THE USE OF MASS SPECTROMETRY I N ORGANIC ANALYSIS
'
ERNEST I. ELIEL, THOMAS J. PROSSER, and GEORGE W. YOUNG University of Notre Dame, Notre Dame, Indiana
T H E mass spectrometer is an instrument which sorts out ions of the same mass-to-charge ratio from an ion beam containing many different ionic species and measures the relative abundance of these particles. Mass spectrometry mas first employed in work on isotopic abundance; however, more recently it has found wide application in the field of quantitative organic analysis. Since the principles of mass spectrometry are dealt with in practically all textbooks of physical chemistry (I), they will be summarized here only briefly. The material whose mass spectrum is to be recorded is admitted into the ionization chamber of the mass spectrometer a t very low pressure (ca. 10-7 mm.). This is usually accomplished by maintaining the material in a reservoir in the "inlet system" of the instrument as a gas or vapor a t a pressure of about lo-? mm. and allowing it to flow into the ionization chamber through a very small orifice called a "leak." The gas pressure in the ionization chamber is kept low hy means of continuous evacuation with a mercury diffusion pump. In the ionization chamber, the gas is bombarded by an electron beam accelerated by a potential of 50-100 volts. This produces positively charged particles (cations) as well as negatively charged particles (anions) and neutral fragments (atoms or radicals). Of these only the positive ions are accelerated into the mass spectrometer chamber proper (through an entrance slit) by means of an electric field of several thousand volts. I n the chamber, the beam comes under the influence of a magnetic field which bends i t into a circular path. The radius of
the path depends on the ratio of the mass of the cations to their charge (mle); for a given accelerating voltage V and magnetic field H this radius is R = (2mV/eH2)"'. The dimensions of the mass spectrometer chamher are such that only particles describing a certain radius R will pass through the esit slit and be recorded by the ion collector beyond it. These particles will produce a current of about 10-15t0 amps. (depending on their abundance) which is amplified and fed to a recording galvanometer which thus registers the abundance of the ions. The m/e value of the ions collected, according to the above equation, will t e R2H2/2V, i.e., it depends on the instrumental dimensions (fixed) as well as the applied electric and magnetic field. By continuously changing either the magnetic field H or the accelerating voltage V in the rourse of a spectral recording, ions of different (and known) m/e value are focussed on the exit slit in turn, and thus the mass spectrum is scanned. The result, as recorded by the instrument, is a plot of ion abundance versus m/e, exemplified by the mass spectrum of methane shown (partly) in Figure 1. When m is in units of atomic mass and e in units of electronic charge, mle is called the "mass number." If the ion hears unit positive charge, the mass number will be equal to the atomic mass of the atom or molecular fragment produced in the ionization chamber. It should he noted that mass spectra, unlike most other spectra, have to be discontinuous. since atomic masses (disregarding the small packing fractions) vary in integral units.
When a molecule, such as that of methane, enters the ionization chamber and is hit by the electron beam, i t may either be ionized as a whole or ionized and fragmented. Fragmentation almost invariablv occurs, a t least to some extent, a t the normal energy of the electron beam of 50-100 volts, but can be suppressed a t low electron energies (of the order of 10 volts). Analysis a t such low energies has been utilized in the determination of the purity of deuterated hydrocarbons (S).' The minimum potential of the electron beam a t which a particle appears is called the "appearance potential" of that fragment. As will be seen presently, it is the fragmentation process which makes mass spectrometry most useful in organic analysis. Simple ionization of methane produces the CH,+ cation with m/e = 1G. This is the most abundant ion Low ionization voltages have also been used in the analysis of CO-CO1 mixtures where the production of CO+ ions from COXis undesirable: TAYLOR, D. D., U. S. Patent 2,373,151 (1945).
JOURNAL OF CHEMICAL EDUCATION
in the methane spectrum (Figure 1). However, subsequent fragmentation with the splitting off of hydrogen also occurs, thus ions of mass number 15 (CH,+), 14 (CH2+),13 (CH+) and 12 (C+) are also observed in the mass spectrum of methane, though in decreasing .abundance. The peak a t mass number 17 is caused largely by the isotopic species CISHa+. Since the natural abundance of CI3 is about I%, and since, a prioe, the number of CLaHa+ particles from C13H4 is about the same as that of CL2Ha+particles from CL2H6 (see, however, below), the 17 peak should be about ly0 of the 16 peak, and this is borne out experimentally. The small correction for CL2H8Dis negligible in this case, because of the small natural abundance of deuterium. Formulas are available (3) for calculating the expected intensity of the so-called "satellite peaks" which are due to the natural occurrence of the heavy isotopes of carbon, hydrogen, oxygen, nitrogen, etc. Since mass spectra are discontinuous, it is unnecessary and ncedlessly expensive to reproduce them as plots of the type shonn in Figure 1. Instead, they are recorded in tabular form, as shown in Table 1. The first column in this table gives the mass number mle. The second column gives the peak height as read from the recorded spectrum. The third column gives t,he so-called "pattern," which is the peak height divided by the peak height of the highest peak and multiplied by 100. Unlike the peak height the pattern is nearly independent of the pressure of the compound in the inlet system of the instrument. TABLE 1 Meas Spectrum of Methane m/e
Peak height
Pattern
1.
...
rrr X.. 4. -.~. -
...
2"
ca. 0.Zm
The third and fifth columns of Table 2 show more complicated patterns, namely those of isobutyl alcohol and tert-butyl alcohol. I t should be noted that the "parent peak" due to the molecule-ion CIHloO+ (mle = 74) is by no means the largest peak in the mass spectrum; in fact, tert-butyl alcohol does not show any peak due to the molecule ionized as a whole, but all peaks involve fragmentation. The largest peak, or so-called "base peak" in the isobutyl alcohol spectrum is the 43 peak presumably due to (CH&CH+; the 31 peak (probably due to CH,OH+) is also quite high. In the terl-butyl alcohol spectrunl the highest peak is at + 59, due presumably to (cH~)~c-oH. It should be noted t,hat all of these high peaks correspond to carbonium ions which are stabilized by resonance or hyperconjugation, and it is usually true dhat peaks due to such ions are large. The reverse is not true, however; thus int,ense peaks (such as the 33 peak in the isobutyl alcohol spectrum) may not correspond to any obvious stabilized carbonium ion. A case in point is found in the spectrum of m-xylene vhere the base peak is a t m/e 91. According to the intuition of the organic chemist, the CH,C6H4+ion 1%-ouldnot be expected to be particularly stable.* There are two types of peaks which cannot be readily explained by fragmentation. In some cases, rearrangements occur in the process of ionization; thus 2,s-dimethylhexane, (CH,),CHCH,CH,CH(CH& shows "rearrangement peaks" at m/e 29 and 85, due, respectively, to C2Ha+and C6H13+;these ions cannot be formed from the parent- molecule by a process of simple bond rupture and ionization. Occasionally, such rearrangement peaks are of major importance; thus in the spectrum of 3-ethyl-3-phenylpentane, C6HIC(C1H& the base peak corresponds to m/e=9l. This peak cannot be formed from the molecule by simple fragmentation, but probably is due to C6HsCH2+ formed by ionization followed by rearrangements (28). Some peaks are due t,o "metastable ions," i.e., 'This particular anomaly has recently found an ingenious P. X., S. MEYERBOS, A N D H. hI. explanation; ef. RTLANDER, GRZTBB, Division of Petroleum Chemisty, A.C.S., Preprints, Val. 1, No. 3, 111 (1956).
Not shorn in Figure 1; values taken from the literature.
TABLE 2 Mass Spectra of Isobutyl and Tert-Butyl Alcohol and Mixtures Thereof
(CH&CHCH20H mle
15 27 29 31 33 41 12 43
59 74
Peak height 24.0 380.0 218.4 580.0 368.0 481.0 440.0 741.0 52.1 68.8
Pattm 3.24 51.28 29.47 78.27 49.66 64.91 59.38 100. no 7.03 9.28
Pressure, p 15.41 Sensitivity: 48.09 ( = Height of base peak divided by Pressure)
YOLUME 34, NO. 2, FEBRUARY, 1957
(CHdaCOH Peak height 222.0 123.3 170.0 454.0 1.8 297.0 54.1 227.0 1314.0 0.0
-
Pattern 16.89 9.38 12.94 34.55 0.14 22.60 4.12 17.28 100.011 0.00 14.00 93.86
Wirture spectra (peak heights)
--
1st ...
Znd
3rd
...
...
...
... ...
54610 192.0 ...
s.ii:o 194.
547:0 192.9
506:0 723.0 35.0
5i5:o 135.0 35.9
5ii:o 728.0 35.9
15.2
15.6
15.09
...
...
...
...
...
73
ions which break down further after leaving the ionizing chamber; these ions do not conform to the equation for m/e given above since the particle accelerated in the electric field V has a different mass from the particle bent in the magnetic field H after breakdown
(4.
Molecules labeled with heavy isotopes, such as D, C13, N16, etc., Nil1 give mawspectral patterns considerably different from those of their light analogs. This is due not only to the increased mass of the molecule as a whole or of those fragments containing the heavy isotope, but also to a slight extent to the fact that strengths of the bonds involving such isotopes are higher than those involving light isotopes. This will decrease the probability that certain fragments will be produced and thus decrease the intensity of the peaks due to these fragments. Thus, the intensity of the 18 peak (due to CD,+) in tetradeuteromethane is 83.0% of that of the 20 peak (CD4+) while the intensity of the 15 peak (CHa+) in a methane spectrum obtained by the same investigators (6)is 86.1% of that of the 16 peak (CH4+). This indicates more extensive fragmentation of the hydrogen compound. Similar results have been obtained in chloroform spectra (6) where more extensive formation of the CCla+ ion occurs with CHClr than with CDCL. QUANTITATIVE .ANALYSIS
Although mass spectrometry may be of use in qualitative analysis (7), its principal use is the quantitative analysis of mixtures of known components. This development was pioneered by the petroleum industry, but its usefulness is more far-reaching than many organic chemists realize. Mixtures of up to about a dozen components may be analyzed rapidly and with high accuracy (*l%). Speed and accuracy are the main advantages of the mass spectrometric method over other instrumental methods, such as infrared analysis. Disadvantages are the cost of analytical mass spectrometers (of the order of $45,000) and their somewhat greater intricacy as compared to other instruments. The closest competitor to mass spectrometry as an analytical tool is probably vapor phase chromatography (S), which is considerably cheaper and simpler, but also considerably less versatile. A combination of the two techniques is possible where the eluate gas from a vapor phase chromatogram is introduced in a mass spectrometer (9). Quantitative analysis using mass spectrometry is based on the assumption (usually valid) that the spectrum of a mixture is a sum total of the spectra of all the components in the mixture. The one necessary condition for carrying out an analysis is that each component posseses a unique spectrum. (See under "Limitations" regarding the validity of this assumption.) Calculations are based on the equation H, = S,P, where H. = peak height (scale divisions), P = pressure (,u) and S. (div./,u) is a proportionality constant called "sensitivity." Sensitivity is calculated from the spectrum of a pure compound for any desired peak by simply dividing the peak height (H.) by the total pressure (P) of the sample. Thus, the sensitivity value corresponds to the contribution of the given compound to the given peak for unit pressure of that
compound. Sensitivity varies with instrumental response and thus is not a universal constant. Sensitivity values must be obtained from spectra recorded on the same instrument as the unknown mixture and under the same instrumental conditions. The constancy of instrumental conditions is checked by daily calibration runs on known compounds, such as n-butane, in which the sensitivity of the major peak of the calibration substance (43 for n-butane) should remain constant. I n practice, for analysis of a mixture containing components A, B, C,.....N, n peaks are picked from the spectrum of the mixture. These peaks, ideally, are chosen such that each peak is exclusive or nearly so for one component. Such a stringent condition cannot usually be fulfilled and all of the peaks chosen will probably have some small contribution from each of the other components. We may then write the following set of simultaneous equations:
Here HI, HI, etc., stand for the peak heights a t the mass numbers chosen. PA,PB,etc., correspond to the partial pressures of components A, B, etc. SIAcorresponds to the sensitivity of component A a t the mass number of HI with similar meanings for SIB, SIC,etc. The H, and 8, values are determined experimentally and thus the P values may be found by solving the above system of simultaneous equations. vhere
Then %A = 100PA/PT;%B = 100PB/PT;etc PT = PA + P B + Po + . . . . . + P N
In some cases it is found that a mixture peak can be attributed exclusively to one component. Such is the case if this component has a greater molecular weight than any other substance in the mixture and its parent peak is appreciable. The partial pressure of this compound can be calculated directly from its parent peak using H, = S,P. The entire contribution to the spectrnm due to the known compound can then be obtained by using its calculated pressure and the appropriate sensitivity values. This contribution is subtracted from the mixture spectrum. The procedure is repeated as many times as possible whereupon the remaining components are analyzed by solving simultaneous equations as above. With four or more simultaneous equations, a computer is usually resorted to. Electrical computers specially designed for solving systems of up to twelve linear simultaneous equations with up to twelve unknowns as encountered in mass spectrometry are available. For routine operations, faster (but more expensive) electronic computers are often used. A convenient check on the accuracy of a calculation is a comparison of PT(calculated) to the experimentally observed total pressure. If these two do not coincide one might suspect the presence of an unaccounted-for component. If such is the case, new peaks, not used in the original calculation, are chosen from the mixture spectrum, and the sensitivity values are calculated a t these peaks for each component from its authentic spectrnm. The expected height of any peak in a mixture can then be calculated as follows: JOURNAL OF CHEMICAL EDUCATION
Here, the S. and P values are known and the H. value is calculated. If the calculated and observed values do not coincide to within 1%, then one has what is termed a residue or residual peak (R,) defined as R. = H , (observed) - H , (calculated). Often by examining the residues a t various mass numbers, one may be able to identify the unaccounted-for component, assuming that its mass spectrum is known. An example from the authors'laboratory will illustrate the method. I t is concerned with the analysis of a synthetic misture of isobutyl and tert-butyl alcohol containing 51.70% of the former and 48.30% of the latter. The mass spectrometric data required for the analysis are recorded in Table 2. The 33 and 59 peaks were selected for calculation since a t m/e=33 the contribution of isobutyl alcohol is large aud that of tert-butyl alcohol is small, and the reverse is true a t 59. From columns 2 and 4 in Table 2 the sensitivities are: Saat = 23.88, Saat = 0.13, S a g t = 3.38 and &' = 93.86 where the superscripts i and t refer to isobutyl and tert-butyl alcohol, respectively. Then, setting up equations (1): 23.88 P s + 0.13 PL= 192 3.38 P'
+ 93.86 P'
=
723
where P' = partial pressure of isohutyl alcohol and P' = psstial pressure of tert-butyl alcohol
The solution is P' = 8.00 p, P' = 7.41 p ; total pressure PT,calculated 15.41 p, actual 15.09 p. % isobutyl alcohol (from equation (2)) 51.91%, % tertbutyl alcohol 48.09%. The second and third analysis gave % isobutyl 51.82, 51.87; % tertbutyl 48.18, 48.13. The agreement of the three analyses with each other and with the actual composition of the sample (% isobutyl 51.70; yo tert-butyl 48.30) is excellent, probably somewhat better than average. Residuals were calculated at 31, 43, and 74 using the sensitivities a t these peaks to calculate the expected peak heights by equation (3) and subtracting the actual peak heights from these; the results are given in Table 3. All residuals are less than ly0 of t,he peak TABLE 3 Calculation of Residuals
- -- -Smitivitya
Peak height
Re3idualsd
cnlc~r-
m/e
iso
tert
found'
laledc
A
B
C
Peak height divided by pressure from spectra of pure components in Table 2; iso refers to isobutyl alcohol, tert to lwtbutyl alcohol. First wectrum. Table 2. a Using equation (3). Found peak height minus calculated peak height. A is for the 1st ~pectrum,Table 2, calculated in this table. Band C refer to the 2nd and 3rd snectra in Table 2: calculation not shown.
(or less than one scale division for peaks under peak height 100) which is considered a satisfactory check on the accuracy of the analysis and indicates the absence of unacconnted-for components. It should be stressed that the mixture illustrated in this example was a synthetic one made up of pure compounds; VOLUME 34, NO. 2, FEBRUARY, 1957
actual mixtures encountered in organic work will rarely give such clean-cut results because of the likely presence of minor contaminants. Alternative methods for carrying out these calculations cannot he illustrated here because of space considerations but are detailed in texts on mass spectrometry (10). TRACER STUDIES
Mass spectrometry is used in tracer studies involving nonradioactive nuclides in one of two ways. In the more common, though less powerful technique, mass spectrometry is used to analyze for the amount of the tracer present in a given sample. This amount is usually expressed as a percentage of the total amount of the element in question, and the analysis is sometimes called a determination of the isotopic ratio. The technique involved is to convert the element in question into a low-molecular-weight gas, and to determine mass spectrometrically the ratio of heavy to light isotope in this gas. For example, to determine C13 as percentage of total carbon in a sample, the sample is burned to carbon dioxide in the usual analytical combustion train, but the carbon dioxide is collected in a liquid nitrogen trap instead of being absorbed chemically. It is subsequently put into the mass spectrometer, and the ratio of C13 to CLZ is found from the ratio of the 45 (Cla02) to the 44 (ClZ02)peak (11). Nitrogen is analyzed similarly as Nz (obtained from the organic sample by a Kjeldahl digestion followed by hypobromite oxidation of the ammonia) on the basis of the height .of the 30 (WN16), 29 (N15?74) and 28 (N14NNL4) peaks (12). I n some cases, the nitrogen given off in an organic reaction, such as the Curtius reaction RCONa RNCO + Nz, has been subjected to
-
L
analysis (18). (It was shown that R-CN'4=N14= 0 NL5 upon rearrangement gives R-NL4=C=0 and N14NN".) While a mass spectrometer (not necessarily of the analytical type--a less expensive isotope ratio instrument is sufficient) is essential in the analysis of iV4 and Cia, its use in the analysis for deuterium is optional. Excellent methods for the determination of deuterium by measuring the density of the water obtained in the C0mb~~tiOn of the given organic compound are available (14). Alternatively, the water may he decomposed to elementary hydrogen (15), e.g., by means of hot zinc or uranium (16), and the hydrogen-deuterium mixture analyzed mass spectrometrically on the basis of the 4 (D*), 3 (HD) and 2 (H2 D) peaks (17). Mass-spectrometric analysis of water itself is difficult because of its strong absorption on the walls of the mass suectrometer assemblv (18). A much more powerful, though as yet less extensively used application of mass spectrometry is in the so-called isotope position technique (19). Here the labeled organic compound is introduced in the spectrometer as such. From the fragmentation pattern, the position of the tracer in the molecule can he seen directly. For purposes of quantitative analysis, it is usually necessary to synthesize pure species with the tracer in known positions, since, for the reasons stated
+
above, it is rarely possible to predict the mass spectrum of a labeled molecule from that of the unlabeled one. (See, however, (to).) The method is well illustrated xvith an example from the authors' laboratory (21). (For other examples, see 22). I n the course of an investigation, it became necessary to ascertain whether a sample of deuterated isobutyl alcohol was (CH3)zCDCHz0H or (CH& CHCHDOH or a mixture of the t1r.o. This evidently cannot be done by the isotope ratio method mentioned preriously, since both isomers contain 10 atom-per cent deuterium. I t is possible to carry out the determinat,ion by oxidation of the alcohols to the acids (CH& CDCOOH and (CH&CHCOOH and elementary deuterium analysis of the latter, (this was, in fact done (91)), but such a determination is tedious, since it must be ascertained that no exchange of the denterated acid takes place in the course of the oxidation; moreover, if one starts out with a mixture and the oxidation is not quantitative, the result may be vitiated by an isotope effect in the oxidation (21). I n the actual analysis, authentic samples of (CH,),CDCH,OH (isohutpl-2-D alcohol and (CH3)2CHCHDOH (isobutyll-D alcohol) were synthesized. (The synthesis of snch authentic samples does not usually present insuperable problems and the purity of the samples may be checked by mass spectrometry.) Mass spectra of the authentic alcohols and of the mixture to be analyzed were then recorded, and the composition of the mixture was calculated as described above under "Q.uantitative Analysis," using mass peaks a t 31, 32, and 43. The major peaks in the spectrum of isobutyl alcohol are 43 [(CH3)2CH+]and 31 (CHzOH+). I n the 1-D compound the major peaks are 43 and 32 (CHDOH+); and in the 2-D compound they are 44 [(CH&CD+] and 31. The isotope dilution met,hod (23) has also been used in conjunction with mass spectrometry. LIMITATIONS
Despite the wide applxability of mass spectrometry, the method is subject to certain limitations which shonld be understood clearly. The pressure in the inlet system of the substance or mixture whose spectrum is to be recorded must be a t least of the order of mm. A solid or liquid whose vapor pressure is less than 10 p a t room temperature cannot be handled by the ordinary inlet system. However, the range of the instrument can be greatly extended by the use of inlet systems which are heated electrically to temperatures as high as 300°4000C. (24, 25). Another limitation is imposed by the limit of resolution of the instrument. As m/e increases, the separation of two subsequent peaks of mass number n and n 1 decreases. The limit of resolution is reached when the two peaks are no longer separated. In some cases a mixture cannot be analyzed for two or more components individually because their mass spectra are too similar. Stereoisomers usually fall into this category, for example, cis- and trans-2butene. A similar difficulty is encountered with positional isomers among olefins and alkylbenzenes; thus there are no salient differences between the mass
+
spectra of l-butene and Z-butene or between m-diethylbenzene and pdiethylbenzene. Sorption on the glass n-alls of the mass spectrometcr assembly may cause difficulty in the analysis of oxygenated compounds (24, 26). Because of this, mistures of light and heavy water cannot readily be analyzed by mass spectrometry (18). However, t,he presence of small amounts of water in an organic sample is not likely to cause difficulty. The seriousness of the sorption problem depends on t,he t,ype of instrument and the type of analysis (27). Sensitivities tend t,o fluctuate and need to be redetermined from time to time for the pure standards. I n contrast, patterns are constant over periods of time in a given instrument. Unfortunately, patterns are not quantitatively reproducible from one inst,rument to another. This means t,hat comparison of patterns with those recorded in the literat,ure can be only qualitative. Small amounts of impurities, provided they have a few high mass peaks; may appreciably modify the spectra of compounds m-hich they contaminate. This fact may he of considerable nuisance value to the ordinary organic chemist ~ h iso not concerned with the presence of 2% or 3% of impurities in his samples. This situation is quite different from what it is in the infrared, where small impurities usually do not interfere. On the other hand, extraneous peaks may prove valuable in the identification of iuteresting minor components of a given mixture. CONCLUSION
In conclusion, it maybe said that mass spectrometry is a valuable analytical tool for the organic chemist who deals with compounds of molecular weight below about 600 and of appreciable volatility. The work is aided by the availability of a number of excellent summaries and reviews (4, 5, 29-35) and, subject to the limitations mentioned above, by the collection of a large number of mass spectra of common compounds (56). ACKNOWLEDGMENT
This paper is a contribution from the Radiation Project of the Tnirersity of Xotre Dame, supported in part under Atomic Energy Commission contract AT(l1-1)-38 and Kavy equipment loan contract Nonr-06900. We are grateful to Professor Russell R. Williams of this Department aud to Mr. Seymour Meyerson of the Standard Oil Company (Indiana) for helpful suggestions. LITERATURE CITED (1) See also NORTON, F. J., J. CHEM. EDUC., 25,677 (1948).
(2) STEVENSON, D. P., A N D C. D. WAGXER, J. Am. Chem. Soc., 72, 5612 (1950). (3) W a s ~ s m tH. ~ , W., "Mass spectrometry" in BERL,W. G., "Phpical Methods in Chemical Analysis," Academir Press, Inc., New York, 1950, Vol. I, pp. 615-17. D. W., "Ma88 spectrometry" in WEISSBERGER, (4) STEWART, A,, "Physical Methods of Organic Chemistry, 2nd ed., Interscience Publishers, h e . , New York, 1949, Vol. I, Part 11. n. 2015: also ref. (3). no. 601-2.
JOURNAL OF CHEMICAL EDUCATION
(7) E. g., KINNEY, I. W., AND G . L. C o o ~ , A n a IChem., . 24,1391 ( 1 9.52). (8) Chem. and Eng. News, 34, 1692-6 (1956); PODBIELNIAK, W. J., AND S. T. PRESTON,Pelwleum Refiner, 34, 165 (1955); 35,215 (1956); DIMBAT,M., P. E. PORTER,A N D F. H. STROSS, Anal. Chm., 28,290 (1956); FREDERICES, Anal. Chem. 28,297; EGGERTE. M., AND F. R. BROOKS, S E N , F. T., H. S. KNIGHT,I N D S. GROENNINGS, Anal. Chem. 28. 303. DREW,C . M., J. R. MCNESBY,S. R. SMITH,A N D A. S. Anal. C h m . 28,979 (1956). GORDON, MITCHELL,J. J. "XBSSspectroscopy in hydrocarbon analysis" in FARKAS,A., "Physical Chemistry of the Hydrocarhons," Academic Press, Inc., 1950, Val. I, p. 95. WILSON, D. W., A. 0. C . NIER, AND S. P. REIMANN, "Preparation and Measurement of Isotooic Tracers." J. W. 9 22Edwards, Ann Arbor, Michigan, 194;, pp. 4 ~ 4 and 24. Ibid.. DO.31-39 and 20-22 BOTHNEE-BY, A. A,, A N D L. FRIEDMAN, J . Am. Chenz. Soe. 73,5391 (1951). Ref. ( l l ) , pp. 51-65; KIRSHENBAWM, I., "Physical Properties and Analysis of Heavy Water," McGraw-Hill Book Co., Inc., New York, 1951, pp. 260-375. Ibtd., pp. 187-259; ref. (IS'), pp. 81-90 (by ROTH,E.). J.. M. L. PERLMAN. A N D H. C . PROSSER. Anal. . . BIGELEISEN. Chm. 24,'1356 (1952). (17) Ref. (11), pp. 24-25; ref. (Id), pp. 69-186. H. W., C. E. BERRY,AND L. G. (18) See, however, WASHBURN, HALL,Anal. C h m . 25, 130 (1953). (19) Ref. (S), pp. 618-20. (20) "Applied Mass Spectrometry," The Instituted Petroleum, London, 1954, pp. 91-93 (by BOND,G . C.). (21) ELIEL,E. L., AND TH. J. PROSSER, J . Am. Chem. Soe., 78, 4045 (1956).
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VOLUME 34, NO. 2, FEBRUARY, 1957
(22) FRIEDMAN, L., AND J. TURKEYICE, J . Am. Chem. Soe., 74, F. A,, AND L. FRIEDMAN, J. Am. 1669 (1952): LONDON, C h m . Soc., 72, 3692 (1950). (23) Ref. (41, p p 2027-30; ref. (S), pp. 621-22. (24) THOMAS, B. W., AND W. D. SEYPRIED, Anal. C h m . 21,1022 (1949). Anal. Chem. 23,830(1951); (25) O'NEAL,M. J., ANDT.P. WEER, MELPOLDER, F. W., R. A. BROWN, T. A. WASHALL, W. AND W. 8. YOUNG, A d . Chm. 26, 1904 DOHERTY, (1954); @NEAL,M. J., ref. (181, pp. 2 7 4 6 . (26) GIFFORD, A. P., S. M. ROCK,AXD D. J. COMAFORD, Anal. Chem. 21, 1026 (1949). (27) KELLEY,H. M., Anal. Chem. 23,1081 (1951). N. 01 Prrroleum (28) HYIANDER,P. S., A x n S.M E Y U H ~ UDivisi~n Checni,rry, .I. C. d., l'rt.prinrr, \'ol. I , No. 3, 105 (I!)X,). (29) Ref. (S), pp. 587-639; ref. (4), pp. 1991-2058. (30) Ref. ( l o ) , pp. 83-111. (31) BARNARD, G. P., "Modern Mass Spectrometry," The Institute of Physics, London, 1953. (32) ROBERTSON, A. J. B., "Mess Spectrometry," John Wiley & Sons, Inc., New York, 1954. (33) DUNNING, W. J., Quart. Reu., 9, 23 (1955). (34) HIPPLE, J. A,, AND M. SHEPHEED, Anal. C h m . 21, 32 M., AND J. A. HIPPLE,Anal. Chem. (1949); SHEPEERD, 22, 23 (1950); DIBELER,V. H., AND J. A. HIPPLE,Anal. Chem. 24,27 (1952); DIBELER,V. H., Anal. Chem. 26,58 F. W.. Anal. Chm. 28.306 f 1956).(1954): MCLAFFERTY. (35) DDENBOSTEL, B. F., AND W. PxmTmT, Chem. and Eng. News, 32, 4736 (1954). (36) American Petroleum Institute Research Project 44, "Mas8 Spectrd Data," Carnegie Institute of Technology, Pittsburgh. Pa.
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