Mass Spectrometer—Electron Spectrometer: Exchange Interaction

FOCUS Mass Spectrometer—Electron Spectrometer:

Exchange Interaction

Victor L. Talrose Institute of Energy Problems of Chemical Physics Leninsky Prospect 38 B-334, Moscow 117829 Russia

Gennadij V. Karachevtsev and Igor A. Kaltashov1 Moscow Institute of Physics and Technology Institutsky Pereulok 9 Dolgoprudny, Moscow Region 141700 Russia

Both mass spectrometry and electron spectrometry are analytical methods based on ionization processes and/or interactions of charged particles with matter. In both cases ionization is produced by electron impact, photon impact, or interactions of electrons or photons with excited atoms. The charged particles of interest may be produced either by interactions in the gas phase or with a surface. The fingerprint of a molecule studied in MS is the set of ions characteristic of the molecule. The masses and relative intensities of the ions produced during ionization give information on sample composition and molecular structure. J. J. Thompson, who invented charged-particle mass measurement, was the first to recognize the great importance of MS for analytical chemistry (1). 0003-2700/92/0364-401 A/$02.50/0 © 1992 American Chemical Society

The end of the Cold War h a s meant the opening of normal int e l l e c t u a l d i s c o u r s e a n d exchange between scientists in the former Soviet Union and those in the United States as well as other Western countries. Each group is interested in learning what the other has been doing for the past 40 years and who the players are in each speciality area. In this FOCUS article Victor Talrose, one of Russia's leading physical m a s s spectrometrists, and his co-authors touch on the synergism of mass and electron spectrometers, the interrelation of physical and analytical chemistry, and the interp l a y of Soviet a n d W e s t e r n science. Gennadij Karachevtsev was Talrose's Ph.D. student, and Igor Kaltashov was a student in Karachevtsev's laboratory. Catherine Fenselau Associate Editor, Mass Spectrometry

In addition to important applications in physics, MS is used widely in analytical chemistry, chemical kinetics, and chemical thermodynamics. MS has played a significant role in investigations of the kinetics and

thermodynamics of processes involving charged particles (2, 3).

Analysis of ion energies in MS The analysis of ion energies by MS can provide information about structures and/or energy states of massselected ions. Techniques that have been used for this purpose include kinetic energy gain/loss spectroscopy (4-6), mass ion kinetic energy (MIKE) spectroscopy (7), ion collision spectroscopy (4), and translational energy spectroscopy (TES) (8). A powerful new method for the determination of ion structures is coulomb explosion imaging (CEI) (9). In this technique, an accelerated molecular ion is passed through a thin solid film, which rapidly (in 10~ 16 s) strips away the valence electrons of the ion, thereby initiating a fast dissociation process termed a "coulomb explosion." By measuring the relative momenta of atomic fragment ions, their trajectories can be traced backward to deduce initial spatial positions before the explosion. Kinetic energy analysis of ions allows the possibility of selectively detecting only atomic ions. This method was used to selectively detect Yb ions that were obtained for the first time using high-resolution accelerator MS 1 Current address: Department of Chemistry and Biochemistry, University of Maryland Baltimore County, Baltimore, MD 21228

ANALYTICAL CHEMISTRY, VOL. 64, NO. 6, MARCH 15, 1992 · 401 A

FOCUS (AMS) in the presence of intense mo­ lecular interferences (10). Methods exist for ion energy mea­ surements based on mass spectral peak shapes and on retardation or deflection of ions by an applied elec­ tric field. Applications include mea­ surements of gas temperatures and translational energies of fragment ions, secondary ions produced in i o n molecule reactions (11, 12), and ions from superelastic collisions (13). The measurement of kinetic energies of the fragment ions produced in strong electric fields has been used to study the kinetics of ion decay (14-20). In analytical MS, ion kinetic en­ ergy filtering with retarding poten­ tials in the detection system pro­ duces a much cleaner mass spectrum and increases resolution (21). Electron spectroscopy In electron spectroscopy molecules are characterized by the energy spec­ trum of electrons detached by irradi­ ation or by the collision of particles with gaseous or solid targets. This energy spectrum provides informa­ tion about the electron energies of atomic and molecular orbitals, the electronic and vibrational levels of ions, and the energy levels of elec­ trons in solids. Recently the analyti­ cal applications of electron spectros­ copy have been extended (22-24). In photoelectron spectroscopy a monoenergetic beam of photons of energy hv is collided with sample molecules. Electrons may be removed from any molecular orbital with elec­ tron energy 7i; which is less than the photon energy. The translational en­ ergy Ε of the resulting electron is ex­ pressed as E = hv-Ii

(1)

The energy of the molecular orbital can be determined by energy analy­ sis of the photoelectrons released. Another variant of photoelectron spectroscopy uses an energy analyzer to transmit only electrons of a single energy. Usually the transmission en­ ergy is chosen to be at near-zero en­ ergy so t h a t only "threshold" elec­ trons are detected. The spectrum is then obtained by varying the energy of the ionization photons. Combining mass spectrometers and electron spectrometers The block diagrams of both electron and m a s s spectrometers are very similar. These devices operate at high vacuum and have a source of ionization and an ionization cham­ ber. Because they have similar charged-particle analyzers and data

acquisition and processing systems, it is possible that they can be com­ bined. For example, it h a s been very fruitful to merge mass spectrometric a n d electron s p e c t r o m e t r i c t e c h ­ niques in one installation for the study of solid surfaces. The pumping system, vacuum chamber, samplehandling system, and computerbased data acquisition and process­ ing systems are jointly used. The cost and dimensions of such an installa­ tion are comparable to those of each separate component. Such multitechnique systems—for example, com­ bining X-ray photoelectron spectros­ copy (XPS or ESCA), scanning Auger microprobe (SAM), secondary ion MS (SIMS), and ion scattering spectros­ copy (ISS)—became available com­ mercially in the mid-1980s (25). At least one combined mass spectrometric/electron spectrometric in­ strument has been developed (26). Both electron transmission spectros­ copy (ETS) and dissociative electron attachment MS (DAMS) have been possible. The ETS technique takes advantage of the strong dependence of the electron-molecule scattering cross sections associated with a reso­ nance process. On the other hand, DAMS measures negative ion cur­ rent as a function of the incident electron beam energy. These meth­ ods provide important information about kinetic and thermochemical parameters as well as the electron structure of the negative ions. In some cases mass spectrometers have been used as electron spectrom­ eters with simple changes in the op­ eration of a magnetic m a s s spec­ t r o m e t e r (27). In such cases, the magnetic field had to be reduced so that the mass analyzer could trans­ mit electrons, and a Hall detector was used to regulate the magnetic field. A high-efficiency detector was required, and the deflection tech­ nique was used to measure the ki­ netic energy of the charged p a r t i ­ cles. Figure 1 presents the results from an SF 6 /air mixture studied at 10~ 14 Torr u n d e r continuous ionization (28). The initial kinetic energies of the charged particles are propor­ tional to the squared fwhm of the ap­ propriate curves. The initial kinetic energies of F~ and SF4 fragments are very close to each other, but they are many times smaller t h a n those of electrons. The asymmetrical shape of the electron curve may include not only secondary electrons produced through the ionization of gas mole­ cules but also electrons produced

402 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 6, MARCH 15, 1992

Figure 1. Dependence of electron, F~, and SF 4 ion currents on deflecting voltage in a SF6/air mixture. through secondary electron emission off the surfaces of the ionization chamber. In addition, it is possible to detect not only the charged particles escap­ ing the ionization chamber but also those produced outside the chamber as a result of ion decay. Figure 2 pre­ sents the electron current as a func­ tion of acceleration voltage in an ex­ p e r i m e n t in w h i c h t h e S F 6 / a i r mixture is continuously ionized at a pressure of 1.5 Torr (28). The spec­ t r u m contains two distinguishing features: a narrow peak that corre­ sponds to electrons escaping the ion­ ization chamber and a wider peak t h a t corresponds to electrons pro­ duced outside the chamber by elec­ tron attachment from SFë ions S F i + M -* SF 6 + e- + M

(2)

This i m p o r t a n t process is u n d e r study. Mass spectrometers have also been used to obtain spectra of threshold electrons formed as a result of electron interactions with molecules e~ + AB -^ AB* + eô

(3)

To detect low-energy electrons it has been necessary to add molecules for which the cross section of electron attachment has a narrow peak at nearzero energy. For example, slow electrons are very effectively attached to SF 6 molecules e 0 + SF 6 -* S F 6

(4)

The cross section of electron attachment to S F 6 molecules has a maximum at zero energy and sharply dec r e a s e s w i t h i n c r e a s i n g electron energy (fwhm = 0.03 eV). When the energy of the electrons introduced into the ionization chamber equals an energy level in the molecule, the electron will transfer most of its energy to the molecule

troduced into the ionization chamber of a photoionization mass spectrometer (31). The dependence of SFg ion current on the ionization photon energy was measured while the processes in Equations 5 and 6 took place in the ionization chamber hv + M -> M + + e~ e" + S F e -» S F 6

(5) (6)

Each ionization threshold corresponds to an appropriate peak in the SFg ion current. This technique for measuring threshold photoelectron spectroscopy by electron attachment (TPSA) was first applied to the study of acetone (31) and subsequently extended to Ar, Xe, N 2 , CO, and C 2 H 2 (32-34). Under low pressure conditions one may increase the efficiency of slow e l e c t r o n a t t a c h m e n t by u s i n g a charged-particle magnetic trap (35). At low magnetic fields only slow electrons are retained in the trap while SFg ions escape the ionization chamber. In TPSA there is a possibility of producing spurious SFg peaks by processes involving excited atoms Xe* + SF 6 -> S F 6 + Xe +

Figure 2. Dependence of electron current on acceleration voltage (Vacc) obtained in a SF6/air mixture. AVacc= l/ a o c -2.5kV

and be readily attached. When S F e is the target, attachment will produce SFg. Information on the molecular energy level is obtained by detecting the SFg ion current as a function of electron beam energy (29). An analogous method has been used to study energy degradation of fast electrons in gases at high pressures (30). The relative fraction of t h e r m a l i z e d electrons was determined by monitoring the negative ion current of the acceptor of lowenergy electrons. Studies with photoionization Photoionization methods provide the highest energy resolution. In a typical experiment, a mixture of molecules of interest M and S F e was in-

(7)

Spurious peaks may also be obtained by means of slow electrons produced by interactions of photons or electrons with the walls of the ionization chamber. On the other hand, the detection of such ions may produce imp o r t a n t information about excited particles or about these surfaces. For example, TPSA was applied to the detection of slow photoelectrons escaping platinum and silver surfaces (36) to obtain information on the distribution of electron energy levels in the metals (37). In addition to the "chemical" detection method described above, there are other methods for threshold electron detection, such as cylindrical and semispherical electrostatic analyzers (38, 39). A simple and effective method for slow electron detection included line-of-sight steradiancy analyzers (40, 41). Photoelectrons are accelerated by a uniform electric field through collimating slits. The electrons with zero initial energy receive a velocity perpendicular to the plane of the collimating slits and are therefore transmitted. The electrons with higher initial translational energy usually have a sizable velocity component parallel to the plane of the collimating slits and therefore do not pass t h r o u g h the collimating slits. The use of steradiancy analyzers in MS permits discrimination against

fragment ions that have greater than t h e r m a l t r a n s l a t i o n a l energy. The r e s u l t is a m a s s s p e c t r u m w i t h smaller fragment peaks and more abundant parent ions. By taking advantage of such discrimination effects, Taranenko and Kobelyansky (42) were able to produce a mass spectrum from w-eicosane in which the parent ion had the highest relative abundance. This instrumentation can simplify the interpretation of the mass spectra of complex mixtures. Some years ago Karachevtsev and Marutkin (43, 44) described another method for obtaining mass spectra with reduced fragmentation intensities. The method was based on the ion current dependence of fragment ions (usually formed with greater translational energy), which differs from that of thermal molecular ions as a function of deflecting voltage. Ions that have small initial translational energies are easily deflected, whereas fast fragment ions are not so strongly deflected. The result is that groups of fast and slow ions of the same masses may be separated. For example, Figure 3 shows the dependence of the ion current for mass 32 as a function of deflecting voltage in an SF 6 /air mixture (28). It is possible to s e p a r a t e the peak corresponding to the thermal molecular 0 2 ions (narrow peak) and the peak representing fragment S + ions that have acquired extra energy (broad peak). This method of mass spectral analysis may be useful for measuring the neutral composition of a gas discharge plasma t h a t contains both atoms and molecules. Indirect analyzers equipped with non-line-of-sight trajectories have also been used (45, 46). Weak electric fields are used to select only elec-

Figure 3. Dependence of ion current (M = 32) on deflecting voltage obtained in an SF6/air mixture. The solid line indicates experimental data; dashed lines indicate the contributions from the separated ions.

ANALYTICAL CHEMISTRY, VOL. 64, NO. 6, MARCH 15, 1992 · 403 A

FOCUS t r o n s of low e n e r g i e s . A v e r y h i g h t r a n s m i s s i o n efficiency w a s f o u n d for t h e s e a n a l y z e r s , w h i c h a p p e a r to be u s e f u l for d i s t i n g u i s h i n g slow a n d fast i o n s . T h e m a s s s p e c t r a l d e t e c t i o n of H~ fragment ions with near-zero t r a n s lational energy formed in t h e disso­ ciative a t t a c h m e n t process e~ + H 2 - » H " + H

(8)

can be used to m e a s u r e concentra­ t i o n s of H 2 m o l e c u l e s i n v a r i o u s v i ­ b r a t i o n a l s t a t e s (47). T h e s e n s i t i v i t y of t h i s m e t h o d is 1 0 1 1 c n r 3 for H 2 in t h e g r o u n d v i b r a t i o n a l s t a t e (v = 0) a n d i n c r e a s e s t o 5 χ 1 0 5 c m - 3 for h i g h v i b r a t i o n a l s t a t e s (v > 5). T h e s p e c i a l c o n f i g u r a t i o n of t h e e l e c t r o s t a t i c p o ­ t e n t i a l in t h e ion s o u r c e p e r m i t s effi­ c i e n t collection of slow n e g a t i v e i o n s only (47). S u c h e l e c t r o d e c o n f i g u r a ­ t i o n s i n t h e ion source m a y be useful for p r o d u c i n g s p e c t r a w i t h s m a l l e r f r a g m e n t ion p e a k s b y d i s c r i m i n a ­ tion against fragment ions t h a t have higher translational energies. Thus s o m e c o m p o n e n t s of e l e c t r o n s p e c ­ t r o m e t e r s m a y be u s e d i n m a s s s p e c ­ t r o m e t e r s a n d vice v e r s a .

Photoionization MS/ photoelectron spectroscopy To s t u d y u n i m o l e c u l a r ion d i s s o c i a ­ tion processes and ion-molecule r e ­ a c t i o n s a t specific i n t e r n a l e n e r g i e s , coincidence M S can be combined w i t h p h o t o e l e c t r o n spectroscopy. T h e m a s s spectrometer and the electron spectrometer share an ionization c h a m b e r t h a t p e r m i t s d e t e c t i o n of both the photoelectron and a corre­ sponding photoion. The charged p a r ­ ticles a r e d e t e c t e d by photoion— p h o t o e l e c t r o n coincidence ( P I P E C O ) . When threshold photoelectrons are d e t e c t e d , t h e i n t e r n a l e n e r g y of t h e r e a c t a n t m o l e c u l a r ion is d e t e r m i n e d b y t h e difference b e t w e e n t h e e n e r g y of t h e i o n i z a t i o n p h o t o n a n d t h e m o ­ lecular ionization potential. O n e m a y o b t a i n r e a c t a n t i o n s of selected electronic and vibrational s t a t e s b y v a r y i n g t h e e n e r g y of t h e i o n i z a t i o n p h o t o n s (48-56). In this c a s e t h e c o m b i n a t i o n of m a s s s p e c ­ trometer and electron spectrometer in o n e i n s t a l l a t i o n p r o d u c e s a q u a n ­ t i t a t i v e l y n e w device t h a t is m o r e powerful t h a n its s e p a r a t e compo­ nents. The PIPECO method has been s h o w n to d e c r e a s e t h e b i a s of t h e r ­ modynamic characteristics (52-54). Used as a pulsed method, P I P E C O p r o v i d e s good s e n s i t i v i t y a n d r e s o l u ­ t i o n a n d is p r o m i s i n g for t h e s t u d y of radicals coexisting with other molec­ u l a r s p e c i e s (54).

A c o m b i n a t i o n of r e s o n a n c e enhanced multiphoton ionization photoelectron spectroscopy/MS can b e u s e d to s t u d y selectively excited v i b r a t i o n a l m o d e s of p o l y a t o m i c c a t ­ ions, a n d t h e s e m o d e s p l a y different roles i n c o n t r o l l i n g t h e collision d y ­ n a m i c s (51). T h i s c o m b i n e d i n s t r u ­ m e n t is i n d e e d m o r e powerful t h a n t h e s u m of i t s p a r t s . The view t h a t seemingly separate p h y s i c a l c h e m i c a l t e c h n i q u e s c a n be combined w h e n their i n s t r u m e n t a l r e q u i r e m e n t s are compatible should c o n t i n u e t o l e a d t o n e w discoveries about atomic and molecular energet­ ics a n d w i l l p r o v i d e t h e b a s i s for powerful n e w a n a l y t i c a l tools. We gratefully acknowledge Jeffrey P. Honovich for his assistance in the preparation of the manuscript.

References (1) Thomson, J. J. Rays of Positive Electricity and Their Application to Chemical Analysis; Longmans: London, 1913. (2) Talrose, V. L. Adv. Mass Spectrom. 1980, 8A, 147. (3) Futrell, J. H. Gaseous Ion Chemistry and Mass Spectrometry; Wiley: New York, 1986. (4) Collision Spectroscopy; Cooks, R. G., Ed.; Plenum Press: New York, 1978. (5) Aparina, E. V.; Balakay, Α. Α.; Markin, M. I.; Talrose, V. L. Khim Vys. Energ. (Sov.) 1982, 16, 195. (6) Jonathan, P.; Hamdan, M.; Brenton, A. G.; Willett, G.J. Chem. Phys. 1988,119, 159 (7) Reid, C. J.J. Phys. B:At. Mol. Phys. 1990, 23, 2783. (8) Hamdan, M.; Brenton, A. G. In Physics and Ion Impact Phenomena; Springer Se­ ries in Chemical Physics; Springer: Ber­ lin, 1991; Vol. 54, Chapter 6. (9) Vager, Z.; Naaman, R.; Kanter, E. P. Science 1989, 244, 426. (10) Litherland, A. E.; Kilius, L. R.; Garwan, Μ. Α.; Nadean, M. J.; Zhao, X. L. /. Phys. Β 1991, 24, L233. (11) Talrose, V. L. Chemical Effects of Nu­ clear Transformations; International Atomic Energy Agency: Vienna, Austria, 1961; p. 103. (12) Talrose, V. L.; Karachevtsev, G. V. In Reactions under Plasma Conditions; Venugopalan, M., Ed.; John Wiley & Sons: New York, 1971; Vol. II, p. 35. (13) Talrose, V. L.; Vinogradov, P. S.; Larin, I. K. In Gas Phase Ion Chemistry; Bowers, M. T., Ed.; Academic Press: New York, 1979; Vol. 1, p. 305. (14) Becky, H. D. Z. Naturforschung 1961, ISA, 505. (15) Becky, H. D. Field Ionization Mass Spectrometry; Pergamon: Elmsford, NY, 1971. (16) Derric, P. J.; Falick, A. M.; Burlingame, A. L. /. Am. Chem. Soc. 1972, 94, 6794. (17) Karachevtsev, G. V.; Talrose, V. L. Kin. Ratal. (Sov.) 1963, 4, 923. (18) Karachevtsev, G. V.; Talrose, V. L. Kin. Katal. (Sov.) 1967, 8, 5. (19) Ottinger, C. Z. Naturforschung 1967, 22a, 20. (20) Ottinger, C. Z. Naturforschung 1972, 27a 293. (21) Feng,' R.; Konishi, Y. Abstracts of Pa­

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pers, 12th International Mass Spectrom­ etry Conference, Amsterdam, The Neth­ erlands, 1991; p. 298. (22) Vilesov, F. I.; Kurbatov, B. L.; Terenin, A. N. Dokl. Akad. Nauk SSSR (Sov.) 1961 138 1329 (23) Baker, A. D.; Betteridge, D. Photoelec­ tron Spectroscopy: Chemical and Analytical Aspects; Pergamon: Oxford, 1972. (24) Carlson, T. A. Photoelectron and Auger Spectroscopy; Plenum: New York, 1977. (25) Product Bulletin A314-0282, Kratos Analytical I n s t r u m e n t s (Manchester, U.K.), 1982. (26) Modelli, Α.; Foffani, Α.; Scagnolari, F.; Jones, D. Chem. Phys. Lett. 1989, 163, 269. (27) B a b a e v , A. P.; K a l t a s h o v , Ι. Α.; Karachevtsev, G. V.; Marutkin, A. Z. Instrum. Exp. Tech. (Sov.) 1990, 4, 200. (28) Kaltashov, Ι. Α.; Karachevtsev, G. V. unpublished results. (29) Compton, R. N.; Huebner, R. H. Adv. Radiât. Chem. 1970, 2, 281. (30) Gregor, I. K.; Guilhaus, M. Int. J. Mass Spectrom. Ion Processes 1984, 56, 167. (31) Karachevtsev, G. V.; Potapov, V. K ; Sorokin, V. V. Dokl. Akad. Nauk SSSR (Sov.) 1972, 206, 144. (32) Ajello, J. M.; Chutjian, J. M. /. Chem. Phys. 1976, 65, 5524. (33) Chutjian, J. M.; Ajello, J. M. /. Chem. Phys. 1977, 66, 4544. (34) Ajello, J. M.; Chutjian, J. M. /. Chem. Phys. 1979, 71, 1079. (35) Karachevtsev, G. V.; Lipey, M. M.; Potapov, V. K. Khim Vys. Energ. (Sov.) 1975, 6, 487. (36) Karachevtsev, G. V.; Potapov, V. K ; Sorokin, V. V. Opt. Spectrosc. (Sov.) 1974, 35, 960. (37) Karachevtsev, G. V. Opt. Spectrosc. (Sov.) 1985, 59, 202. (38) Villarejo, D.; Herm, R. R.; Inghram, M. G.J. Chem. Phys. 1967, 46, 4995. (39) King, J. C. In Electron-Molecule Scatter and Photoionization; Proceedings of the International Symposium; Burke, P. G.; West, J. B., Eds.; Plenum: New York, 1988; p. 99. (40) Spohr, R.; Guyon, P. M.; Chupka, W. Α.; Berkowitz, R. Rev. Sci. lustrum. 1971, 42, 1872. (41) Karachevtsev, G. V.; Lipey, M. M.; Potapov, V. K. Instrum. Exp. Tech. (Sov.) 1976, 6, 141. (42) Taranenko, L. Α.; Kobelyansky, P. V. /. Tech. Phys. (Sov.) 1989, 50(10), 195. (43) Karachevtsev, G. V.; Marutkin, A. Z. Instrum. Exp. Tech. (Sov.) 1979, 6, 119. (44) Karachevtsev, G. V.; Marutkin, A. Z. Instrum. Exp. Tech. (Sov.) 1981, 2, 173. (45) Peatman, W. B.; Kasting, G. B.; Wil­ son, D. J. /. Electron. Spectrosc. 1975, 7, 233. (46) Tanaka, K.; Kato, T.; Koyano, I. /. Chem. Phys. 1986, 84, 750. (47) Popovic, D.; Cadez, I.; Landau, M.; Pichou, F.; Schermann, C ; Hall, R. I. Measurement Science and Technology 1990, 1, 1041. (48) Jochima, H. W.; Ruhl, E.; Baumgartel, Μ. Z. Naturforschung 1989, 44B, 13. (49) Koyano, L; Tanaka, K.; Ibariki, K. Proceedings of the International Symposium on Advanced Nuclear Energy Research: Near-Future Chemistry in the Nuclear En­ ergy Field, J a p a n Atomic Energy Re­ search Institute: Tokyo, 1989; p. 341. (50) Golovin, A. V.; Akopian, M. E.; Reingang, L. M.; Chistyakov, A. B. Khim. Vys. Energ. (Sov.) 1989, 23, 387. (51) Yang, B.; Chui, Y.; Orlando, T. M.; Anserdon, S. L. Abstracts of Papers, SASP '90: Symp. Atomic and Surface Physics, Obertraun, 1990, p. 276.

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Supercritical Fluid Extraction/ Chromatography Monday-Thursday, May 11-14, 1992 Virginia Tech · Blacksburg, VA

An intensive 4-day short course that will provide you with practical lab experience in the techniques and instrumentation involved in SFC/SFE Victor L. Talrose (left) is director of the Institute of Energy Problems of Chemical Physics and professor and former dean of the Moscow Institute of Physics and Tech­ nology. He holds an M.S. degree (1947) and a Ph.D. in physics (1952) from Mos­ cow State University, as well as a D.Sc. degree in chemistry (1962) from the Insti­ tute of Chemical Physics of the Academy of Sciences. He was elected to the Russian Academy of Sciences in 1968 and has written more than 400 papers and four monographs. His primary fields of interest include chemical physics, radiation chem­ istry, MS, chemical lasers, atmospheric chemistry, and the ecological conse­ quences of energy. He discovered ionmolecule reactions of organic substances with the CH*5 ion. Gennadij V. Karachevtsev (right) is a professor in the department of molecular and chemical physics at the Moscow Insti­ tute of Physics and Technology. He re­ ceived his M.S. degree (1961) and his Ph.D. (1966) from the institute. His re­ search interests include kinetics and ther­ mochemistry of gas-phase ion and elec­ tron processes, MS, and electron spectrometry.

S

'even Key Ways You'll Benefit from Attending This Course: /. 2. 3. 4.

Learn state-of-the-art techniques for performing SFE and SFC Learn to interpret SFC and SFE data Discover why SFE offers advantages over conventional extraction Know which SFC and SFE strategies to use when your analyte will not dissolve in

co 2 5. 6.

7.

Obtain guidelines for column selection Gain hands-on experience working with chromatographs, column detectors, and extraction devices Understand the limitations of SFE and SFC

Instructor: Larry T. Taylor, Professor of Chemistry, Virginia Tech

Register T o d a y ! E n r o l l m e n t In this popular course is strictly l i m i t e d t o 3 0 participants.

To register or to obtain more Information about this unique short course, call the Continuing Education Short Course Office at (800) 227-5558 (TOLL FREE) or (202) 872-4508. Or, send in the coupon below to request a free descriptive brochure.

Please send me a free brochure on the ACS Short Course, Supercritical Fluid Extraction/Chromatography to be held May 11-14, 1992, in Blacksburg, VA. Name Title Organization

Igor A. Kaltashov received his M.S. degree (1989) from Moscow Institute of Physics and Technology, where he studied ion pro­ cesses with MS. He is currently a graduate student in the department of chemistry and biochemistry at the University of Maryland Baltimore County.

Address

City. State, Zip Mail To: American Chemical Society, Dept. of Continuing Education, Meeting Code VPI9205, 1155 Sixteenth Street, N.W., Washington, DC 20036

ANALYTICAL CHEMISTRY, VOL. 64, NO. 6, MARCH 15, 1992 · 405 A