V O L U M E 2 4 , NO. 1, J A N U A R Y 1 9 5 2 Murakawa, K , and Ross, J . S.,Ibid., 82, 967 (1951). Ibid., 83, 1272-3 (1951). Murakawa, K., and Suwa, S., Ibid., 76, 433 (1949). Nachtrieb, N., “Principles and Practice of Spectrochemical Analysis,” New York, MoGraw-Hill Book Co., 1950. Nagata, M., J . Chem. Soc. Japan, 70, 410-11 (1949). Pearse, R. B., J . Optical Soc. Am., 41, 148-52 (1951). Pfeilsticker, K., Spectrochim. Acta, 4, 100-15 (1950). Poehlman, W. J., and Sarnowski R E., J . Optical SOC.Am., 41, 869 (1951). Ranade, J. D., Phil Mag., 42, 279-83 (1951). Rouse, A. G., J . OpticaE SOC.Am., 40, 82-4 (1950). Russell, H. Ii., Ibid., 40, 550-75 (1950). Ibid., pp. 618-19. Sawyer, R. A., “Experimental Spectroscopy,” 2nd ed., New York, Prentice-Hall, 1951. Schmidt, T., 2. Phyrik, 108, 408-20 (1949). Schroder, G., Klin. Wochschr., 28, 759 (1950). Scribner, B. F., and Meggers, W. F., “An Index to the Literature of Spectrochemical Analysis, Part 111” (in preparation). Seith, W., and Ruthardt, K., “Chemische Spektralanalyse,” Berlin, Julius Springer, 1949. Shaw, D. M., Joensun, 0. I., and Ahrens, L. H., Spectrochim. Acta, 4,233-6 (1950). Shenstone, A. G., and Wileta, L , Phys. Rev., 83, 104-8 (1951). Smith, D. D., and McNally, J . R., Jr., J . Optical Soc. Am., 40, 878 (1950).
27 Smith, D. D., Stukenbroeker, G. L., and JIcSally, J. R., Jr., Phys. Rev.,84, 383 (1951). Smith, D. XI., Met. itul., 43, 121-8 (1951). Smith. R. G., Craig, P., Bird, E. J., Boyle, A. J., Iseri, L. T., Jacobson, S. D., and Myers, G. B., Am. J . Clin. Palh., 20, 263-72 (1950). Strasheim. A.. Svectrochim. Acta. 4. 2-7 (1950). Ibid., pp. 200-1;. Strasheim, A,, Union S. Africa Dept. Agr. Sci., Bull. No. 295, 12 PP. (1949). Stukenbroeker, G. L., and McNally J. R., Jr.. J . Optical SOC. Am., 40,336 (1950). Stukenbroeker, G. L., Smith, D. D., Werner, G. K., and hIcNally, J. R.. Jr.. Ibid., 41, 869 (1951). Suwa, S.,Phys. Rev., 83, 1258-9 (1951). Suwa, S., Rept. Inst. Sci. and Technol. Univ. Tokyo, 3, 269-75 (1949). Swings, P., J . Optical SOC.Am., 41, 153-65 (1951). Theirs, R. E.. Ibid., 40, 849-51 (1950). Tomkins, F. S.,Fred, hl., and Meggers, W.F., Phys. Rev., 84, 168 (1951). Traynard. P., Rev. mht., 47, 409-20 (1950). Wijnen, J., and Tiggelen, A. van, Spectrochim. Acta, 4, 8-12 (1950). Yanagata, K.,J . Chem. SOC.Japan, 71, 288-92 (1950). Young, J. F., Iron Age, 168, 91-2 (1951). RECEIVED Xorember 14, 1951.
MASS SPECTROMETRY VERNON H. DIBELER
AND JOHX
A. HIPPLE
National Bureau of Standards, Washington 25, D . C .
T
WO previous reviews of the literature on mas8 spectrometry have appeared in this journal. In the interval, since the last review (177) the large number of publications indicates a continuing increase in the use of the mass spectrometer in fundamental and applied research. Improvements in instruments and techniques have contributed to an increase in the speed and accuracy of analysis for the chemist and have also extended the field of application. An increasing number of laboratories are exploiting the mass spectrometric techniques for the study of dissociation processes and of reaction kinetics. ils in the past, the work in physics promises the development of new methods of ion analysis which will h d future application in chemistry. In addition to this, the overlapping interests of chemists and of physicists in mass spectrometry make it desirable that this survey be as complete as possible for both groups. INSTRUM ENTS ,METHODS, AND TECHNIQUES
Descriptions of analytical instruments of the magnetic deflection type which incorporate various modifications, improvements, and special features have appeared in the literature (5,10,15, 20, 61, 111, 118, 185, 196, 207, 209, 210). T h e groupworkingwith Urey has described the experimental arrangement whereby it has been able to attain high precision in making relative measure ments of isotopic abundance (123). Two new instruments for doublet measurements have been described: that of Duckworth (50) and that of Nier and Roberts (140) in which high &ability is attained by means of an auxiliary ion beam. Four papers deal with source problems ( 7 , 16, 26, 153). A continuing interest in radio-frequency and time-of-flight mass spectrometers which involve no magnetic field is apparent (2%, 23, 84,108, 174). A similar interest has continued in the timing instruments that are based on the principle of cyclotron resonance (18,91,98, 179,180,183,184). Leak detectors of various designs are detailed (161, 193, 217). T h e problems in sample systems of avoiding stopcock grease and of handling liquid samples have been solved in several ways
(45, 73, 87, 156, 160, 220). Other special topics are covered: mass indicator ( S I ) , electron current regulator ( S Z ) , leaks for controlling flow (66, 80), precision slit (65),and metal gasket (89) Geerk and Brix have studied the blackening of photographic plates by protons through the use of a mass spectrograph of the Thomson type (75). ION OPTICS
The references listed in this section are concerned primarily with theoretical studies aimed a t improvement of the focusing properties in ion sources (34, 150, 215) and analyzers (53, 36, 86, 88, 99, 133, 150, 169, 194, 212). Most of them treat variations of the instruments employing sectored magnetic fields because of the greater design flexibility permitted by tilting or shaping the boundaries of the magnetic field through which the ions pass. T h e aim of these efforts has been to achieve wider angle focusing (second or higher order) or two-directional focusing. Ploch and Walcher (154) have studied the effect of the stray field and the latter has reviewed the ion optics involved in mass spectrometry (214, 216). Sakai has suggested an arrangement which is presented as a perfect velocity-focusing mass spectrometer (170). Svartholm (195) describes a combination of crossed, nonuniform electric and magnetic fields by which it is expected to achieve both two-directional and velocity focusing of ions. IONIZATION AND DISSOCIATION BY ELECTRON IMPACT
Much effort has been devoted t o obtaining mass spectral data of a wide variety of compounds including isotopically substituted molecules, organometallics, isomeric hydrocarbons, and compounds of high molecular weight. Condon ( 4 1 ) and Condon, McMurry, and Thornton (42) have reported the mass spectra of some hexa-, hepta-, and octadeuterated derivatives of propane. Dibeler and Bernstein (44)have measured the isotope effect on dissociation probabilities in the mass spectra of chloroform and
28 chloroform-d. Schaeffer (171) has described a general method for calculating the effect of isotopic substitution on mass spectra of molecules. All of the deuteromethanes were synthesized and the mass spectra obtained by Dibeler and Mohler (46). Mass spectra of N';, N14N16,and N1g were reported (47), as well as the dissociation probabilities of HP, Dz, Tz (48, 173) and H D , H T , C1*O, C t S O (48). ~ The spectra of diborane-dg and of ethanedg were measured (49) and compared with the spectra of the normal molecules. Norton (142) compared the spectrum of B1: Hg with the calculated spectrum of normal diborane. Stevenson and Wagner (191) obtained the spectra of Ct to C, monodeutero paraffins and compared these with the corresponding spectra of the normal hydrocarbons. Baldock and Sites ( 6 ) studied the dissociation of some nickel carbonyls. Brannon, Dozier, and Carr (65) reported studies of a series of organic phosphorus compounds. Mohler and coworkers have reported studies of a series of isomeric hydrocarbons including CBHBisomers (126), cis- and transdecahydronaphthalene (128), and the isomeric nonanes (129). The total ionization of hydrocarbons was studied by Mohler, Williamson, and Dean (127). O'Neal and Wier (147) modified a standard Consolidated mass spectrometer to permit the introduction of completely vaporized samples of hydrocarbons up t o C40and t o provide a mass range up to approximately M / e = 600. Ewald and Henglcin ( 6 8 ) observed ion dissociation with the aid of a parabola spectrograph. Sites and Baldock (178) reported ionization and dissociation studies. Langer (117) discussed rearrangement peaks observed in some mass spectra of hydrocarbons and oxygen-containing compounds. The effect of temperature on the mass spectra of a number of hydrocarbons was studied by Berry (13) and by Reese, Dibeler, and Mohler (159). Berry (14) reported on the effects of initial energies on mass spectra and discrimination effects in the mass spectrometer. Studies of negative oxygen ions were reported by Watanabe and Mida (219). Dukel'skil, Zandberg, and Ionov determined the negative ion spectra of the chlorides of rubidium and cesium (60) and of the chlorides and iodides of lithium, sodium, and potassium (59). Bates, Fundaminsky, Leech, and Massey ( 8 , 9 ) have published mathematical papers on the excitation and ionization of atoms by electron impact, discussing in particular the Born and Oppenheimer approximations. Mitchell and Coleman (125) discussed the effect of impact parameter, distribution of electron energy, and transition energy on appearance potentials of hydrocarbons. Warren (218) described a graphical method of extrapolated differences to evaluate appearance potentials. Fox, Hickam, Kjeldaas, and Grove ( 7 1 ) have reported an important advance in the technique of measuring appearance potentials. By using a pulsed electron beam and appropriate stopping potentials to obtain a nearly monoenergic electron beam, they have succeeded in making direct measurements of ionization probabilities and appearance potentials. Tickner, Bryce, and Lossing (201) reported measurable differences in the appearance potentials of the deuteromethanes, the difference increasing with the extent of deuteration. Burhop, Massey, and Watt (28) studied the ionization and dissociation of uranium tetrachloride and hexafluoride. -4ppearance potentials of some metastable transition ions found in hydrocarbon mass spectra were measured by Fox and Langer ( 7 2 ) . Geerk and Neuert (76) reported the ionization and dissociation of methane, methanol, and methylal. Appearance potentials of the several ions in germanium hydride were measured by NBve de MBvergnies and Delfosse (137). Osberghaus (149) reported the appearance potentials of electron impact products of boron trichloride and trifluoride. Values of the ratio Blo/Bl1were also given for a
ANALYTICAL CHEMISTRY number of sources of boron. Ionization and dissociation of cyanogen, hydrogen cyanide, and cyanogen chloride were studied by Stevenson (188). Kambara measured appearance potentials of hexane, cyclohexane, and benzene (101), n-propyl alcohol (102), isopropyl alcohol (103), and acetone and acetic acid (104). Field (69) reported a new calculation of the latent heat of sublimation of carbon and the first C-H dissociation energy in methylene. Field and Hinkle ( 7 0 )measured the ionization potential of cyclopropane. APPLICATION TO PHYSICAL CHEMISTRY AYD CHEMICAL KINETICS
The kinetics of the pyrolysis of diborane was studied by Bragq, McCarty, and Norton (24). Coggeshall and Kerr (58) repoited mass spectrometric studies of thermal decomposition products of various hydrocarbons. Coggeshall ( 3 7 ) described the role of mass spectroscopy in the determination of organic functionality. Wall and Moore (216) studied the pyrolysis of 50-50 mixtures of ethane and ethane-&. Norton (1.48) presented evidence for the existence of a new boron hydride, possibly BaH13, in diborane stored for a long time a t -78" C. The important application of the detection of intermediate reaction products by mass spectroscopy was discussed by Eltenton (62). The method x a e based on the fact that in general the ionization potential of radicals is lower than the appearance potential of the same ion produced from a parent by electron impact, thus permitting the separate detection of radicals. Several papers reported mass spectrometric studies of various nickel-catalyzed reactions. Kemball (120) studied the reaction of methane and deuterium on evaporated nickel catalysts. Taylor and Dibeler (191) reviewed recent mechanisms proposed for the catalyzed reactions of unsaturated hydrocarbons with protium and deuterium and presented some new experimental results. Wright and Taylor (221) reported on the interaction of methane and methane-& on nickel and on the state of the nickel catalyst. Turkevich, Bonner, Schissler, and Irsa (206) discussed the use of stable and unstable isotopes and the application of the mass spectrometer to catalytic research. Fractionation of the carbon isotopes in decarboxylation reactions was studied by means of the mass spectrometer. Bigeleisen and Allen ( 1 7 ) reported on the relative rates of decomposition of 1-C'* and l-CI3 trichloroacetate ions. Bothner-By and Bigeleisen (21) studied the relative rates of decomposition of carboxyI-C'z and -C13 mesitoic acids. Lindsay, Bourns, and Thode (120) reported on the carbon 13 isotope effect in the decarboxylation of nmalonic acid. Lindsay, JlcElcheran, and Thode (121) studied a similar reaction of oxalic acid. Landeen, Farnsworth, and Sherburne (116) described the application of a mass spectrometer to the study of surface reactions at low pressures. Plumlee and Smith (155) reported a preliminary study of sublimation characteristics of oxide cathode materials and Stier (192) studied the activation of barium oxide cathodes. Tickner and Lossing (209,203)have applied the mass spectrometer to the measurement of vapor pressures of a number of light hydrocarbons and carbon dioxide in the range of 0.001 to 10 mm. ANALYTICAL APPLICATIONS
Rock (166) has stressed the value of mass spectrometric analysis in the qualitative resolution of mixtures. Spectra of 279 compounds were tabulated and classified. Various means of identifying compounds in mixtures were discussed. These included the use of isotope abundance ratios, the presence of ions resulting from metastable transitions, etc. Burkhard and Norton (29) applied the mass spectrometer to the qualitative analysis of organosilicon compounds and polymers. Univalent hydrocarbon radicals directly attached to silicon were connected to the related hy-
V O L U M E 24, NO. 1, J A N U A R Y 1 9 5 2 drocarbon gas by heating with concentrated sulfuric acid and admitted directly to the mass spectrometer. Qualitative analysis aided by a punched-card catalog of mass spectral data was described by Zemany (2%). Several papers reported methods of detecting trace amounts of impurities, particularly in samples of hydrocarbons highly enriched in C13 and in deuterium. Methods described by Honig (92), Stevenson (189), and Stevenson and Wagner (190) were based on the properties of the initial portions of the ionization efficiency curves of the molecule ions and of the fragment ions. Rollmann and McMurry (168) used parent-peak intensities as a basis for estimating purities of deuterium substituted compounds. Happ, Stewart, and Brockmyre (81) reported procedures for determining most of the ordinary contaminants in air (except carbon monoxide) in quantities below 100 p.p.m. Quantitative microanalyses of mixtures of nitrogen, oxygen, and hydrogen were described by Kambara (100). Two methods of analysis of particular interest to petroleum laboratories were reported. Broa n (27) described the analysis of gasolines in which compound t-ypes were determined. The procedure was considered extendable to type analysis of higher boiling fractions and to nonhydrocarbons. O’Neal (146) described the use of mass spectrometric and infrared data for the analysis of certain hydrocarbon mixtures. Gorman, Jones, and Hipple ( 7 7 ) described the isotopic and chemical analysis of solids by means of a mass spectrometer. Details were given of an instrument and techniques suitable for the analysis of alloys. A report from the Kellex Corp. (109) described means of introducing solid samples into an ionization chamber. In one, the sample n-as deposited on a metal tape that passed through a series of vacuum locks. A model was built and tried with some success but not in conjunction with a mass spectrometer. A design was also given of a possible method of inserting through multiple locks a filament or furnace for vaporizing solid samples. Shepherd (1’76)has discussed the reproducibility and the accuracy of the mass-spectrometric method of analyzing a standard sample of a carbureted 15 ater gas. A comparison was also made (175) of the analysis of the same standard sample by mass spectrometric and by chemical methods. The accuracy and the precision of analysis of light hydrocarbon mixtures were discussed by Starr and Lane (187). Conclusions vere drax-n concerning the relative merits of mass spectrometric, ultraviolet, infrared, low temperature distillation, and chemical methods. MASS MEASUREMENT
The work on the measurement of packing fractions which in the past has been associated with the names of .4ston, Bainbridge, Dempster, Alattauch, and others was interrupted during World War I1 and this field has only recently grown in activity with the completion of instruments t h a t have been under construction for the past few years. Duckvorth and his coworkers have reported measurements on many elements in the heavier mass range with their Dempster-type instrument (51-58, 186). Xier and his Minnesota group have reported exceptionally fine results using their n e a method in which the ion beam is detected electrically (40, 79, 141, 166). Mattauch and his associates have increased the resolution of the Mattauch-Herzog type of instrument and have so greatly improved their techniques t h a t they have been able to report very good progress in improving on their earlier excellent measurements. Ewald has reported new measurements of many doublets and mass values through mass 40 ( 6 4 , 67). The Japanese school has been active in improving-the resolution of the Bainbridge-Jordan type of instrument as evidenced in the recent communication of Ogata and Matsuda (145). Bainbridge discusses the isotopic weight of helium ( 4 ) and Hays,
29 Richards, and Goudsmit (83) report measurements with their time-of-flight instrument. ISOTOPIC ABUNDANCE
Discrimination by the mass spectrometer has always been a problem in the determination of the true relative abundance of the isotopes in a given sample. Many papers in the past have discussed the causes of these discriminations and recommended techniques for minimizing their effects. S i e r (138) has described a method of measuring the relative abundance of isotopes, in which the discrimination in his apparatus was evperimentally determined by calibration with known synthetic mixtures of the previously separated isotopes of an element. Probably the most important element which he studied was oxygen and his results provide the most accurate value of the constant of conversion from the physical to the chemical scale of atomic weights. This work also re-emphasizes the effect on the conversion factor of the variations in the abundance of the isotopes of oxygen from different sources. D a t a on the abundances of the isotopes as well as the variations of these in nature have been increased by the research of many workers (1, S, 19, 39, 78, 82, 85, 94, 118, 119, 122,139,148,151,172,181,182, 198,200, Sol+, 208). The authors have been much interested in a paper by Wahl (213) ivhich only recently came to their attention. This describes a hfattauch-Herzog instrument and its application to the study of the age of various minerals. Although this work appeared long before the period covered by this survey, it is included now because this description of a Mattauch-Herzog inetrument appeared in a journal unfamiliar t o many readers. NUCLEAR PHYSICS STUDIES
The use of the mass spectrometric method for the separation of isotopes has been described in four publicatione (12, 43,106, 107). .4large number of papers give an account of the research on isotopes separated in this manner and others relate the success in identifying the products of nuclear reactions while providing a means of studying nuclear processes (6, 11, 93, 95-97, 106, 114, 116,l~4,168,162-164). REVIEWS
Since the appearance of the previous bibliography ( 1 7 7 ) , a surprising number of general review papem have appeared in print (SO, 36, 63, 74, 90, 112, l S 4 , 131, 135, 136, 156, 257, 167, 177, 199, 205, e l l ) . For the most part, these have stressed chemical and isotopic analysis. BIBLIOGRAPHY
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