Marvin Margoshes

An evaluation of the induction-coupled, radio-frequency plasma torch for atomic emission and atomic absorption spectrometry

Abstract A study has been made of the induction-coupled, 4.8 MHz, plasma torch as a source of atoms for emission and absorption spectrochemical analysis. The factors evaluated include sensitivity, limits of detection, inter-element effects, limitations, and general convenience. In agreement with other reports, the plasma torch was found to give useful emission signals for several elements which are difficult to excite in chemical flames, such as B, Ta, and Ti. The value of the source for atomic absorption spectrometry was found to depend on the availability of bright line sources. Pronounced inter-element effects were found, affecting particularly the emission signals. In most cases, these inter-element effects were enhancements of the emission, although in one case a suppression was observed. Except for a few refractory elements, the 4.8 MHz plasma torch does not appear to be a suitable replacement for the chemical flame.

Laser probe excitation in spectrochemical analysis.I: characteristics of the source.

A modified laser probe for spectrochemical analysis is described. A high energy laser beam is focused onto a specimen to vaporize a sample from a small area, and the vapor thus formed is further excited by a spark discharge. The characteristics of emission spectra with and without auxiliary spark excitation are compared. Spectrograph illuminating systems for qualitative and quantitative analysis were investigated. Some difficulties were encountered with the laser probe, and modifications were made to the instrument to alleviate some of these problems. Some typical analytical applications are discussed.

A pneumatic solution nebulization system producing dry aerosol for spectroscopy

Abstract An efficient sample introduction system was developed for atomic spectroscopy of aqueous solutions. It is made up of a pneumatic nebulizer, a heated chamber for solvent evaporation, and a chilled condenser for solvent removal. Features include low gas flow rate, high efficiency, and elimination of the solvent. Overall efficiency is 35 %.

Laser Probe Excitation in Spectrochemical Analysis. II: Investigation of Quantitative Aspects

A study has been made of quantitative analysis by a laser probe with spark excitation of the sample vapor. Random errors come largely from variations in laser energy and from photometric errors. The parameters of the spark circuit affect the line intensities; however, these factors are well controlled. Correlations have been established between the energy of the laser beam, the size of the pit formed, and spectral intensities. For most purposes, single-spike laser operation has been found to be preferable to multiple-spike operation. At present, the coefficients of variation for analysis are 15% to 40%.

Data acquisition and computation in spectrochemical analysis: a forecast

Abstract Some new applications of automation and computerization in emission spectrochemical analysis are proposed. Automated microphotometers now make it possible to digitize complete photographically-recorded emission spectra in a reasonable time. Television techniques offer the prospect of digitally recording complete spectra photoelectrically, circumventing the problems and loss of time encountered with photographic spectroscopy. Reduction of the data with computers should make possible completely automatic qualitative analysis. Semiquantitative analysis without standards may also be possible. When standards are available, the use of computers for data reduction should improve the accuracy of analysis by allowing complex corrections to be made for interelement effects. The cost of programming could delay the development of these proposals, and a cooperative research program is suggested to reduce the cost to any one laboratory.

Excitation and Ionization in Arc and Spark Spectroscopic Sources

The mathematical theories which are applicable to the excitation and ionization of atoms in plasmas at thermal equilibrium are described. These processes are controlled by the temperature and electron density in the plasma; some methods of determining these parameters are given. There have been several measurements of arc and spark temperatures in air, but few determinations of electron densities or of temperatures in gases other than air. It is shown that, even with the limited data available, the theories can be applied to practical problems which arise in spectrochemical analysis.

Application of digital computers in spectrochemical analysis—computational methods in photographic microphotometry

Abstract A new method of computation is described for calibration of photographic emulsions and conversion of microphotometer readings to relative intensities on a digital computer with special application to spectrochemical analysis. The method for emulsion calibration replaces graphical procedures by a numerical method which is well suited for digital computations. The method of computation and its underlying assumptions are described, and results are given of tests of the procedure. It is recognized that the entire experimental arrangement is being calibrated, not merely the photographic emulsion, and it is shown how malfunctions of the microphotometer which affect the calibration can be recognized from the output of the computer. The program for conversion of microphotometer readings to relative intensities provides for several alternate calculations, including selection of the proper calibration parameters according to the wavelength of the line when these data are supplied for more than one wavelength region, as well as correction for step and background where required. The program is written to provide for automatic selection of the required alternative calculation, based on a preliminary analysis of the input data.

Simple Arc Devices for Spectral Excitation in Controlled Atmospheres

The replacement of air around a carbon arc by other gases has been shown to have several effects in the excitation of spectra, the most obvious being the elimination of cyanogen bands when the atmosphere surrounding the arc contains no nitrogen. Although the effects of controlled atmospheres have been applied in spectrographic analysis, work along these lines has been limited by the practical difficulties involved. These difficulties include delays in changing electrodes between samples, the need for flushing the chamber before excitation can be started, and clouding of chamber windows by deposits of sample and electrode vapors.