(9) H. W. Drawin and P. Felenbok, "Data for Plasmas in Local Thermodynamic Equilibrium", Gauthier-Villars, Paris, 1965. (IO) D. E. Newbury, K. G. J. Heinrich, and R. L. Mydlebust, Proceedings of ASTM Symposium on Surface Analysis Techniques for Metallurgical Applications, Cleveland, Ohio, March, 1975, ASTM Special Technical Publication
596. (11) D. E. Newbury, National Bureau of Standards, Washington, D.C., personal communication, 1975. (12) P. Williams and C. A. Evans, Jr., in "Secondary Ion Mass Spectrometry", K. F. J. Heinrich and D. E. Newbury, Ed., NBS SP-427, U.S.G.P.O., Washington, D.C.. 1975,pp 63-68. (13)C. E. Moore, "Atomic Energy Levels", Vols. 1-111, NSRDS-NBS 35, U.S.G.P.O., Washington, D.C., 1971. (14)J. F. Lovering, in "Secondary Ion Mass Spectrometry", K. F. J. Heinrich andD. E. Newbury,Ed., NBSSP-427, U.S.G.P.O., Washington, D.C., 1975, pp 135-178. (15) M.J. Dresser, J. Appl. Phys., 39,338 (1968). (16)2. Jureia, Int. J. Mass Spectrom. /onPhys., 12, 33 (1973),and references therein.
(17)P. W. J. M. Boumans, "Theory of Spectrochemical Excitation", Plenum Press, New York, 1966,pp 78-80. (18)H. W. Drawin, in "Reactions under Plasma Conditions", M. Venugopalan, Ed., Vol. 1, Wiley, New York, 1971,pp 123-125. (19)G. Carter and J. S. Colligon, "Ion Bombardment of Solids", American Elsevier, New York, 1968,p 88. (20) R. F. K. Herzog, W. P. Poschenrieder, and F. G. Satkiewicz, Radiat. Eff., 18, 199 (1973). (21) G. Blaise and G. Slodzian. Surf. Scb, 40, 708 (1973).
RECEIVEDfor review January 12, 1976. Accepted April 26, 1976. This research was supported in part by the National Science Foundation under Grants DMR-72-03026 and MPS-74-05745.
Ana Iys is of Organic Mixtures Using Metastable Transition Spectra E. J. Gallegos Chevron Research Company, Richmond, Calif. 94802
Metastable transitions obtained by accelerating voltage scanning are used in the analysis for specific organic components in a mixture. This technique Is described and applled to the analysis of terpanes, steranes, and phthalates in complex organic mixtures. The results obtained using metastable transition spectra and normal mass spectra compare well with that obtalned by GC-MS.
This paper describes the use of metastable transition (MT) spectra in the analysis for specific organic components in a mixture. In many cases, this technique gives much of the same information obtained by single ion detection GC-MS, the advantage being that M T spectra are obtained in only a small fraction of the time required for GC-MS. M T analysis is based on the ability of a double-focusing mass spectrometer to detect specific ionic decomposition processes and identify products and related progenitors without interference from other reaction processes and their related ion participants. This, in effect, provides an isolation technique with a resulting capability similar to GC-MS. The experimental technique is described, and three examples of its application are given. These are terpane, sterane, and alkylphthalate analysis in complex organic mixtures. EXPERIMENTAL Metastable transitions in mass spectrometry were first reported by Hipple and Condon ( I ) in 1945. The theories of metastable transitions and the techniques of obtaining these kinds of data have been summarized recently (2,3 ) . This work was done on an MS-9 double focusing high resolution mass spectrometer.The instrument was modified so that the accelerating voltage can be scanned from 2-8 kV. The electrostatic sector voltage is held constant at 170 volts which, with an accelerating voltage of 2 kV, will produce normal mass spectra. The sample is introduced through an all-glass, hot inlet ( 4 ) or by using a direct insertion probe. The magnet is adjusted to a current which will bring into focus a daughter ion Mz+ of interest. The accelerating voltage is then scanned from 2-8 kV to produce the metastable transition spectra used in this
study. This arrangement will allow metastable transitions to be observed due to precursor ions MI+ with a mass up to four times that of the daughter ion Mz+. 1348
ANALYTICAL CHEMISTRY, VOL. 48, NO. 9, AUGUST 1976
RESULTS M T analysis is possible only if a decomposition process can be found that is uniquely characteristic of a compound or compound type. There are many systems which obey the requirements for M T analysis. Three examples of this are given. Terpanes and Steranes. Terpanes and steranes are two systems that fall well inside these requirements. Many terpanes, either pentacyclic- or tricyclic-saturated hydrocarbons found in nature, fragment on electron impact t o give a base peak at m / e 191 fragment ion ( 5 , 6 ) .See Figure 1.
Similarly, steranes which are saturated tetracyclic hydrocarbons fragment to give a base peak at mle 217 fragment ion. See Figure 2. Figures 3 and 4 show the metastable spectra of authentic cholestane, a C27 sterane, and authentic gammacerane, a C30 terpane, respectively. Each shows only one major metastable peak. In each case, it is due to decomposition of the molecular ion, M f , to give the characterizing fragment ion m/e 217 in the case of cholestane and m/e 191 in the case of gammacerane. The well-analyzed saturated fraction of the extractable portion of Green River shale (7) is used to demonstrate the use of the method. Figure 5 shows the metastable scan of m/e 191 of this fraction. The most important peaks are those due to C31, C30, and C29, followed by the C20 and C2l terpanes. Similarly, Figure 6 shows the metastable results for a scan of m / e 217. These results show that the largest metastable peak is due to a C29 sterane followed by the C28 and, finally, C27 steranes. The normal mass spectrum was used to calculate the total concentration of terpanes and steranes in this sample. This is done in the following manner. The mle 191 fragment ion measured 2.33% of the total ionization of the saturate fraction of Green River shale. This fragment ion represents one eighth of the total ionization in the mass spectrum of the average terpane in this sample so that the total terpane contribution to the total ionization of the sample is 18.6%. The m / e 217 fragment ion measured 1.25% of the total
Table I. Comparison of GC-MS and MTA Results of Terpanes and Steranes in the Saturate Portion of Green River Shale
>[@l+
MTA
GC-MS Terpanes mle 191
1.0
c30 c29 c21
13.6 2.3
1.1 13.2
2.2 0.4
c20
0.4 1.4
Total
18.7
18.6
c29
10.3
10.1
C28
1.6 1.9
6.3 1.8 0.6
19.8
18.8
Te rpaner
Flgure 1. Main fragmentation path of a tri- and pentacyclic terpane
c31
1.7
Steranes
c27
...
c22
Total
mle 217
Steranes
Figure 2. Main fragmentation path of a C27 sterane
Table 11. Comparison of GC-MS and MTA Results of Terpanes and Steranes in the Saturate Cut from the Pyrolysis Oil from Green River Shale
mle 217
Percent
GC-MS
Sterane
MTA
Terpanes c3l
6.5
1.3
c30 c29
2.0
2.0 2.0
C28 c27
2.0 0.2 2.4
Total
7.1
0.9
1.5 7.7
Sterane 0.1 0.5
c27
0.8 0.6 0.3
Total
1.7
1.4
c29
Figure 3. Metastable spectrum of m / e 217 of cholestane
CI1
mleY 191
@-[*I+ Terpane
I
I
.I
d i l
C28
0.2
r9
C,. rnle 191
\
i A
-
-____
\-+,I,A
-
I
.
'
:\
-- I
rric-
