Fourier transform spectrometry in the ultraviolet-visible region.

摘要

An investigation of the analytical merits of Fourier transform spectrometry, at short wavelengths, was made using a Michelson interferometer capable of operation in the ultraviolet-visible region (UV-Vis). The multiplex effect on signal-to-noise ratio was examined. Advantages and disadvantages of Fourier transform spectrometry in the UV-Vis relative to conventional spectrometry are discussed.;A review of the use of the Michelson interferometer for spectroscopic purposes and for Fourier transform spectrometry is presented. The interferometers currently available for operation in the UV-Vis are described.;Molecular absorption measurements were made using an interferometer and a diffraction grating. This approach did not have significant advantages over conventional methods and the multiplex disadvantage degraded signal-to-noise ratio. Detection limits are given for some polycyclic aromatic compounds (PAC).;Molecular fluorescence measurements of PAC frozen in a Shpol'skii solvent at 77K were performed by Fourier transform spectrometry. Emission spectra were acquired by using a monochromator to select the excitation radiation and a cutoff filter after the interferometer. Excitation spectra were acquired by passing broad-band, ultraviolet radiation through the Michelson interferometer onto the frozen sample. The detection limits from the emission spectra were sufficiently poor to prohibit analytical use. Detection limits obtained from the excitation spectra were comparable to conventional methods, in some cases even better, due to the use of broad-band excitation.;A Fourier transform spectrometer for continuum-source, atomic absorption measurements was constructed and evaluated. Degradation of signal-to-noise ratio due to the multiplex effect was reduced by using a grating for dispersion of the radiation before the interferometer. Continuum radiation passed through a flame containing the analyte. A 5 nm window of radiation, centered around the absorption lines of interest, was collected and passed through the interferometer onto a photomultiplier tube. Detection limits using the interferometer were poorer than conventional measurements, but a few advantages were realized. Complete absorption line profiles were acquired, including measurements of the true background in the region of absorption. Calibration curves were extended by using the line profile. Wavenumber accuracy was high and spectral resolving power could be easily modified.