Applications of time-resolved spectroscopy to spectrochemical analysis
Access full-text files
Date
1966
Authors
Burnett, Harold Morris, 1928-
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Department
Description
A study of several spark techniques of spectrochemical analysis was made using time-resolution as the basis for correlations. Particular emphasis was placed on improving the limits of detection attainable with the graphite spark technique, as well as procedures using metal electrodes. Rotating devices, mirror and disk, were used to trigger a spark source precisely and produce the time-resolved spectra. The light emitted from the sample materials was observed from the time of initiation of the discharge to the diminution of the afterglow light which was greater than 100 microseconds in some applications. The precisely triggered source permitted the superposition of many discharges which singly did not produce enough light for photographic recording. Line-to-background intensity ratios for total light and time-resolved exposures were used to establish the effects of the gaseous atmosphere, electrode sample composition, pressure, and various source parameters. The behavior of the element line intensities, background intensities, and the line-to-background intensity ratios showed the advantages of time-resolution techniques. Excitation of samples was carried out under controlled atmosphere conditions which were generally free of nitrogen to eliminate cyanogen formation. Excitation in binary mixtures containing oxygen showed the effect of oxygen on the sample volatilization behavior and the intensity of background radiation. Absolute sensitivities from 10⁻⁸ to 10⁻¹⁰ grams were obtained for several elements which were coated as residues on the surface of graphite electrodes, excited in an argon atmosphere, time-sectored to prevent the first 10 to 20 microseconds of radiation from reaching the spectrograph, and recorded photographically. Using time resolution, improvements in sensitivity of greater than an order of magnitude were found for cases of spark excitation where the line intensity was not easily measurable in total light exposures because of high background intensity. The studies were made using a uni-directional discharge and the traditional oscillatory discharge. Examples are given of the types of information to be derived from rotating mirror and rotating disk exposures, the advantages and disadvantages of each for testing and developing a spectrochemical procedure using spark excitation