ments become much more probable. We find that the abundance of the more specific data in a pure metastable spectrum makes possible many interesting correlations of these metastable reactions with the types of precursor ions and products involved. To illustrate this the n-decane data have been plotted in Figure 5 according to the mfe of the precursor and of the daughter ion of each of the monoisotopic transitions of Table I ; this display will be referred to as a metastable map, The ion abundances of the normal mass spectrum are shown on the axes, and the masses of the neutral products are indicated by the diagonals. Automatic preparation of a metastable map should be feasible using a computer-controlled plotter; the relative abundances of the ions could be indicated in a 3dimensional display similar to the topographical element map used for high resolution mass spectra (19). The odd-electron molecular ion, CnH2,+*+,decomposes to form the saturated alkyl ion, Cn-xH2n-sz+1A, or the C, - , H ~ , - Z ~ ~ ion by losses of, respectively, an alkyl radical (C,H2,-1.) or an alkane molecule (C,H2,+2). These transitions are abundant for the formation of the larger daughter ions. The alkyl ions are the most abundant type in the normal spectrum. These are involved as precursors in 18 of the metastable transitions, primarily cleaving to form another alkyl ion and a C,Hz, molecule. The alkyl ion tends to cleave in a nearly symmetrical fashion; the number of carbon atoms in the ion product is usually equal to or slightly larger than the number in the neutral molecule. The only other decompositions of the alkyl ions observed involve losses of Ht or CHI from relatively small alkyl ions. Most of the metastable transitions leading to daughter ions of higher masses (C4Hs’; or larger) involve the decomposition of odd-electron ions, except for the alkyl ions noted above. The most common precurso’r of this type is the C,Hz,t ion (olefin or cycloalkyl), decomposing by the loss of CH3. or CzHB to produce Cn-zH2n-2z--1+ ions, or by the loss of C2H4or C3Hs to produce a smaller Cn-,Hzn-2,T ion. AIthough nearly one third of the transitions observed are of these types, in general they do not produce metastable peaks in high abundance. The more abundant metastable transitions which produce the smaller fragment ions generally involve the loss of a small molecule, especially CPHI, CH4, and €32. This is not too surprising in view of the stability of these products, and the fact that in a cleavage producing a larger complementary (19) R. Venkataraghavan and F. W, McLafferty, ANAL.CHEM.,39, 278 (1967).
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ANALYTICAL CHEMISTRY
product, the charge retention would be less probable on the smaller fragment. As expected (20) almost all of the 31 transitions involving the decomposition of an even-electron ion yield another evenelectron ion and a molecule. The exceptions, C3H3+ C3H2’ and C2HSL--+ C2H2t,although of weak intensity, are surprising from our present knowledge of such reaction mechanisms. The advantages of high sensitivity, low ambiguity of identification, and amenability to automatic data-handling techniques suggest photoplate-recorded pure metastable spectra as a general method for the identification of metastable ion transitions.
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ACKNOWLEDGMENT
The authors are grateful to W. A. Henderson, American Cyanamid Co., for the sample of 2,3-dihydroxy-2,3-diphenylindanorie and to R. E. Peterson for photography. RECEIVED for review January 9, 1967. Accepted August 25, 1967. Work supported by National Institutes of Health (GM 12755). (20) F. W. McLafferty, “Mass Spectrometry of Organic Ions” Academic Press, New York, 1963, p. 309.
Correct ion Determination of Sodium in Ultrapure Silicon and Silicon Dioxide Films by Activation An a lysis In this article by James F. Osborne, Graydon B. Larrabee, and Victor Harrap [ANAL.CHEhI., 39, 1144 (1967)], on page 1148 the Acknowledgment and credit for financial support were inadvertently omitted. The authors express sincere thanks to H. G. Carlson and C. R. Fuller for many helpful suggestions and discussions. Thanks are also due to C. E. Jones for the ellipsometer measurements, The financial support of the Rome Air Development Center under Contracts AF 30(602)-3723, 3727 for part of this work is gratefully acknowledged.
