Date of Award

4-3-1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

David C. Tilotta

Abstract

An electrothermal furnace, and a flow-cell were constructed to heat gas or liquid samples, respectively, to 200-400$\sp\circ$C in order to observe their near-infrared (NIR) emissions. In conjunction with the fountain or the flow-cell, a 1/8 m Ebert monochromator and an uncooled PbS detector were shown to be sufficiently sensitive for recording the NIR fingerprints of CH$\sb4$, N$\sb2$O, C$\sb2$H$\sb6$, CO$\sb2$ H$\sb2$O, and C$\sb2$H$\sb5$OH. At a temperature of approximately 400$\sp\circ$C, the molecular emission was confined to the long wavelength NIR region (1600-2500 nm) and yields gas limits of detection in the range of 4-10% V/V (3-10 mg/sec). Liquid detection limits for ethanol and water were determined at 3% and 60 ml/min, respectively. Reproducibilities, for the gas and liquid analytes were found to have RSDs of 3.0%, and the linear dynamic ranges of calibration were small (factors of 2-10).Spectral subtraction and derivative spectroscopy were evaluated as data handling techniques for NIR molecular emission of liquids. Spectral subtraction was found to be the most useful data handling technique examined. Spectral subtraction was used in extracting the ethanol spectrum from spectra of a mixture of ethanol and water.The emission spectrum from a natural gas flame yielded a spectrum with many sharp lines due to the rotational fine structure of the vibrational bands of water. These lines can be used to calibrate a NIR emission spectrophotometer. The emission from the natural gas flame was intense enough to give moderate (4 cm$\sp{-1}$) resolution, which was sufficient for most molecular spectroscopic work in the NIR region. Also, it was demonstrated that the emission from natural gas flames could be used for instruments with lower resolution (approximately 27 nm).

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