peaks shown on the TIM trace. Shaded TIM peaks are those which required a more complete identification. In order to do this, complete mass spectra were obtained on these and other GC peaks shown in the TIM trace. The detailed peak identifications are shown in Figure 3 and Table I. Each measurable peak is identified as to name or compound type. Exact identification and/or molecular weight, where indicated. have been obtained from complete mass spectra analysis and standard gas chromatographic retention times. Many of the smaller and/or unresolved peaks are only identified as to compound type from the mass chromatograms. This analysis establishes the identification of 1,3-butadiene, isobutene, 1-butene, and the likely position of 1butyne, 1,4-pentadiene, cyclopentadiene. cis-1,3-pentadiene, cyclopentane. and 2-methyl-1,3-pentadiene.Starting with Peak 55, Figure 3, there are several unknown peaks whose mass chromatograms indicate their molecular type to be 2 = -2. The most probable molecular assignments for these peaks would be either diolefins or cyclomonoolefins. The liquid volume per cent represented by the sum of these peaks is less than 1% of the pyronaphtha.
Dicyclopentadiene was positively identified for the first time in this kind of sample. This component has a parent ion a t mle 132 and a fragment ion a t mle 66. In addition, cross dimers between cyclopentadiene and methyl cyclopentadiene were observed. These compounds show parent ions a t mle 146 and tell-tale dimer fragment ions a t m / e 80. Several Cs vinyl aromatics were also identified including a-methylstyrene and the three vinyl toluenes. The related compounds, indane and indene, were also found in the heavy ends of the pyronaphtha. The ability to obtain complete mass spectra not only allows the identification of new components in this sample but also demonstrates the validity of hydrocarbon type identification using the powerful and rapid mass chromatographic technique. The detailed results of the MC and GC-MS runs were used to provide qualitative identifications for routine HRCGC. The HRCGC analysis was carried out on a similar but somewhat higher resolution 1000-ft by 0.02-in. squalanecoated capillary. HRCGC was then used to follow the effects of processing variables. Received for review ,June 20, 1973. Accepted .July 23, 1973.
lsobutane Chemical Ionization Mass Spectra of Volatile Lanthanide Chelates T. H. Risby, P. C. Jurs, and F. W. Lampe Department of Chemistry, The Pennsylvania State University, University Park, Pa. 76802
A. L. Yergey Scientific Research Instruments Corporation, 6 7 0 7 Whitestone Road, Baltimore, Md. 21207
The separation and analysis of the lanthanide elements pose many problems because of their similar chemical and physical properties. Among the various procedures which have been used to separate and purify these elements are fractional crystallization, liquid-liquid extraction, and ion exchange. All these procedures are extremely complicated. Classical chemical techniques for the qualitative and quantitative analysis of the lanthanides are even more difficult because of their chemical similarity. Emission, absorption, and fluorescent measurements in the X-ray, ultraviolet, or visible region of the electromagnetic spectrum are all very complicated, and often it is found that many of the lines and bands of the lanthanides overlap each other. This overlapping of peaks makes selective identification very difficult and often impossible. Also, these metals form stable diatomic monoxide molecules in flames (refractory oxides), a fact which makes analytical flame spectrometric methods almost impossible. In recent years, there has been considerable interest in the use of gas-liquid chromatography and a number of chelates have been found which exhibit thermal stability and volatility. In the course of this work, various chelates of the lanthanide elements were found which can be chromatographed successfully-notably the chelates based on the ligands 1,1.1,2,2.3,3-heptafluoro-’i,’i-dimethyloctane4,6-dione H(fod) and 2,2,6,6-tetramethyl heptane-3.5dione H(thd) (1-7). The lanthanide chelates unfortunately have not so far been successfully resolved completely by gas-liquid chromatography.
These volatile chelates have also been analyzed by electron ionization mass spectrometry uia the direct insertion probe (8-13). However, the results of these studies, although they are useful in terms of the analysis of individual lanthanides, are not very useful when mixtures of the lanthanide elements are to be examined. This is due to the fact that the fragmentation of the chelate is complex, and together with isotopic peaks these fragments often obscure peaks due to other lanthanide elements. A typical fragmentation before the mass spectrum becomes too complicated is as follows (13):
K. J. Eisentraut and R . E. Sievers, J . Amer. Chem. SOC..87, 5254 (1965). C. S. Springer, D. W. Meek, and R. E. Sievers, / n o r g . Chem.. 6 , 1105 (1967). T. Shigematsu, M. Matsui, and I . Utsumomiya, B u / / . Chem. SOC. Jap., 42, 1278 (1969). W . C . Butts and C. V. Banks, Ana/. Chem.. 42, 133 (1970). J. W. Mitcheil and C . V. Banks, Anai. Chim. Acta. 57, 415 (1971) C . A . Burgett and J. S. Fritz, Anal. Chem.. 44, 1738 (1972). R. F Sieck and C. V.Banks, Anal. Chem.. 44, 2307 (1972). R. J. Mayer, Sci. Toois, 15, 11 (1968). R. Belcher, R. J. Mayer, R. Perry. and W. I . Stephens, Ana/. Chim. Acta, 43, 451 (1968). J. D. McDonald and .J. L. Margrave, J. Less Common Metals. 14, 236, (1968) R. Belcher, I?. J. Mayer. R. Perry. and W. I . Stephens, J. Inorg. Nucl. Chem. 31, 471 (1969). 8. Kowalski, T. L. Isenhour. and R . E. Sievers, Ana/. Chem.. 41, 998 (1969). T. H. Risby and T. L. Isenhour, unpublished data.
A N A L Y T I C A L CHEMISTRY, VOL. 4 6 , NO. 1, J A N U A R Y 1 9 7 4
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weight of the sample molecule. Thus, one could expect to find an intense [M(thd)3 H]+ peak with little concurrent fragmentation. A typical chemical ionization system is shown: C,H,, eC3H,+ 2eCH,
0
+
- 15 - 43 - 57
-- + -
+
-71 -85 - 185
CJH7+
The extensive fragmentation by the use of electron ionization mass spectrometry, although useful in many cases for the determination of the structure of the compound, is undesirable when mixtures of compounds are to be identified. Chemical ionization (CI) mass spectrometry produces mass spectra of compounds in which ions from the molecules of interest are formed by ion molecule reactions ( 1 4 ) . This technique has the advantage that relatively little fragmentation takes place, especially if isobutane is used as the reagent gas. The major peak in many CI mass spectra appears one amu higher than the molecular (14) M. S. Burnaby Munson and F. H. Field, d . Amer. Chem. Soc.. 88, 2621 (1966).
C,H,+
+ C,H,,
C,H,+
reagent ion
+
+ + C,H,
M
C,Hs
+ MH'
sample Two excellent review articles (15, 16) discuss the fundamentals of CI mass spectrometry in detail. This technique has already found considerable application especially for the analysis of drugs and drug mixtures which by electron ionization mass spectrometry is extremely complicated (17). Chemical ionization mass spectrometry was chosen to investigate the lanthanide chelates because the spectra (15) F. H . Field. Accounts Chem. Res.. 1, 42 (1968). (16) M. S. Burnaby Munson, Anal. Chem., 43, (13), 28A (1971). (171 G. W. A. Milne. H. M . Fales. and T. Axenrod, Ana/. Chem., 43, 1815 (1971).
Table I. Calculated Relative Peak Intensities for M(thd)3 m e
La
Pr
Nd
Sm
Eu
Gd
Tb
DY
Ho
Er
Tm
Yb
LU
688 689 690 69 1 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 71 0 71 1 712 713 714 71 5 716 71 7 71 8 719 720 72 1 722 723 724 725 726 727 728 729
0.6 67.6 25.4 5.5 0.9
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...
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...
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...
...
...
...
...
... ...
...
. . .
... 18.4 15.2 20.8 12.7 15.3 5.1 4.9 1.6 4.1 1.5 0.3 0.1
...
...
68.0 25.6 5.5 0.9 ... ...
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162
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o
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... 2.1 0.8 0.2 10.2 11.5 13.1 9.3 2.8 18.7 6.9 16.9 6.0 1.3 0.2 ...
... ... ... ... ...
... .,. ... .. , .,,
... ... ... ... ... ... ... ...
. . . . . . .
...
...
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. . . .
.. , 32.5 12.2 38.1 13.8 2.9 0.5 ..,
...
, . .
...
... ... ... ... ...
... ... ...
... ... ...
0.1 0.1 1.5 10.6 17.8 16.7 22.2 7.4 16.4 5.8 1.2 0.2
.. .. .. .. .. .. ..
...
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. . . .
. . . .
...
...
...
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...
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...
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...
0.1 ...
... ,..
... ...
... ...
...
1.6 13.4 22.3 24.6 27.1 8.8 1.8 0.3
... ... ... ...
...
... ...
...
...
...
...
...
0.1
...
...
...
...
...
...
1.1 0.4 22.8 24.2 26.1 8.5 11.8 4.1 0.8 0.1 ...
... ...
... ...
...
...
...
... ...
...
, . .
...
...
68.0 25.6 5.5 0.9
...
..
...
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... ... ... ... ...
... ...
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.
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ANALYTICAL CHEMISTRY, VOL. 46, NO. 1, J A N U A R Y 1974
..
...
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.
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, . .
. . . ...
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... ...
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. . . .
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...
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...
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68.0 25.6 5.5 0.9
... ... ...
... ... ... ... ... ...
.
.
...
. . . .
.. .. .. ..
... ... ... ...
...
... ... . . . ... 68.0 25.6 5.5 0.9 . . . ... ... , . .
...
... ...
...
... ...
. . .
...
, . .
...
, . .
...
, . .
...
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0.1 ... 2.1 10.5 18.7 17.4 27.1 9.2 10.6 3.5 0.7 0.1
, . . , . . , . .
, . .
... ... ... 66.2 26.7 6.1 1.0
...
are expected to be simpler than those produced by elecelec tron ionization. Isobutane was chosen to provide essentialessential ly one ionic species per chelate. The mass spectra ohot bot tained hy the use of chemical ionization will make both el qualitative and quantitative analysis of the lanthanide elI ements simpler. Another reason for this choice is that if su( chemical ionization mass spectrometry proves to he sucwhos cessful for the identification of similar compounds whose ideal1 isotopes often overlap each other, then it will be ideally suited for the analysis of other metals which do not suffer suffe from isotopic problems.
EXPERIMENTAL Chelate Preparation. The lanthanide tris-2,2,6,6-tetrameth~ tris-2,2,6,6-tetramethyl ha heptane-3,5-dionates were prepared by the procedure which has Figure 1. isobutane chemical ionization mass spectrum of been. previously described (is). The lanthanide nitrates were wer . . . . . . . . . . . Eu(thd), reacted with the ligands in ethanol under an inert atmosphere, The products were precipitated and were purified by vacuum sublimation. Electron Impact (EI) Mass Spectrometer. The E1 mass spectra were run on an Associated Electronics Industries MS-902 double focusing mass spectrometer operating at low resolution. The ionization source was run at 140 'C, the accelerating potential was 6 kV, and the ionizing voltage IO eV. The samples were introduced into the ionization source on the direct insertion probe. Chemical Ionization (CI) Mass Spectrometer. The chemical ionization mass spectra taken during this research were run on a Scientific Research Instruments Corporation DRUGSPECT System. The system consists of a chemical ionization source, a quadrupole mass analyzer, and particle multiplier and electrometer detection system. The spectra were run with isobutane at I Torr as the reagent gas. Differential pumping allowed the remainder of Figure 2. Electron impact mass spectrum of Eu(thd)s the ionization section outside the actual ionization volume to be kept at approximately loe4 Ton and the analyzer section at approximately 5 x Torr. The samples were introduced into the ionization region with a direct insertion probe. The spectra were viewed on a Tektronix Oscilloscope, and permanent copies were recorded on a Honeywell 1508B strip chart recorder. To ohtain the CI mass spectra, 2 rl of solution approximately 2 parts per thousand (by weight, in terms of the lanthanide in henzene) was evaporated on the direct insertion probe. The temperature of the ionization source was varied between 150 "C for the more volatile chelates to 180"C for the less volatile ones.
RESULTS AND DISCUSSION In order to interpret the chemical ionization mass spectra obtained, a calculation summarized in Table I was performed. The calculated relative peak intensities expected for each of the thirteen lanthanide chelates are shown. The nominal mJe positions of the peaks reflect the fact that the chelates contain three ligands (549 amu), the metal atom, and one extra hydrogen. Thus, 57La138(thd)s produces an ion of mass I39 549 1 = 689 for the case where there are no C13, H2, or 0ls atoms in the ligands. Table I contains all contributions due to C13, H2, and 0 1 8 atoms in the ligands. For each isotope of each lanthanide, the following contributions were included: If the isotope with ligands containing no C13, H2, or 0ls yields a peak of mass M, then the (M 1) peak is due to the presence of (a) one H2, or (h) one C'3 atom; the (M + 2) peak is due to (a) two C13, or (h) one 0l8,or (c) two HZ, or (d) one H2and one C13; the (M+ 3) peak is due to (a) three C13, or (b) one 0ls and one H2, or (c) one 0 1 8 and one C13, or (d) two 0 3 and one N2,or (e) two H2and one U s , or (f) three H2 atoms. The contributions to the intensity in a particular mass position have been summed over all the isotopes of each lanthanide, and the total ion current for each spectrum set equal to 10090. As shown in Table I, even the monoisotopic lanthanides such as Pr are expected to give rise to one large peak, one intermediate peak, and one small peak. The lanthanides with many
+
+
+
(18)
K. J. Eisentraut and R. E. Sievers, (1965).
J. Arne,. Chem. Soc.. 87, 5254
Figure 3. lsobutane chemical ionization mass spectrum of Yb(thd)s isotopes such as Yb give a large number of relatively smaller peaks. The CI mass spectra were taken for all thirteen lanthanide chelates, and the mass spectra obtained were in every case consistent with the calculated intensities shown in Table I. Figure 1 shows the CI mass spectrum of Euithd),. Eu= 47.82% and Eul53 = ropium has two isotopes: 52.18% abundant. The spectrum clearly shows. the larger peaks and two smaller peaks expected. The spectrum is shown down to m l e 600, and there are no fragment peaks in this region. By contrast, Figure 2 shows the E1 mass spectrum of E u i t h d ) ~The . isotopic abundances of Eu are clearly seen; however, the spectrum displays a number of fragment peaks. It is not nearly as simple as the CI spectrum. It should be emphasized that the spectra were obtained on two different mass spectrometers with inherently different signal to noise ratios. As a result, the spectra show only these differences and not the signal-to-noise ratio of CI as compared t.o E1 mass spectrometry. The CI mass spectrum was obtained using a quadrupole mass spectrometer which has a lower resolution and signal-to-noise ratio than the E1 mass spectrum which was obtained using a defocused AEI MS-902 mass spectrometer. Figure 3 shows the CI mass spectrum of the species
ANALYTICAL CHEMISTRY, VOL. 46, NO. 1. J A N U A R Y 1974 * 163
.....
... . , ,
. ., -.~,
By contrast, Figure 4 shows the E1 mass spectrum of Yh(thd)s. The spectrum displays a large nnmher of fragment peaks. Similarly for reasons previously described these spectra show only that the CI mass spectrum is free from fragment peaks a s compared to the E1 mass spectrum. Figure 5 shows the CI mass spectrum of a mixture of Er(thd)j, Tm(thd)a, Yh(thd)a, and Lu(thd)j. As can he seen by looking a t the last four columns of Tahle I, a spectrum due to a mixture of these four elements could he analyzed readily since the 716 and 717 peaks are indicative of Er, the 719 peak is largely indicative of Tm, the 722, 723, and 724 peaks are indicative of Yh, and 725 peak is largely indicative of Lu. This spectrum could he used only for qualitative or semiqnantitative analysis but with computer time averaging, this method could he readily used for quantitative analysis as there are no fragment peaks. If the same mixture were run on an E1 mass spectrometer, fragmentation of the [Lu(thd)a]+ hy loss of CH3 would cause overlap with the parent peak of erbium, thus making E
Figure 4. Electron impact mass spectrum of Yb(thd)s
Figure 5. lsobutane chemical ionization mass spectrum of Er(thd)l. Tm(thd)S. Yb(thd)s, and Lu(thd)S in a mixture
Yh(thd)j. Ytterbium has seven naturally abundant isotopes: YhI6' = 0.13570, Yh"0 = 3.0370, Yhl7' = 14.3170, Yb172 = 21.82%, Yb173 = 16.13%, Yb1T4 = 31.86%, YhlTe = 12.73%. Tahle I shows that one expects to find six larger peaks, and Figure 3 shows this to he the case. There are no fragment peaks okserved in the data.
search Laboratories, Wright-Patterson Air Force Base, Ohio, who supplied the chelates used in this study. Also, we thank David Rosenthal for the use of the AEI MS-902 facilities of the Center for Mass Suectrometrv. .. Research Triangle Institute, Durham, N.C. Received for review Auril9.1973. Accented Julv 23. 1973
Preparation of Sulfur Dioxide f'or kass 3pec;iru11ieier Analyses by Combustion of SIJlfides with Copper Oxide Peter Fritz, R. J. Drimmie, and V. K. Nowicki Department at Earth Sciences, University of Waterloo, Ontario, Canada
The mass-spectrometric determination of 34S/32S ratios in natural materials is most commonly done with sulfur dioxide. The standard technique for the preparation of sulfur dioxide from sulfides or native sulfur consists of their combustion in a stream of oxygen a t temperatures between 900 and 1350 "C (1-3). This technique allows the almost total recovery of the sulfur in the form of sulfur dioxide and, therefore, has been accepted by most lahoratories. However, this conversion is not carried out under vacuum, and contamination of the sulfur dioxide by atmospheric gases of impure oxygen is possible. To overcome this disadvantage and to have another independent method, a technique for the conversion of sulfides into hexafluorides has been developed (4, 5). This technique permits the handling of extremely small samples, but its disadvantage lies in the use of extremely reactive fluorinating agents. (1) H G Thode, J. Macnarnara. and C. B Collins, Can. J. Res., 27, 361
,,"_",.
ilCll0,
(2)T. A Rafler, N. 2. J. Sci. Tech.. Sect. B , 38,849 (1957a). (3) T. A. Rafter. N. 2.J. Sci. Tech., Sect. B , 38, 969 (1957b) 14) J. R. Hulstanand H . G. Thode. J. Geoohvs. Res.. 70. 3475 11965) , ~~~. (5) H. Pucheit, B. R. Sabels, &T. C. hiering. Geochim. Cosmochim. Acta, 35, 625 (1971).
164
A N A L Y T I C A L C H E M I S T R Y . VOL. 46, NO. 1, JANUAR'I
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It is mererore aesiraDie to nave a simple preparation technique in which the preparation line can he evacuated hut which does not involve dangerous chemicals or complicated procedures. This is possible if an oxygen donor is intimately mixed with the sulfides and the combustion is carried out a t elevated temperatures. Several laboratories have begun to experiment with such a preparation technique using reagent grade cupric oxide (CuO) or cuprous oxide (CnzO) a s oxygen donors. Our findings using this technique are described.
EX1 Details of the preparation line used for these experiments ai'e shown in Figure 1. The essential parts are a combustion chamhiII and a vacuum line for the purification and collection of the sulfilr dioxide. " .^ ^ ^^^ .. . .. .*.. m e cnarge ot NU-mu mg or inrimareiy mixen oxme ana sumde is packed between quartz wool plugs in an open-ended quartz tube. It is pushed into the combustion chamber nnee the system is evacuated, and the furnace is heated to the desired temperature. The evolving SO2 is trapped with liquid nitrogen in the first cooling trap. The combustion i s complete after about 3 minutes and any excess oxygen can be pumped off. The SO3 is then distilled into the second trap hy replacing the liquid nitrogen with a cooling mixture held at about -40 "C.A total yield measurement
_. .
1974
1
.
';,,
