Anal. Chem. 7909. 61. 238R-243R (G35) Kramer. E.; Koppelmann, J. Polym. Degrad. Stab. 1986, 16, 261-275. (G36) Farr, M.; Harrison, I . J. Polym. Sci., Part C: Polym. Len. 1988, 24, 257-261. (G37) Basan, S.;Guven, 0. Thermochim. Acta 1986, 106, 169-178. (G38) Jain, R. K.; Lal, K.; Bhatnagar, H. L. Eur. Polym. J. 1986, 2 2 , 993- 1000. (G39) Roman, J. S.:Madruga, E. L.; Pargada, L. Polym. Degrd. Stab. 1987, 19. 161-176. (G40) Nagpal. A. K.; Mathur, G. N. Ind. J. Tech. 1987, 2 5 , 272-275. (G41) Steiner. G.; Koppelmann, J. Polym. Degrad. Stab. 1987, 19, 307-314. (G42) Serageldin, M. A.; Wang, H. Thermochim. Acts 1988, 125, 247-259. (G43) Crossland, 8.; Knight, G.; Wright, W. Br. Polym. J. 1988, 18, 371-375. (G44) Hay, J. N.; Kemmish, D. J. Polymer 1987, 2 8 , 2047-2051. (G45) DiChiara, R.; Langer, H. Proceedings of the Slxteenth North American Thermal Analysis Society Conference, Washington, DC, Paper No. 91, pp 462-467. (G46) Mazich, K.; Samus, M.; Killgoar, P.; Plummer, H. Rubber Chem. Techno/. 1986, 5 9 , 623-633. (G47) Class, S. D.; McFaddin, D. C.; Russel, K. E. J. Polym. Sci.. Part 8: Polym. Phys. 1967, 2 5 , 1057-1069. (G48) Rueda, L. I.; Anton, C. C.: Rodriguez, M. C. T. Angew. Makromol. Chern. 1988, 160, 29-39. (G49) Plazek, D. J.; Rosner, M. J.: Plazek, D. L. J. Polym. Sci., Part 8: Polym. Phys. 1988. 2 6 , 473-489. (G50) Hartmann, B.; Duffy, J. V.; Lee, G. F.; Baker, E. J. Appl. Polym. Sci. 1968, 3 5 , 1829-1852. (G51) Qian, 8 . ; Wu, 2 . ; Yang, P.; Qin. J. I n t . Polym. Proc. 1987, 1 , 123-129. (G52) Petermann, J.; Rieck, U. J. Polym. Sci., Part 8: Po/ym. Phys. 1987, 2 5 , 279-293. (G53) Chuah, H.; Lin, J.; Porter, R. Macromolecules 1988, 19, 2732-2736. (G54) Sun, D. C.; Magill, J. H. Polym. Prep. 1987, 2 8 , 351-353.
(G55) Roy, S. K.; Kyu, T.; Manley, R. S. J. Macromolecules 1968, 2 1 , 499-504. (G56) Pasztor Jr, A. J.; Dibbs, M. G.; Seltz, J. T. Proceedings of the Sixteenth North American Thermal Analysis Society Conference, Washlngton, DC, Paper No. 87, 437-442. (G57) Sun. D.: Magill, J. Proceedings of the Seventeenth North Amerlcan Thermal Analysis Society Conference, Lake Buena Vista, FL, Paper No. 24, 99-109. (G58) Cheng, S.;Wunderlich. B. Macromolecules 1987, 2 0 , 1630-1637. (G59) Silvestre, C.; Cimmino, S.;Karasz, R. E.; MacKnight, W. J. J. Polym. Sc!., Part B : Polym. phvs. 1987, 2 5 , 2531-2540. (G60) Atanassov, A. M. Polym. Bull. 1987. 17. 445-451. (G61) Huang, Y. H.; Sergeldln, M. A. Thermochim. Acta 1987, 112, 161-169. (G62) Cheng, S. Z. D.; Wu. 2. W.; Wunderlich, B. Macronw/ecules 1987, 2 0 , 2802-2810. (G63) Mijangos, C.; Martinez, G.: Millan, J.-L. Makromol. Chem. 1988, 189, 567-572. (G64) Klllc, S.; Morcol, T.; Summers, J.; McGrath, J.: Proceedings of the Sixteenth North American Thermal Analysis Society Conference, Washington, DC, Paper No. 55, pp 269-275. (G65) Hall, H.; Ceckler, W.; Thompson, E. J. Appl. Polyrn. Sci. 1987, 3 3 , 2029-2039. (G66) Harrison. I. J. Therm. Anal. 1988. 3 1 . 875-881. (G67) Schouterden, P.; Groenickx, G.; Van der Heijden. 8.; Jansen, F. Polymer 1987. 2 8 . 2099-2104. (G68) Hutchinson, J. M.; Ruddy, M.; Wilson, M. R. Polymer 1988. 2 9 , 152-158. (G69) Flynn, J. H.;Levin, D. M. Thermochim. Acta 1988, 126. 93-100. (G70) Farr, M. P. Proceedings of the Seventeenth North American Thermal Analysis Society Conference, Lake Buena Vlsta, FL, Paper No. 31, pp 162-170. (G71)-Wleboldt, R. C.; Adams, 0. E.: Lowry, S. R.; Rosenthal, R. J. Amer. Lab. 1988, 20, 70, 72, 74, 76. ,
Rubber Anoop Krishen Materials Characterization, Analytical Services, T h e Goodyear Tire & Rubber Company,' Akron, Ohio 44305
This review covers methods for identification, characterization, and determination of rubber and materials in rubber. Literature that became available to the author between January, 1987,the end of the period covered by the last review in this series (I),and December 1988 is reviewed. Chemical Abstracts, RAPRA, and other abstracting services were utilized to a lar e extent by the staff of the Technical Information Services at goodyear to provide initial screening of published literature. Abbreviations recommended in ASTM Designation D1418-85 have been used. These are listed in Table I.
Table 1. Abbreviations Recommended by ASTM (2) for Rubbers
BR butadiene rubber CR chloroprene rubber EPDM terpolymer of ethene, propene, and a diene with the residual portion of unsaturated synthetic rubber EPM copolymers of ethene and propene IR isoprene synthetic rubber NR natural rubber SBR styrene-butadiene rubber SIR stvrene-isourene rubber
GENERAL INFORMATION A review article on identification of elastomers (3)described some of the simpler procedures including visual examination, specific gravity, flame tests, odor, and colorimetric tests. Another review focused on modern scientific methods (4)for identification, purity determination, and statistical analysis as applied to product uniformity. Methods for vulcanizate and filler analysis were reviewed (5) with relation to trends and problems in rubber analysis. This included a discussion of current instrumental techniques like integral multicomponent methods which showed the greatest potential. Digital image analysis electron microscopy, analysis of polymer blends, microanalysis, and modeling with two-dimensional Fourier transform as applied to analysis of rubbers were reviewed (6). Some of the nonconventional methods for rubbers that were described in a review (7) included trichromatic colorimetry
and electronic polarography. This review also discussed the use of these techniques in process control. Veith presented an overview (8)of the action on precision assessment currently being conducted in ASTM Committee D11 and ISO/TC-45. Details were given on the organization of interlaboratory programs needed to acquire the basic precision data. Precision of the methods used in IR spectroscopy, partition chromatography, and thermogravimetry was reviewed (9) from a quality assurance perspective. Reviews dealing with specific analytical techniques included thermal analysis by Sircar (IO),NMR spectroscopy by Heatley (11),analytical techniques for molecular weight determination (12),and gel permeation chromatography (13). A recent book by J. Mitchell as editor (14) entitled Applied Polymer Analysis and Characterization covers various aspects of polymer analysis and characterization. These include techniques, instrumentation, review of literature, chemical and physical methods for analysis of complex systems, state of the art chemical and physical techniques, determination of ad-
Contribution No. 662 from The Goodyear Tire & Rubber Company, Research Laboratory, Akron, OH 44305. 230 R
1989 American Chemical Society
RUBBER Anoop K h h . n received Wm Ph.D dagw lrom Wm Universw 01 PMSbUgh and Wm M.Sc. (Honours School) and Ihs E.%. (Honours School1 Wrws hom the UnkersnV 01 Punlab. He bind lh R e w r c h Divisbn 01 The W e a r Tire (L Rubber Company. A t ,on. OH. in 1963. He is cunenliy Seclbn Head In charge of the Materials CheraclerC 281bn Section in the AnaMical and Mater!-
CBI Chemistry and Rub&
ditives. determination of residual monomers, oligomers, moisture, and impurities, and multitechnique approach to problem solving, NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (NMRI A general treatment was devised for the I3C NMR spectral analysis of EPM (15). This was based on a computerized "synthetic approach" using first-order Markovian statistics, Monte Carlo chain generation, spectral prediction, and spectral simulation. This procedure simulated homopolymer and copolymer spectra of increasing complexity for various structural types and provided good results. Characterization of EPM was achieved with a two-dimensional NMR technique (16) which utilized I3C-'H shift correlation. This allowed a complete computer interpretation of the one-dimensional 'H NMR spectra even when the IH resonances are heavily overlapped. Both chlorobutyl and bromobutyl rubbers were shown to contain exomethylene type structue based on 'H and NMR analyses (17). A numerical and graphical method based on NMR data for the determination of cis-1,4, trans-1,4, and vinyl ratios in BR was reported (18). Cross polarization and magic angle spinning I3C NMR were used to detect changes in the spectra of BR as a function of cross-link density (19). Proton relaxation data and I3C cross polarizationfmagic angle spinning spectra of triblock SBR were examined over a wide temperature range (20). The results emphasize the desirability of the knowledge of the roton characteristics of heterogeneous systems when their I C CPfMAS spectra are to be interpreted. Structural changes occurring in y-irradiated NR were studied by solid-state '3c NMR, swelling measurements, and sol el analysis (21). It was reported that the structure of the irrziated NR was hetercgeneous, consisting of a mobile phase and a semirigid phase. Evidence of main chain scission was observed by the presence of resonance due to vinyl end groups. High-resolution solid-state I3C NMR was used to characterize sulfur-vulcanized NR (22). This information was claimed to provide further understanding of the relationship between the cross-link structure and physical properties. Cross-link structures and other structural modifications in accelerator-containing sulfur-vulcanized NR were studied by solid-state '3c NMR (23). Polysulfidic cross links, accelerator residue terminated polysulfides, few cyclic sulfides, and cistrans chain isomerization were ohserved. Some of the . .~ .. structures were also no14 in sulfur-vulcanized systeis withiii a n y accelerators (241. The nature of the NMR spectral hroadening was claimed to ariqe from the lack of molecular motion in the system due to an increase in chemical shift dispersion caused by the new structures formed during vulcanization. NR was isomerized either by dehydrobromination of hydrobrominated NR or by heating with butadiene sulfone (25).The '3c NMR speetra of the CH2 region was interpreted in terms of diad arrangements for which assignments were made by calculating chemical shifts according to three different published methods. I3C NMR intensity measurements showed that the elimination of HBr was a random process. The spin-echo images of cis-BR and smoked NR were examined to define the utility of commercially availahle magnetic resonance imaging equipment (26). Highly rubbery, bulk polymers of low glass transition temperature, and high chain mobility were the easiest to image. The formations of trace amounts of cyclic oligomers in the copolymerization of isoprene with isobutylene were studied ~
by MS and NMR (27). Two major products that were detected are l-isopropenyl-2,2,4,4-tetramethylcyclohexaneand another structurally related cyclohexane derivative. The increase in the molecular weight of an EPDM (Keltan 778) during ozonolysis in carbon tetrachloride was studied (28). NMR showed that the elastomer macromolecules contained vinyl and cyclic double bonds in the ratio of 4.661. Results of NMR analysis of polydienes showed evidence of steric hindrance of cis-dimethyl groups (29). NMR features directly relevant to block copolymers were presented with relation to various factors (30). Applications of solid-state NMR to the determination of the structure of cross-linked polymers, particularly in cure processes, were presented (31). Spinspin. spin-lattice, and rotating frame relaxation times were measured by pulsed NMR for several block copolymers of styrene with butadiene or isoprene (32). NMR measurements gave the volume fraction of the interface phase and the thickness of the interface was estimated from the size of the domain and its shape was observed by TEM. The curin of a phenolic resin by hexamethylenetetramine was followerfby NMR (33). The cure was shown to result in increased cross linking, with the bridging carbons originating from the curing a ent Intermediates involved in the curing process were i%entified.
INFRARED S P E C T R O S C O P Y (IR) IR spectroscopy in the 650-850-cm-l region was used to study the molecular structure of E P M s containing 37-40 mol 70 nronvlene~.(34). . The ratio of monomers was determined by micrwomputer-aided resolution nf the h r k d IR absorption maximum into 690. 722. 732, 752, and R l 5 cm-' spectral components. The use of IR internal reflection spectroscopy for the chararteri7ation of carbon black.reinforced EPDM was described (35). The composition and structure of carbon-black-filled rubbers was studied by IR analysis of the rubber pyrolyzates (36). Pyrolysis provided quantitation of the components while attenuated total reflection IR gave information about the structure of the rubbers at the surface of the compounds. The effect of degradation and imbedded particles was also studied. Fourier transform IR was used to obtain the rate of formation of cyclic imide in the reaction of maleic anhydride styrene copolymer with amine-terminated nitrile rubber or Nylon 11 (37). The lower temperature and lower molecular weight experimentally showed faster reaction and the reaction proceeded to a greater extent. The composition of a complex three-layer polymer laminate was determined by FT-IR microscopy (38).The microtomed film was examined under cross-polarized light as an aid to distinguish boundary areas. IR analysis of solution and el fractions of NR showed that hydrogen-bonded properties %+tween proteins and isoprene chains in each phase greatly affected their mechanical properties (39). These interactions were proposed to form physical cross links between polyisoprene chains. Combinations of spectroscopic and mechanical measurements were used to study the nature of the bonding, and it was suggested that the interactions involved both the protein and the lactone groups on the main chain. The structures of 20 commercial oils and plasticizers for rubbers were characterized by FT-IR (40). This information was used to allow plasticizer substitution. modification, and blending to achieve better performance.
THERMAL METHODS A kinetic evaluation method was presented for nonisothermal reactions measured with differential scanning calorimetry (DSC) (41). This method is applicable for studying kinetia of vulcanization of NR and is based on multiple linear regression analysis using a number of curve points in a selectable range of conversions. The kinetic data can be used to compute a reaction process under isothermal or adiabatic conditions. Thermal analysis of rubber compounds using DSC, TGA, and thermomechanical methods was described for quality assurance applications (42). Vacuum TCA with isothermal stepwise temperature prcgramming was used to provide precise measurement of oil content (43). This procedure uses the sample weight 1w and ANALYTICAL CHEMISTRY, VOL. 61, NO. 12. JUNE 15,
its first derivative versus time to show separation of oil from rubber and requires less than 1 h per sample. Applications of thermogravimetry for raw materials in coatings were described (44). This technique was used to quantitate chlorine in chlorinated rubbers and tin and zinc in organometallic compounds and for the identification of zinc chromates and phosphates. TG analysis of CR was conducted by initial pyrolysis of CR followed by oxidation in low-oxygen atmosphere where the CR residue is oxidized before carbon black ( 4 5 ) . This permits accurate determination of both CR and carbon black. DSC and TGA were used to evaluate the relative effectiveness of various commercial antioxidants and heat stabilizers in IR at 170 OC (46). The structure of swollen and unswollen networks of vulcanized BR was determined by DSC as the cross-link density and the average cross-link unit molecular weight correlated with the transition temperature of crystallization and melting as well as with the heat of melting (47). The number average interval of cross-link nodes, calculated from DSC cooling curves, accurately reflected network parameters such as average cross-link molecular weight and the degree of swelling. The interval of cross-link nodes depended on the vulcanization process, and DSC could determine the variation of swollen networks and follow the freezing process of a swelling agent in the network. The magnitude of the depression of the freezing point of a solvent in a swollen rubber vulcanizate depends on the cross-link density in both phases of a vulcanized blend (48). The degree of vulcanization in SBR, BR, and NR was determined by TGA of small samples swollen with toluene (49). This technique was used to detect vulcanization gradients within thin sections of tire treads and liners. DSC was utilized to determine the isothermal crystallization rate for CR (50). The optimum crystallization temperature was 5 "C. Direct injection enthalpimetric methods for determining residual unsaturation in both water- and hydrocarbon-soluble polymers were described (51). These methods are based on the heat of bromination of double bonds and are an improvement over earlier procedures. The relationship between Tg and molecular weight was evaluated for IIR in terms of the Gibbs-DiMarzio statistical mechanical theory and a comparison made of this approach with that of Fox and Flory (52). Polystyrene and its copolymers like SBR were studied by DTA and found to exhibit two exothermic peaks and one endothermic peak at 380 OC (53).
GEL PERMEATION AND SIZE EXCLUSION CHROMATOGRAPHY (GPC, SEC) SEC with silica-based columns was studied under highspeed and superspeed conditions (54). A high molecular wei ht polystyrene sample was resolved in 3 s. Improvements in cfetection with superspeed SEC were achieved by reducing sample dilution and base-line noise in the UV-visible detector (55). High-performance microcolumn SEC for polystyrene required only 1-mg standards to obtain the Mark-Kuhn-Houwink constants (56). The unique macromolecular compression effect or delayed GPC elution of high-molecular weight materials was observed with GPC-LALLS (57). The degradation of the standard was detected by the LALLS detector. The use of an on-line GPC system for the analysis of polymers and low molecular weight additives was described (58). Branched fractions in IR were determined by a combination of GPC and light scattering techniques (59). It was reported that the branched macromolecules led to deterioration of the service properties. An SEC system was outlined using multiple detection by LALLS and a concentration detector along with a differential viscometer (60). This combination of three detectors permits the determination of M,, M,, viscosity average molecular weight, and the Mark-Houwink constants. A viscosity detector was constructed and was incorporated directly within a differential refractive index detector for polymer analysis (61). This system allows the collection of data for universal calibration in SEC. Model calculations were presented to show that with GPC-LALLS only M , could be determined with acceptable accuracy (62). M , could also be determined with reasonable 240R
ANALYTICAL CHEMISTRY, VOL. 61, NO 12, JUNE 15, 1989
accuracy only for polymers with low dispersity. Information on GPC and polymer characterization using a photodiode array detector was presented for SBR, SIR, and EPDM (63). An automated data acquisition and analysis system was described for GPC using LALLS, differential refractometer, mass detector and a viscometer (64). A system of personal computer programs for data collection and analysis in GPC of polymers was presented (65). Apparent molecular weights of NR as determined by GPC were several times higher when polystyrene was used as a standard (66). A general method to correct molecular weights based on one standard to another was presented. This requires calibration curves for both standards on the same column.
ANALYSIS RELATED TO HEALTH AND SAFETY Volatile compounds released from rubber products a t high temperatures were identified (67). Forty-four rubber products used in contact with food-nipples, pacifiers, seals for pressure cookers, hoses, spatulas-and 29 products used in medical supplies-stoppers for medicine, catheters, and gloves-were tested. Nineteen compounds were identified among the volatiles by mass spectrometry. These included carbon disulfide, carbonyl sulfide, aldehydes, ketones, aromatic and chlorinated solvents, and siloxanes. Tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, and other accelerators of these types released carbon disulfide when the rubber articles were boiled in water. A series of 22 tests were suggested to test the admissability of rubber stoppers in sanitary applications (68). These included boiling in an aqueous glucose solution or in sodium bicarbonate solution (69) and physiochemical and spectrophotometric analysis of the stoppers and their leachates for metls, contaminants, and toxic compounds. The primary and secondary amines present in waste gases from rubber manufacture were quantitatied by passing 420 mL of the waste gas through a 100 mm long and 4 mm diameter glass tube filled with 0.35-0.50 mm glass beads coated with cobalt chloride (70). The distance of color change of the bead column from rose to blue was related to amine concentration. The amines were desorbed from the column by extraction with 10% potassium hydroxide and characterized by gas chromatography. The level of zinc ethylphenyldithiocarabamate and its decomposition products-ethylaniline, sulfur dioxide, and ethylphenyldithiocarbamic acid-were determined after extraction of rubber cured with this accelerator using water, 0.3% lactic acid, or 2% citric acid (71). Volatile nitrosoamines were determined in nipples and pacifiers by (a) soaking the sample overnight in dichloromethane in the presence of propyl gallate as an inhibitor of artifact formation with nitrosamines, (b) extraction with dichloromethane using a column extraction procedure, (c) distillation from aqueous alkaline solution, (d) extract of the aqueous distillate with dichloromethane and concentration using a Kuderna-Danish concentrator, and (e) final analysis by gas chromatography with thermal energy analyzer detection (72). The method is claimed to be accurate (90% recovery) and precise (f4.770 a t >9 ppb). Quantitation of N-nitrosobutylamine in neutral buffer extracts from rubber products was described (73). The extraction, cleanup, and concentration were achieved in a one-step procedure using CI8 cartridges followed by gas chromatography. Three porous polymer adsorbents Tenax TA, Chromosorb 102, and Chromosorb 103 were investigated for gas-phase trapping of volatile N-nitrosoamines followed by thermal desorption injected onto a gas chromatograph using a thermal energy analysis detector (74). Chromosorb 103 exhibited the best adsorbent characteristics for preconcentration. Tetramethylthiuram disulfide and o-toluylbiguanidine were determined by thin-layer chromatography of the extracts from rubber stoppers used with parenteral fluids (75). An injectable, water-soluble vitamin E product was examined for contaminants from rubber stoppers by using gas chromatography, gas chromatography/mass spectrometry, high-performance liquid chromatography, and inductively coupled plasma emission spectroscopy (76). Dibutylamine, dimethylcyclohexylamine, mercaptobenzothiazole, and zinc contaminants were observed.
MISCELLANEOUS TECHNIQUES Gas chromatographic determination of formaldehyde in aqueous phase during the preparation of hydrocarbon-formaldehyde oligomers wcs described (77). An automated thermal desorption-gas chromatographic system was developed for gas chromatography of volatile components in polymers (78). Dynamic trapping of the thermally desorbed volatile organic components is followed by selective stripping of fractions onto a gas chromatographic column. Blends of rubbers containing NBR, CR, EPDM, NR, BR, and SBR were quantitated by pyrolysis-gas chromatography (79). Acrylonitrile in NBR and ethene, propene, and the third monomer in EPDM's were quantitated while CR could be identified in both sulfur-modified and sulfur-free CR. Analysis of pyrolysis products on a gas chromatographic system with a combination of flame ionization and flame photometric detectors allowed the identification of sulfur-containing compounds (80). Polyolefin rubbers were separated from the fiiers by boiling with xylene containing 2 M hydrochloric acid (81). Pyrolysis at 550 f 50 "C for 5 min followed by IR and pyrolysis at 600 "C for 1 min followed by gas chromatography were used for identification of the polymers. Analysis of bound rubber by pyrolysis-gas chromatography was used to study the distribution of carbon black in SBR-BR blends (82). The concentration of carbon black in a given rubber increased with increasing molecular weight. Dynamic head space-multidimensional gas chromatography-mass spectrometry were used in the study of volatiles in EPM (83). This combination of techniques resulted in better resolution and less overlapping of MS spectra and provided higher confidence in the results. Computerized quantitation of free sulfur in NR formulations was used to achieve better precision in HPLC (84). This method is claimed to be better than the standard ASTM titration procedure. The separation and identification of 22 antioxidants and light stabilizers by HPLC were described (85). The column used was Cla reverse phase with three different mobile phases: 100% acetonitrile, 90110 acetonitrile/water, and 80120 acetonitrile/water. The ratio of UV absorption at 254 and 280 nm was used for identification. Separation of extender oils, used in the rubber industry, into their characteristic groups was achieved by (a) dissolution in n-pentane to separate the insoluble asphaltines; (b) absorption of N-, S-, or 0-containing compounds on kaolin; (c) absorption of aromatics on silica; and (d) elution of the saturates in the eluate (86). This method was tested on a series of commercial extender oils, requires 5-6 h, and provides a precision of f0.10%. Dithiocarbamates were determined by HPLC after their conversion to cobalt(II1) complexes by reaction of the chloroform-acetone extract with cobalt(I1) chloride (87). Multiple peaks which were obtained in some cases were compared to the peaks obtained from cobalt complexes of known dithiocarbamates. Chromatographic separation of functionalized oligobutadienes required modification of the stationw phase and the functional groups (88). This was achieved by controlling the temperature and the interaction of the functional groups in the mobile phase. Quantitation of free sulfur in vulcanized rubber was achieved by scanning thin-layer chromatography of the acetone extract (89). Quantitation of carbon black in BR and in its blends with SBR and NR was obtained by metathesis degradation at 40 or 60 "C in the presence of WC16/Me4Sn and 1-octene (90).Sequence distribution and block structure of styrene in SBR and SIR were determined by GPC of the rubbers and their ozonolysis products (91). Styrene block sequences were 77-99% and a star styrene-butadiene-styrene was distinguished from a linear copolymer by comparison of the molecular weight and chemical composition of the main and shoulder peaks by GPC and also by comparison to the molecular weight of the block styrene sequence determined by ozonolysis/GPC. The sequence distribution of styrene units in vulcanized SBR was analyzed by high-resolution GPC of ozonolysis products obtained by ozonization of finely powdered samples suspended in dichloromethane, followed by reductive degradation with LiAlH4 (92). The fraction of monad, diad, and
triad styrene sequences, which were flanked by 1,4-butadiene units, and long styrene sequences leveled off at 100-150% of required ozone. The sequences in GPC fractions were determined by 'H NMR. Configurational sequences of styrene units and the arrangement of styrene and 1,2-butadiene units in SBR were characterized by 'H and 13CNMR analysis of the ozonolysis products separated by GPC and HPLC (93). The ozonolysis products from diad and triad styrene sequences flanked by 1,bbutadiene units showed two and three peaks in HPLC, respectively, reflecting the diad and triad tacticity. The ozonolysis products from styrene and 19-butadiene sequences were separated into three fractions by HPLC; the first and second fractions were assigned 1,4- and 1,2-styrene-1,4 structures differing only in tacticity, and the third fraction was a mixture of meso and racenic forms of 1,4-styrene-1,4 sequence structure. Combinations of these structures were studied in detail by HPLC. Weathering and aging characteristics of nonreinforced EPDM and fabric reinforced SBR roofing membranes were evaluated by TGA, DSC, and dynamic mechanical analysis (94). Identification and quantitation of NBRs and their blends with PVC were achieved by TG, DTG, and IR (95). Glass transition temperatures as determined by loss factor/ temperature curve increased with increasing acrylonitrile content. Microstructures of rubbers obtained from different plants and IR were studied by IR and NMR (96, 97). UV, 'H NMR, 13C NMR, SEC, and MS characteristics of phenylhydrazones derived from aldehydes and ketones chosen as models of conjugated carbonyl structures, which could result from oxidation of IR, were obtained (98). EPMs and their homopolymers were examined by GPC, 13C NMR, and DSC (99). Carbon-black-filled rubber compounds were analyzed by MS using direct thermal desorption with EI, CI, FI, and FAB-MS without liquid matrix (100). FI/FD was found to be most efficient for identifying typical organic additives in rubber stocks or their extracts. MS/MS was studied as a means of improved direct MS characterization of organic additives in rubber compounds (101). Daughter-ion, parent-ion, and neutral-loss scans were used to enhance the specificity of identification. Positron anhilation was reported to show a linear relationship with M y in methylvinyl silicone rubber (102). Wide-angle X-ray investigations were conducted on isotactic polypropene and its blends with EPM (103). The interpretation of scattering data to provide information on material structure was considered with reference to neutron scattering, small-angle X-ray scattering, and light scattering (104). Cross-link density of nonfilled peroxide-cured IR was determined with a medical X-ray computed tomography scanner which could detect variations of less than 2-3 m g / ~ m caused -~ by vulcanization (105). Phase behavior of blends of BR and SBR was studied bv light scattering (106). Carboxylated SBR latexes and oil emulsions were characterized by passing through filters of 12500 8, pore size to enable retention of filtrates of different particle size distributions (107). The wear surfaces of NR, BR, and NR-BR-SBR blends worn on a modified blade abrader were determined to be fractal (108). A method was proposed to determine the thermodynamic incompatibility of polymers, based on observation of the breakdown of the liquid cylinder of one polpner in the medium of another by the wave mechanism of destabilization (109).
The structure of IR and NR was studied by using molecular probes-sulfur and diphenylguanidine-by the diffusionsorption method in the range of 30-110 OC (110). Several high-temperature transitions were observed and their presence was confirmed by IR spectroscopy. The volatile matter content of raw NR was determined by using a microwave oven, which reduced the time required for this standard test (111). Quantitation of zinc sulfide was used to estimate the state of vulcanization of NR (112). ac polarography was used to determine copper and zinc in rubber (113). Cross-link structure of vulcanized rubber was determined by measuring the properties of the swollen rubber under uniaxial compression (114, 115). The method involved seANALYTICAL CHEMISTRY, VOL. 61, NO. 12, JUNE 15, 1989
lective breakdown of sulfide networks by standard reagents. Relative state-of-cure determinations by DSC, Mooney-Rivlin, and solvent swell methods were compared (116). A method was proposed for calculating the cross-link density based on equilibrium swelling data (117). The distribution of the degree of polymerization between cross-link sites was determined by subjecting the cross-linked NR to degradation under small strain, measurin the stress relaxation, and calculating the molecular weight fistribution between cross links (118). Swelling equilibrium experiments with benzene and cyclohexane on high cis IR were conducted to study cross-link density (I19). Extraction of small amounts of rubber samples was achieved by placing the samples in a porous PTFE bag with pores of 10-100 pm diameter (120). The degree of surface modification of rubber was determined by applying aqueous ethanol solutions with different surface tension and then observing their wetting behavior (121).
Defects in rubbers having blind holes and bonded with an adhesive were detected by holographic nondestructive testing (122). Traces of elementary sulfur were determined after cleaving the S8 ring with NaBH4 and precipitation of HgSz followed by measuring the excess of Hg(I1) ions by flameless AA (123). This method was adapted for determining free sulfur in rubber extracts. Moisture content of compounding ingredients was determined by measuring the heat of reaction with the Karl Fischer reagent (124).
ACKNOWLEDGMENT The permission of The Goodyear Tire & Rubber Company to prepare and publish this review is greatly appreciated. I specially thank Goodyear’s Technical Information Center, D. N. Thayer, and R. M. Goodrich for their invaluable help. The author acknowledges Chemical Abstracts Service for providing access to STN International to aid in the literature search used in the preparation of this work. LITERATURE CITED (1) Krishen, A. Anal. Chem. 1987, 52, 114R-119R. (2) Amer. Soc. for Testing and Materials 1987Annual Book of ASTM Sfandards; ASTM: Philadelphia, PA, 1967, 09,01, 359-361. (3) Frisone, Glno J. Encycl. folym. Scl. Eng. 1987, 8 , 1-6. (4) Bertrand, Guy Rubber World 1988, 193, 16-20. (5) Schnecko, H.; Angerer, G. Kaufsch. Gummi, Kunsfst. 1088, 4 7 , 149-53. (6) Nishi, Toshio Nippon Gomu Kyokaishl 1987, 6 0 , 659-66. (7) Sima, Alina; Nita. Elena; Moldovan. Zenovia Ind. Usoara 1987, 34, 349-5 1. (8) Veith, A. G. folym. Test 1987, 7 , 239-67. (9) Schuster, R. H. Kautsch. Gummi, Kunstst. 1087, 4 0 , 642-50. (10) Sircar, Anii K. Sagamore Army Mater. Res. Conf. R o c . 1987, 32, 73-115. (11) Heatley, F. Macromolecular Chemistry 1982, 2, 190-202. (12) Dorner, W. G. Kunst. flast. 1987, 3 4 , 10-2. (13) Dubois, Jacques Analysis 1988, 16, LXVI-LXXIII. (14) Mitchell, J., Ed. Munich, Carl Hanser Verkrg 1087, xvli, 573. (15) Cheng. H. N.; Bennett, Mark A. Makromol. Chem. 1987, 188, 2665-77. (16) Cheng. H. N.;Lee, G. H. J. folym. Sci., f a r t 8 : Polym. fhys. 1987, 25, 2355-70. (17) Chu, Chia Yeh; Watson, Kenneth Norman; Vukov, Rastko Rubber Chem. Technol. 1987, 6 0 , 636-46. (16) Van Der Velden, Geert; DMden, Cees; Verrmans, Ton; Beuien. Jo Macromolecules 1987, 20, 1252-6. (19) Curran, S. A.; Padwa, A. R. Macromolecules 1987, 20,625-30. (20) Clemmett, C. J.; Smith, E. G.; Harris, R. K.; Kenwright, A. M.: Packer, K. J. folym. Comm. 1907, 2 8 , 137-40. (21) Patterson, D. J.; Koenig, J. L. Appl. Spectrosc. 1087, 4 1 , 441-6. (22) Koenig, J. L.; Patterson, D. J. Elastomrlcs 1088, 118, 21-6. (23) Zaper, A. M.; Koenlg, J. L. Rubber Chem. Technol. 1987, 6 0 , 278-97. (24) Zaper, A. M.; Koenlg, J. L. Rubber Chem. Technol. 1987, 60. 252-77. (25) Bradbury, J. H.: Eiix. J. A.; Perrera, M. C. S.J. folym. Sci. 1088, 2 6 , 615-26. (26) Chang, C.; Komoroski, R. A. Polym. frepr. (Am. Chem. SOC. Div. folym. Chem.) 1988, 2 9 , 94-6. (27) Kuntz, I.;Powers, K. W.; Hsu, C. S.; Rose, K. D. Makromol. Chem.. Macromol. Symp. 1988, No 13/14,337-62. (26) Anachkov, M. P.; Rakovsky, S. K.; Shopov, D. M.; Razumovskii, S. D.; Kefely, A. A.; Zaikov, G. E. folym. Degradat. Stab//. 1988, 1 4 , 189-98. (29) Wharry, S.;Yeh, G. H. J. folym. Sci. Polym. Chem. 1986, 2 4 , 1065-7. (30) Jelinski, L. W. Developments in Block Copolymers-2 1985, 1-25. (31) Bauer, D. R. Frog. Org. Coatings 1988. 14, 45-65. (32) Tanake, H.; Sumi, Y.; Nishi. T. Reports in Progress in Polymer Physics in Japan 1984, 545-8. (33) Hatfield, 0. R.; Maciei, G. E. Macromolecules 1987, 20, 608-15.
ANALYTICAL CHEMISTRY, VOL. 61, NO. 12, JUNE 15, 1989
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(113) Sviridenko, V. G.; Lin, D. G.; Eiiseeva, I.M. Zh.Anal. Khim. 1987, 42, 1525-7. (1 14) Nakauchi, Hideo; Utsunomiya, Tadashi; Masuda. Kinji; Inoue, Sakae; Naito, Kazou Nippon Gomu Kyokaishi 1987, 6 0 , 267-72. (115) Nakauchi. Hideo; Kato, Shigo; Inoue. Sakae; Naito, Kazuo Nippon Gomu Kyokaishi 1987. 6 0 , 273-9. (1 16) Warley, R. L.; DeiVecchio, R. J. Rubber WorM 1987, 796, 30-2, 34-6, 38. (117) Pestov, S. S.; Shershnev, V. A.; Gabibullaev, I.D.; Soboiev, V. S. Kauch. Rezina 1988, 2 , 10-13. (118) Schoon, Douglas D. Int. S A M E Sympo . Exhib. 1988, 3 3 , 433-43. (1 19) Queslel, Jean Pierre; Fontaine, Frederic; Monnerie, Lucien Polymer 1988, 2 9 , 1086-90. (120) Tsujikaido, Isao; Matsuda, Yojiro Jpn Kokai Tokkyo Koho JP 62/ 194439 A2 (87/194439), 1987. (121) Rozenboim, N. A.; Ovchlnnikov, V. N.; Pestov, S . S . Kauch. Rezina 1987, 8, 27-8. (122) Luo, Jing Hua; Jlan, Ke Jian; Li Zhong Hua; Tan, Y Shan Proc. SPIEInt. SOC.Opt. Eng. 1987, 814, 449-54. (123) Puacz. Wojciech Acta Chim. Hung. 1987, 724, 293-8. (124) Soos, I.; Marik-Korda, P. Kautsch. Gummi. Kunstat. 1988, 4 7 , 572-4.
Surface Characterization J. E. Fulghum, G. E.McGuire,* I. H. Musselman, R. J. Nemanich, J. M. White, D. R. Chopra, a n d A. R. Chourasia Microelectronics Center of North Carolina, P.O. Box 12889, Research Triangle Park, North Carolina 27709
be decreased through postionization of the sputtered particles. There are currently three different methods being investigated for postionization. Sputtered neutral mass spectrometry (SNMS) uses electron impact ionization. Resonance laser ionization is used to selectively ionize a single element without interferences from other species; this technique is referred to by many names, including sputter-initiated resonance ionization spectroscopy (SIRIS) and surface analysis by resonance ionization of sputtered atoms (SARISA). Nonresonant ionization by laser photons, surface analysis by laser ionization (SALI), is also under development. Laser microprobe mass spectrometry (LAMMS) uses a laser as the primary beam for both sputtering and ionizing particles which are then massfiltered by a time-of-flight mass analyzer. Laser desorption/laser ionization methods use separate lasers for the desorption and ionization processes. Developments in mass spectrometry were discussed by Delgass and Cooks (A15). Mass spectrometric techniques have been compared by Balasanmugam et al. (A16),Grasserbauer (A17),and Ortner et al. (A18). Secondary ion and secondary neutral mass spectrometry in a quadrupole instrument were compared by Tuempner, Wilsch, and Benninghoven (A19). SIMS and acclerator-based mass spectrometries have also been compared (A20, A21).
INTRODUCTION Reviews of surface characterization have appeared in Analytical Chemistry every two years since 1977. (1-6) During this time the field has grown significantly in the volume of papers published as well as the number of applications and diversity of surface characterization tools. In the last two reviews ( 5 6 ) a table format was adopted to handle the large number of applications. With the ready availability of computer searches, this format does not provide the critical assessment of the literature that may be desirable. This review is being written by multiple authors with specialties in one or more of the broad categories of surface analysis in an attempt to highlight some of the more important advances in each of these areas. This review begins with literature from January 1987 and ends with literature from November 1988.
A. ION SPECTROSCOPY General Reviews
The application of ion spectroscopies in the analysis of materials was discussed by Briggs ( A I ) and Davies (A2);the use of nuclear microprobe techniques has been reviewed by McMillan (A3),Gossman and Feldman (A4),and Conlon (A5). The use of ion spectroscopies in the analysis of wave- uides (A6),thin films ( A n ,H in metals (At?),microelectronic tfevices (A9, AIO), fusion devices ( A l l ) ,biological specimens (A12), and polymers (A13) has also been reviewed. The accuracy of various surface analysis methods was evaluated by Powell (A14). There are several different ion spectroscopies involving mass analysis of secondary ions created by one of several different ionization methods. In secondary ion mass spectrometry (SIMS), a primary ion beam (normally of 1-10 keV) is used to bombard the sample surface. A small fraction of the sputtered secondary particles are ionized and can be mass filtered and detected. If the primary beam consists of neutral atoms, the technique is referred to as fast atom bombardment (FAB). Since only a small fraction of the sputtered material is ionized, the severe matrix effects observed in SIMS should 0003-2700/89/0361-243R$06.50/0
Secondary Ion Mass Spectrometry
Recent developments in SIMS were summarized by Katz and Newman (A22) and Adams and Moen (A23). Progress in SIMS imaging was discussed by Bernius and Morrison ( A B ) ,while static SIMS and FAB were evaluated by Fenselau and Cotter (A25) and Vickerman (A26). SIMS analysis of electronic materials has been discussed by Grasserbauer ( A 2 3 and Boudewijn and Janssen (A28). The use of SIMS in the analysis of thin layers in electronic materials has been reviewed by Galuska and Morrison (A29)and Vandervorst and Shepherd (A30). Several reviews of the metallurgical applications of SIMS have been written, including those of Degreve et al. (A31),Virag and Friedbacher (A32),and Gijbels (A33). The use of ion microscopy in marine research (A34) and organic 0
1989 American Chemical Society