between Raman and high-performance liquid chromatography (HPLC) analysis of aspirin tablets. The basis was an assay of aspirin content and the determination of salicylic acid produced by decomposition. Raman observations were performed directly on both intact and powdered tablet material. The limit of detection of HPLC with an ultraviolet detector is lower than that of the Raman measurement, but both are adequate for this application. The reproducibility of the Raman measurement is somewhat better than that of the HPLC measurement. Both methods were used in a degradation study in which samples were stored in a humid atmosphere for a maximum period of 8 weeks. Aside from somewhat higher salicylic acid responses from the HPLC method, which were attributed to hydrolysis during chromatography, results from the two methods were comparable. Direct Raman measurements are faster and do not require the use of solvents.
Applied Spectroscopy | 1977
Christopher D. Keirs; Thomas J. Vickers
The development of plasma arc devices as replacements for chemical combustion flames in trace element analyses by emission spectrometry is traced with particular emphasis on those devices in which the spectrometric observation is made in the non-current-carrying portion of the discharge or “plume.” The question of local thermal equilibrium in both the arc column and plasma plume is discussed and the dependence of temperature on experimental variables is considered in terms of a model. In addition to the temperature attained, the performance of various gas stabilized arcs and plasma jets is discussed with reference to interferences, background emission, limits of detection, and precision. Particular attention is paid to the problem of sample aerosol introduction into the high temperature plasma. The dc plasma arc at its present level of development is compared with the inductively coupled plasma for use as a source in emission spectroscopy.
Applied Spectroscopy | 2001
Thomas J. Vickers; Ronald E. Wambles; Charles K. Mann
A study has been made of the use of polynomial curve fitting for removal of nonlinear background and high-spatial-frequency noise components from Raman spectra. Two variations on polynomial curve fitting through a least-squares calculation are used. One, involving fitting data x values to corresponding y values, was used to approximate background functions, which are subtracted from the original data. For smoothing, a reference matrix of six vectors that contains a unity d.c. level, a ramp made up of x values, a quadratic made up of x2 values, etc., is fitted to a section of data. The reference vectors are scaled by the fit values and added to give the smoothed estimate of a spectral peak. It is demonstrated, with factor analysis as a test procedure, that the background removal procedure does remove nonlinearities that were present in the original data. The smoothing procedure rejects high-spatial-frequency noise without introducing detectable nonlinearities.
Applied Spectroscopy | 1993
Chao Wang; Thomas J. Vickers; Charles K. Mann
Direct analysis of the organic phase of an emulsion polymerization is described. Quantification uses the bending mode peak of water, which makes up the bulk of the reaction medium, as an internal standard. Although demonstrated with methyl methacrylate, the process is generally applicable to emulsion polymerizations. It does not require the introduction of an extraneous internal standard component into the reaction mixture.
Applied Spectroscopy | 1993
Ching-Hui Tseng; Joseph F. Ford; Charles K. Mann; Thomas J. Vickers
A readily automated procedure for wavelength calibration of multichannel spectrometers is described. Once applied, line positions can be read from the multichannel display with good accuracy and precision for any spectrometer setting. The procedure uses Ne atomic lines as wavelength standards. A novel apodization procedure is used for accurate measurement of the pixel positions of the neon lines. Raman line positions can be determined with an average error of less than 0.2 cm−1.
Applied Spectroscopy | 2002
Hsiaoling Wang; Charles K. Mann; Thomas J. Vickers
The effect of particle size on Raman intensity has been measured for a number of crystalline solids with a fiber-optic-based Raman spectrometer. Particle sizes ranged from 76 to 605 μm. Materials examined were sodium nitrate, sodium chlorate, sodium bromate, potassium ferrocyanide, potassium ferricyanide, and copper(II) sulfate. Raman intensity was found to decrease with increasing particle size. The factors responsible for this trend are discussed. We conclude that the major factor is diffuse reflectance that enhances the overlap between the excitation and collection beams. The depth of sample contributing to the Raman signal has been examined for both powders and tablets as a function of powder particle size. Materials examined in this study were sodium nitrate, sodium sulfate, sodium chlorate, sodium bromate, potassium ferrocyanide, potassium ferricyanide, and copper(II) sulfate. For nonabsorbing powders, the depth of sample contributing to the signal exceeded 15 mm. The effect of the pressure used in forming tablets on the Raman signal strength and reproducibility has been examined for sodium nitrate. The Raman intensity was found to decrease with increasing pressure until a tablet of constant density was formed. The effect of particle size and particle size mismatch on the sodium nitrate Raman signal in binary mixtures with potassium chloride, potassium bromide, and potassium iodide has been examined. Good reproducibility was found to require matching of component particle sizes.
Applied Spectroscopy | 1994
Daniel R. Lombardi; Chao Wang; Bin Sun; Augustus W. Fountain; Thomas J. Vickers; Charles K. Mann; Frederich R. Reich; James G. Douglas; Beverly A. Crawford; Frank L. Kohlasch
Raman spectra have been measured for a number of nitrates, nitrites, sulfates, ferrocyanides, and ferricyanides, both in the solid phase and in aqueous solution. Accurate locations of peak maxima are given. Limits of detection for some of the compounds are given for solutions and for solid mixtures in NaNO3. Preliminary measurements have been made on core material recovered from the storage tanks on the Hanford site in Richland, Washington. Representative spectra are presented, showing that it is possible to observe responses of individual components from measurements made directly on untreated cores, with the use of a fiberoptic sampling probe.