employed. Cadmium appeared to depress the silver emission slightly. Cobalt possesses weak lines a t 335.4, 336.8, 338.5, 338.8, and 339.5 mp, and a strong line a t 340.5 mp. The silver line a t 338.3 mp cannot be resolved from the cobalt lines; specificity factor is approximately 130 for a spectral band width of 0.14 mp (0.025 mm. slit width). At a slit width of 0.025 mm., the silver line a t 328.0 mp is not completely resolved from the copper line a t 327.4 mp. However, the peak of the silver line is separated sufficiently from the underlapping copper emission to permit its height to be determined. The correct silver reading is obtained when the base-line method of measuring the background a t 326 and a t 330 mp is used. Kickel possesses an emission line a t 338.1 mp; the specificity factor is approximately 5.
Calcium and tin increased the background readings about 40%. In this region tin possesses a series of weak molecular band systems. Whereas tin also definitely depressed the silver emission, calcium appeared to have little effect upon the silver readings. In the presence of calcium, the background is altered in the region of the silver line a t 328.0 mp and necessitates securing a background reading only a t 327 mp. Cerium enhanced slightly the silver readings but did not affect the background readings. Ammonium, chromium, magnesium, manganese, potassium, and zinc depressed slightly the silver emission. In each case, a slight increase in the background was observed, especially in the vicinity of the 338.3-mp silver line. The spectral and radiation interferences of the other cations investigated were negligible.
LITERATURE CITED
(1) Dean, J. A., “Flame Photometry,” Chap. 6, McGraw-Hill, New York,
1960. (2) Dean, J. A., Kuper, H. S., unpublished studies to be included in Ph.l). thesis of H. S. Kuper. (3) Foster, W. H., Hume, D. X., AXAL. CHEW31,2028 (1959). (4)Fuwa, K., Thiers, R. E., Vallee, B. L., Baker, M. R., Ibid., 31,2039 (1959). (5) Galloway, N. McK., Analyst 83, 373 f lCJ.58).
(6j Handley, T. H., Dean, J. -4., AXAL. CHEM.32,1878 (1960). ( 7 ) Pungor, E., Konkoly-Thege, I., dcta Chim. Acad. Sci. Huna. 13, 235 (1958). (8) Rathje, A. O., A ~ A L’ .CHEM. 27, 1583 (lCL5.5).
RECEIVED for review September 12, 1960. Accepted November 30, 1960. Taken in part from the M.S. thesis of C. B. Stubblefield at the University of Tennessee, June 1960.
Correlation of Mass Spectra with Structure in Aromatic Oxygenated Compounds Methyl Substituted Aromatic Acids and Aldehydes THOMAS ACZEL and H. E. LUMPKIN Manufacturing Department, Research and Development Division, Humble Oil & Refining
Co., Humble Division,
b The correlations existing between mass spectra and chemical structure are examined in detail for a group of aromatic acids and aldehydes. Particular emphasis is given to the study of ions which can b e used for analytical applications, as qualitative and quantitative determinations and prediction of sensitivities of compounds currently unavailable for calibration. As in the case of aromatic alcohols and phenols, discussed in a precedent publication, the results obtained in the present work confirm that the fragmentation pattern is greatly influenced by the position of the substituents on the benzenic ring.
Sources of the compounds used in this work were commercial, if available; otherwise, the compounds were prepared in these laboratories. A list of the coinmercial sources is given in the tables.
T
HE CORRELATIONS that can be established between mass spectra and chemical structure and the usefulness of their applications in analytical mass spectrometry have been discussed by several authors and for a number of chemical classes. Need for extending similar studies to new types of compounds lies in the immediate applicability of the results obtained to ordinary analytical work, and, eventually, to a better understanding of the
386
ANALYTICAL CHEMISTRY
multiple factors involved in the formation of ions under electron impact. I n a precedent paper ( I ) , we discussed the mass spectra of several aromatic alcohols and phenols. The present communication deals with the spectra of aromatic acids and aldehydes. Spectra of aromatic esters, as well as the considerations that might be applied to most of the compound types hitherto examined, will be discussed in a following communication. EXPERIMENTAL
The data reported were obtained on Consolidated Electrodynamics Corp. Models 21-102 and 21-103C mass spectrometers, and recorded either on an oscillograph or with the CEC peak digitizer (Mascot). Experimental conditions were comparable in every detail to that described in the previous work (1).
The availability of a solids inlet system (3) was particularly helpful in the case of the higher molecular weight acids, which could not be otherwise introduced into the mass spectrometer. Peak heights are expressed as per cent of the total ionization, calculated as the summation of the peak intensities from m/e 73 to m/e (parent 2) (1).
+
Baytown, Tex.
DISCUSSION OF SPECTRA
This study confirms that the respective position of the various substituents on the benzene ring has a leading importance in the formation of fragment ions. The so-called proximity effect, by Lumpdiscussed by McLafferty (4, kin and Nicholson ( 8 ) ) and in our previous communication ( I ) , is observed in a number of ions formed from the compounds discussed. Particularly remarkable is the regularity of this, and similar trends, in more complex types of substitution. Aromatic Acids. A number of aromatic acid spectra have recently been discussed by McLafferty and Gohlke ( 4 ) . Our data, though based on a larger quantity of compounds, confirm essentially the findings contained in their publication. For convenience, the spectra studied are divided into three main classes,
c
cy
+ n.
