Edwin S. Hodge

The Spectrochemical Analysis of Solutions. A Comparison of Five Techniques

The spectrochemical analysis of solutions offers such a variety of advantages that a number of techniques have been developed and reported in the literature. There has been little or no intercomparison of the procedures or excitations, so it has been difficult to select one technique in preference to another. This paper describes studies of five different solution techniques and three excitation conditions A number of observations are reported regarding general conditions to give the best sensitivity and reproducibility. The effects of hydrochloric, nitric, sulfuric, and phosphoric acid on the spectra were also studied. The repression effects which were noted for some acids varied with the technique, acid concentration, and excitation potential of the line

A Rapid Matching Technique for Semi-Quantitative Spectrochemical Analysis:

Several widely-used methods of qualitative and semi-quantitative analysis involve the visual estimation of line intensity. The subjective nature of such observations and the repetitious handling of plates or films have led to the development of a visual intensity scale. A selected single line at several different intensities was enlarged to make a transparent intensity scale. This was placed behind the viewing screen of an ARL projection-comparator A table of intensities measured by the scale was prepared for about 40 elements ranging from 0.0001 to 30% concentration. Using the scale and the table, over 90% of the individual determinations on 25 standard samples were in agreement with the certified values. The advantages of this technique include faster analysis, freedom from handling standard spectrograms on plates or films, elimination of eye strain in using a plate magnifier, and the elimination of comparison of lines intensities by memory.

David Alter and other spectroscopists in Western Pennsylvania

The work of a few lesser known American spectroscopists in Western Pennsylvania is briefly reviewed in this paper that is based on a talk given at the Bicentennial Symposium on Analytical Chemistry and Applied Spectroscopy held during the 1976 Pittsburgh Conference.

Working Curve Shifter

Some laboratories performing a variety of analyses do not find it convenient to prepare working scales for quantitative analysis but prefer to use working curves drawn up as needed or already on file. A curve shifter has been devised and found to be useful for several reasons. Working curves are drawn on conventional log-log co-ordinate paper and traced on to a transparent matte, shifting it horizontally when necessary to avoid confusing overlaps where curves may naturally fall close together. The use of the curve shifter is based on the hypothesis that working curves do not change in slope but may shift in horizontal displacement with changes in working conditions of excitation, photographic processing, or some other factors. Corrections for working curve shifts can be made easily and quickly.

Extraneous Element Effects as Shown by Data from Harvey's Semi-Quantitative Spectrographic Analysis

Harvey has listed the sensitivities for a large number of lines in a graphite base. Similar data are also given for many lines where a large amount of a single base element is present in addition to carbon powder.

Technique for Photographic Emulsion Calibration: Intensity Factor Tables

Nearly all modern methods of quantitative spectro-chemical analysis are based on the measurement of relative spectral intensities. For photographic procedures this is frequently done with an emulsion calibration curve. Two widely used methods for obtaining such a relationship include the preparation of a preliminary curve. In using such a procedure as the stepped-filter method, weakened and unweakened steps of the same line are read on the densitometer. Such readings are taken for 15-30 lines within a limited wavelength region covering the entire density range.

Selected Iron Lines on Commercial Spectrographs for Emulsion Calibration

The attached tables present some results reported in a paper by the above title at the Symposium on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pennsylvania, March 7, 1951. These tables represent homologous groups, each group having a lower energy level common to all the lines within itself. The data has been taken in part from Crosswhite (1). The values of I or log I may be plotted against the %T or density for these individual lines to obtain characteristic curves with a minimum of effort and time in plotting. The column headed quality lists a grade given by Crosswhite. Lines rated A,B, or C are most suitable, while lines rated as D may have from 10-30% self reversal, or some wavelength interference. Column headed resolution indicates the authors observations on spectrograms from a variety of commercial domestic instruments. Spectrograms from grating instruments having a dispersion from 7-3.5A per ram. were observed as well as those from the Bausch and Lomb Littrow Quartz Spectrograph and the Gaertner Two lens Spectrograph (type L254). The results were sufficiently similar so that they have not been tabulated individually, but as two groups, gratings and prisms. Lines marked I are suitably resolved and free from background when the exposure is sufficient to measure satisfactorily the densest line in the table. Rating 2 indicates that the line is probably suitable, but its use will depend upon the particular conditions used, quality of focus, slit width, etc. A rating of 3 indicates the line is not suitable for use due to wavelength interference.