Peter R. Griffiths Department of Chemistry Ohio University Athens, Ohio 45701
At a neriod when each month seems r o herald the cmnmercial intrt,duction o f a new analvtical insfrumenr, the continuing utility of established instrumental techniques sometimes gets forgotten. The case of infrared (IR) spectroscopy may be regarded as typical. While even the editor of this journal has suggested that IR spectroscopy is becoming obsolescent ( I ), most industrial laboratories involved with organic compounds continue to use IR as an important tool for qualitative and quantitative analysis. The market for IR spectrophotometers is still in.. . . creasing, and it nas been rorecast m a t
i t will continue to increase over the next decade both i n Amerira and Fu-
$5000, aiid even the highest performanre d "+i:., m ~ w"...."+-n..l.-+...,."+m-" rarely cost more than 330,000. In addition, a wide variety of sampling accessories for spectrophotometers are commercially available to further increase the versatility of the technique. "~'~"V~,."'".,.'LL.-
rope.
The reasons for the popularity of IR as an analytical technique have been thoroughly expounded for the last 20 years. Samples of all types can be analyzed both qualitatively and, to a slightly lesser extent, quantitatively. Sample preparation is usually simple, although some expertise is needed for the measurement of the spectrum of samples weighing less than one-tenth of a milligram. Small IR spectrophotometers can be purchased^. from.many manufacturers a t a cost or less tnan
Figure 1. Pye-Unicam (Ynrk St., Cambridge CB1 2PX, England) Model SP-1000 Excellent low-cost instrument with Spectral range of 3800-625 cm-'. Note simplicity 01 controis on spectrometer, ailowing nonspectroscopist to measure infrared Spectra with minimum Of diffiwity
.
Instrumentation In spite of inflation, the price of small grating spectrometers has not changed dramatically over the last decade, and new instruments are still introduced a t frequent intervals, often with features which allow relatively unskilled technicians to obtain good quality spectra routinely, provided that they can prepare decent samples (Figure 1). Medium-priced grating spectrometers (around $10,000) now have the performance which was associated with far more expensive equipment, say 10 years ago, and may be considered to he one of the "bargains" on the instrumental scene (Figure 2). The field of high-priced (>$25,000) IR spectrophotometers has seen several important innovations in the past few years. For example, the use of two choppers and a digital ratio-recording method has enabled the Perkin-Elmer Model 180 grating spectrophotometer (Figure 3) to realize substantial improvements in sensitivity over singlechopper, optical-null type instruments, especially for the measurement of samples of low transmittance. However, in recent years the most spectacular instrumental advances have come from the development of interferometric techniques, especially Fourier transform spectroscopy (FTS) (Figure 4). A t one time i t appeared that Hadamard transform spectroscopy (HTS) might present a viable alternative to FTS, but in the last year H T S seems to have disappeared from the instrumental scene (2).This au-
Figure 2. Beckman (Scientific Inst. Div., Fullerton. Calif. 92634) Model 4250 grating spectrophotometer Typical of mediumIpriced instruments which possess several features n e c e ~ ~ a for r y measuring spectra of wide variety of samples. Among these features are wide spectral range (4000-200 cm-'), ordinate and abscissa scale expansion, and meter which enables amplifier gain to be set correctly under ail measurement conditions
Report
thor recently summarized the latest developments in interferometric instrumentation (31, and even in the short time since the publication of that article, several new Fourier trans. form spectrometers have been introduced commercially. One of the principal reasons for the popularity of Fourier transform spectrometers is the versatility of the data systems which are integral components of these spectrometers. Small data systems are now also becoming available for grating spectrometers which will give the users of these instruments (and in uarticular the users of spectruinetek which have been designed with a digirnl interiace in mind1 many d t h e ad\,antages of the Fourier rransfurin sprctromerer. Anulher major advance in recent years is seen in thr development of inrrared analyzers for the qiiantitative di,terminaticm of known substances. These instruments full into two cafegories: single-purpose analy7ers which mvasure a sprrified narruu' hand of radiation detined hy an uptical filter and thc: more sophisticated insrruinents u,hich may he tuned over a r a n g e d frequencies. The latter instruments arc more versatile than the single-frequenry annly~ers.but they may also be slightly less acrurate since it is possililc toset the center ofthe optical pass-hand for a given analysis at slightly different frequencies on difierrnt days. inirarcd analyzers are used ruutineb for wx.eSs ControL fur example. in derermining the concentratiun of reartants and prodirrt; during methanol synthesis. rncthoire rrarking, .and acetylene manufacture. 'l'hi,y are beroming widels applied IO monituring potrntially toxic gases in ambient air, and the rlctrrminations of cnrhon monoxide and vinyl chloride ( 4 I in the
atmosphere are both being performed continuously with filter analyzers (Figure 5). Another important area where these instruments are being used is the measurement of carbon dioxide in a wide variety of media, such as in expired air in experiments with small animals and the atmosphere around perishable foodstuffs (infrared Industries Inc., P.O. Box 989, Santa Barbara, Calif. 93102). For the most accurate work, accessories for these instruments have been devised by which deviations from Beer's Law may be corrected and readings mav be nrovided directlv in units of
concentration. Continuous recorders are also available for many of these analyzers, so that, for example, levels of potentially toxic gases may he monitored around the clock a t several sites around a plant, and audible alarms can be installed to signal if the concentration exceeds a predetermined limit.
Accessories Earlier in this paper, the capability of IR spectroscopy to characterize samples of many different types was mentioned. This versatility is derived from the fact that not onlv can Dure
Figure 3. Perkin-Elmer (Inst. Div.. Main Ave., Norwalk. Conn. 06852) Model 180 grating spectrophotometer Probao hlgheel performance commercially a~~~g m "Q Speciropholomeler F computer cornpal o I/. far infrared extension IO 33 cm ana digilal ~BIIO-~OCUIOng
-'
~ lnciuda~ easy ~
Figure 4. Digilao (237 Putnam Ave.. Cambridge, Mass. 02139) Model FTS15 Fourier transform spectrophotorneter Advanlages over gral ng spenromelers include ncreasao scan speed (comp ele rpeclrum m less than 1 sec , logelhcr v th h gn s gnal-la-nose ratio ana nign reso n on 0. 1-0" m n comp-ler a m d sc memory g b e operalor greal uersalhly n stnrng EpeClla am man pJlat "9 daw awe, measurement
A h A - Y T C A - C A E M I S T R Y . VOL. 46, NO
14. DECEMBER 1974
1207A
~
~
Figure 5. Wilks Scientific (Box 449, S. Norwalk, Conn. 06856)
Miran-I portable gas analyzer Twentymeter folded-path gas cell incorporated in instrument permits rapid quantitative analysis of trace gases in atmosphere
samples in 1- or 2-mg quantities he readily studied by standard infrared sampling techniques (e.g., capillary or cast films, KBr discs, Nujol or Fluoroluhe mulls, solutions, or in the gas phase), hut also less routine samples may he characterized by the use of sucn sampling amacnmenm as specular reflectance accessories for the study of surface species; attenuated total reflectance (ATR) devices for studying intractable samples such as paper, coatings, fihers, and cloth; beam condensers for microsamples such as micro-KBr pellets and micro ter volume solutions; and long path gas cells for measuring trace (ppm and pph) gases in the atmosphere. 1.
1 1
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Reference Data
The tremendously wide variety of problems that can he solved by IR continues to make the infrared spectrouhotometer a vital instrument in a large number of analytical lahoratories. So diverse are the problems which have been solved by IR that it has become a rather time-consuming task for the new spectroscopist to readily locate the many descriptions of IR applications and techniques which are available from one source or another: in fact, in this era of the information explosion, it is often difficult even for experienced spectroscopists to follow all the latest work which has been published nationally and internationally. In an attempt to disseminate this wealth of useful information to all IR spectroscopists, an extensive bibliography of IR literature has been prepared by the Cohlentz Society (971 Main Ave., Norwalk, Conn. 06851) which will he available to its membership in the very near future. Large collections of reference spectra of pure compounds have also been published over a period of many years by such sources as Sadtler Research Laboratories (3316 Spring Garden St., Philadelphia, Pa. 19104), the Coblentz Society, Documentation of Molecular Spectra (Butterworths, London, England), and the Thermodynamics Re1208A
*
search Center (Texas A&M Univ., College Station, Tex. 77843). Besides publishing the spectra of pure compounds, Sadtler has also put out extensive compilations of the spectra of commercial formulations under such categories as pesticides, polymers, surc-"L"..*" ^L..^^-lA. ~ -*- ~*~l.".Lu. ,n r u y I L I L L ~ L I ~ , ~ U U I C ULUW, r aiding the industrial analytical chemist to readily identify a wide variety of compounds from many different >""ICC>.
Spectral Search
compurerizeu spec~rarsearcn rouuneb (Figure 6 ) ;to use this service, the chemist must note the frequencies of the major bands in the spectrum of an unknown material and send these data (together with any further chemical information such as elements known to he present or absent in the compound which he is trying to identify) via a teletype terminal to a large remote computer. The search is made through a very large data base; over 100,000 spectra have been coded by ASTM and are used in most data hanks. With some search systems, answers can he received by a matter of seconds after the original data were transmitted through the telephone lines. The answer is usually given in the form of a list of the 20 most prohahle spectral matches, together with a numerical estimate of the probability that the unknown spectrum matches the known, coded spectrum. In view of the variety of spectrometers and sampling methods that have been used to measure the spectra for the data base, a surprisingly high percentage of correct matches is found using these searching systems. FACSS The recent meeting of the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) in Atlantic City, N.J., serves as a good illustration of the continuing importance of IR as an analytical technique Of the 13 principal symposia a t this
A N A L Y T I C A L CHEMISTRY, VOL. 46. NO. 14, DECEMBER 1974
meeting, three were completely devoted to IR ("Infrared Spectroscopy-the Great Detective," "Moving Infrared from 'Lab' to 'Line','' and "Applications of Fourier Transform Spectroscopy"), while several papers in other sessions also covered IR applications. ,..-A
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gram should certainly reassure the doubtful that IR is alive, not merely as a routine laboratory instrument, hut also as an important research technique. The topics covered in the symposium entitled "Infrared Spectroscopythe Great Detective" nicely illustrate the types of industrial problems which have been studied in recent years by vibrational spectroscopy. They ranged from descriptions of how IR spectroscopy is used forensically, both in a police crime laboratory and in the identification of the source of oil spills, to topics in areas of applied research, such as the study of surfaces and textiles. Oil Spills The work of Chris Brown's group a t the University of Rhode Island on the identification of oil spills is an excellent example of how the qualitative and quantitative nature of IR can he applied simultaneously for industrial problem solving (5).Petroleum is, of course, composed primarily of a complex mixture of hydrocarbons, and it might therefore he expected that the infrared spectra of all petroleum products would he quite similar. This is certainly true above 1300 cm-l, hut between 1200 and 650 em-', there is a "fingerprint" region which has been used to obtain an unambiguous assignment of each petroleum product. The spectra of over 300 petroleum products have been measured, and each spectrum shows significant differences in the low-frequency region. By storing the absorptivities of 21 hands in thi3 region in a computer data hank, the spectrum of any unknown petroleum sample can he matched with a spectrum of known or-
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Remote Temperature Monitoring- built-in. Full scale display of any lo", 50°, or loo'%, with thermistor placed either in sample or holder. Adjustable cycle/dwell time-no extra cost. Digital timers control cycle of 0-99 seconds or 0-99 minutes. Dwell 0-99 seconds. Additional features-same low price. Digital wavelength scanning and display, computer compatibility, digital display of absorbance to 3.000 Abs, boxcar type integration. Research quality-low cost. Accuracy to 10.001 Abs, resolution of 0.1 nm, and stray light of less than 0.1% at 220 nm. For fastest return of complete specifications and ordering data, write directly to GCA/McPherson Instrument, 530 Main St., Acton, MA 01720. Or see our local regional manager in your area. Need immediate information? Call Howard Schwartz at (617) 263-7733. 'North American price
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EARS IN CHEMICAL) AMOCO 533 ANTIOXIDANT (2,6-DCt~rt-BUTYl-p-CR€SOL) 2,6-Di-tert-BUTYL-p-CRESOL 2,dDl-tert-BUTY L-p-CRESOL
2,6-Di-tert-BUTYt-p-CRESOL
CATALIN ANTIOXIDANT CAO-1 (2,6-Dl-TERT-BU~L-p-CRESOL)
16
895
SP0134
+ + + +
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Figure 6. Output from Sadtler's IRIS spectral search program Wavelengths of major and minor bands in petrochemical spectrum were entered, and an excellent match was given by several different coded spectra of 2,6di-tert- butyl-p-cresol
igin. Even quite weathered samples have been identified in this fashion, and the sources of every spill investigated by Brown's group have been successfully assigned. Forensic Science Infrared spectroscopy has also been used in police forensic laboratories as a versatile tool for a variety of problems. Although the sensitivity of most infrared spectrophotometers is not sufficiently high to allow drugs to be 1210 A
rapidly identified by using blood or urine samples from overdose patients, IR does provide a rapid means of identifying the active ingredient of the pill or capsule that might have caused this overdose. Sadtler Research Laboratories has published a collection of the spectra of commonly abused drugs, for which the samples were prepared by extracting prescription drug formulations with alkaline and acidic chloroform; this technique usually leaves the great majority of all fillers and binders
A N A L Y T I C A L C H E M I S T R Y , V O L . 46, N O . 14, DECEMBER 1974
unextracted. After simply casting a film of each extract onto a KBr plate, the active ingredient of a pill may be identified just minutes after the pill was first discovered. In another method for the identification of drugs, Hannah and Pattacini (6) have described a simple method by which the spectrum of a pure drug may be analyzed to determine the category under which the drug may be classified (Figure 7 ) . In most cases, only a few compounds fall into each
@
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1211A
Figure 7. Flow diagram for routine drug identification using infrared spectra By checking presence or absence of bands in certain spectral regions, compound can be classified under one of 10 groups (A-J). For example, Group C contains all barbiturates, while all drugs in Group H are amphetamines. (Repro. duced from ref. 6)
category so that a rapid comparison with two or three reference spectra usually leads to an unambiguous identification. Of course, drugs are not the only types of compounds encountered in a typical forensic laboratory, and the New York State Police Forensic Laboratory has an operational data file retrieval system containing the full ASTM data base and other coded spectra, which has been used in the solution of several criminal cases ( 7 ) . In forensic studies of a different type, IR spectroscopy has been used for identifying certain pigments in ancient paintings and distinguishing these from forgeries. Whereas inorganic pigments can be readily recognized by X-ray diffraction or optical emission spectroscopy, organic pigments cannot; for these materials infrared spectroscopy provides a sensitive alternative technique which has been applied successfully several times in the past (8).The identification of paint samples has also proved to be important in police forensic laboratories; for example, paint chips from automobiles involved in accidents have been characterized by using a micro-ATR accessory (9 ). ATR spectroscopy is particularly useful for identifying black paints containing carbon black, since the measured spectrum depends essentially on the paint base. Another sampling technique for pigments involves taking a suspension of the paint in a suitable solvent, such as petroleum ether, and filtering the suspension through a MilliporeR filter. After drying, the filter is placed on an ATR plate, and the spectrum of the pigment is measured ( 1 0 ) .Particulate toners and extenders in writing inks, and even colloidal particles in beer and tea, have also been identified by using a similar sampling technique. Surface Chemistry and Catalysis
Surface chemistry and catalysis are two related areas of applied research 1212A
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in which IR has played an important role. Since the earliest work of Terenin in Russia and Eischens in America, many industrial laboratories have used IR as a probe to identify adsorbed molecules, to determine differences in adsorption sites, and to study the reactivity of surfaces. Recently, catalytic silica surfaces have been modified by reaction with active organic molecules such as organosilanes; IR has been most helpful in following these reactions and checking the stability of the reaction products. In other work, described a t the FACSS meeting by Charles Angel1 of Union Carbide Research Laboratories (11 ), the reaction of alcohols with free silano1 groups on silica surfaces has been followed by IR, and the manner in which the reaction is enhanced by the presence of Lewis bases was also studied. In studies with other types of catalytic materials, finely powdered metals have been dispersed in silica and alumina, thereby providing a large surface area on which gases can be adsorbed. By pressing the dispersion into a thin pellet, IR bands due to gases adsorbed on the metal surface can be measured, and information on the nature of the bond between the adsorbed molecule and the metal can be derived (12, 13).Recently, work has been described where the spectra of monomolecular layers of molecules adsorbed on single crystals of metals have been measured a t different orientations of the crystal faces ( 1 4 ) ;in this way a more fundamental idea of the processes involved in catalysis has been obtained. Polymers In the area of macromolecular chemistry, infrared spectroscopy is one of the most commonly used techniques for the qualitative and quantitative analysis of polymeric materials. Because of the different physical properties of polymers, several differ-
ANALYTICAL CHEMISTRY, VOL. 4 6 , NO. 14, DECEMBER 1974
ent sampling techniques must be used in the study of polymer spectra (15). These include the preparation of KBr pellets, cast films (where a solution of the polymer is dropped onto a salt window after which the solvent is evaporated, leaving a film of the polymer), and hot press films (where a chip of the polymer is placed between two salt plates on a hot plate which is heated to the point a t which the polymer softens); ATR and pyrolysis techniques have also been applied to the analysis of polymers. To aid in the rapid identification of polymers, flow charts have been developed (16) similar to the one shown earlier for the identification of drugs from their infrared spectra. Besides the simple identification of polymers, infrared spectroscopy can be used to determine their stereochemistry, the types of additives, the degree of degradation by weathering, the presence of a copolymer, and the chain length, orientation, and crystallinity of a polymer. For example, in the spectrum of poly-(isobutylene) shown in Figure 8 (A), the doublet a t 1390 and 1365 cm-l has been assigned to the t -butyl end-groups. By determining the relative intensity of these bands and the band centered a t 1470 cm-', the chain length of the polymer may be estimated. Similarly, in the low-frequency region of the spectrum of poly-(propylene) shown in Figure 8 (B), the weak band a t 460 cm-l and the very weak band a t 540 cm-I are due to crystalline isotactic poly-(propylene). Many of the types of analysis listed above are suitable for automation, and Edward Brame of Du Pont recently described how his group automated a commercial infrared spectrophotometer for polymer analysis ( 1 7 ) . Additives in polymers can also be identified by IR. One method which has been used for this purpose is to dissolve the polymer in a suitable solvent and separate the additives by column chromatography. Pyrolysis tech-
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ANALYTICAL CHEMISTRY, VOL. 46, NO. 14, DECEMBER 1974
1213A
Figure 8. (A) Spectrum of smear of oolyisobutylene on KBr. (E) Spt?drum of hot press film of polypropylene on KBr. (Reproduced from ref. 75)
mode a t 22 40 cm-I. Aft er calibration niques will often yield a distillate curves hav e been set up by measuring which is highly characteristic of the the spectrr1 of MMA-AI V copolymers parent polymer, while the pyr,olysis of of known composition, ?xtremely acelastomers such as rubbers anId adhecurate dettsrminations oNf the copolysives has allowed the identification of mer can be rapidly perfiormed. stabilizers, antioxidants, and acceleraA severe analytical pi.ohlem contor materials as well as the pa rent cerning a ntewly developled food packelastomer. t l v rle-rriherl aging .mate. rial was recein_"_, Although the photometric 2iccuracy I.l X J., In which the extremely small .~~~...~. ~~.~~ of infrared spectrophotometers has (10-50 ppb) amoun t of poly,mer disseldom been regarded in the past as solved from a nitrili?rubber modified being high enough to piErmit quantitaacrylonitrile-meth) 71 acrylate polymer tive analysis to be perf1irmed to an achad to be quantitatively determined curacy greater than fl'%,they are now to satisfy FDA requiirement!3. The being used in some indiustrial lahoraminute residue rem aining af t e r the tories to obtain results a t somewhat Ierving ...~ solvent had been ev aporaterI .-higher accuracy than ttlis. One examthe soluble fraction of the polymer ple of such a determinaItion is the was redissolved andIevaporated on analysis of the relative quantities of KBr. Analysis for the low levels of the monomer units of a poly-(methyl polymer in the micropellet still remethacrylate-acrylonitrile), MMAauired 10X ordinate scale expansion A?, copolymer. The use of solutions i n the grating spectrophotometer always allows the most accurate rt used for this measurement. sults to be obtained by infrared SI:,ectroscopy, since samples of known conell of Automotive Industry centration can be contained in a c In the same issue of ANALYTICAL known path length. MMA-AN re;idily CHEMISTRYin which the previous dedissolves in dimethyl sulfoxide, t hle termination was described, Lynn spectrum of which is essentially fi'ee of Lewis of General Motors Research absorption hands between 1650 aiid Laboratories described several appli2400 cm-1. The amount of methyll cations in which IR sDectroscouv methncrylare i n (lt*rcrminedby IISIine ._is used in the automotiie industry (19). rhv cnrhunyl >rrert hing mode a1 I IC0 For example, in the area of product cm .:, and rhr a( rylonifrile is rlrterassurance, IR spectra of shipments of mined by using the ni1ri.e stretrh ing
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. 1
1214A
AhA-YT CAL CdEMlSTR Y . VOL 46. NO 14. DECEMBER 1974
enaine oil are routinely measured to detect possible deviations in the base oil and additive content. In a less routine analysis, the amount of synthetic rubber (stvrenehutadiene couolvmer) in dustfalland aerosol samples collected near a highway was determined. Gross organic materials were first extrSrtnA frnm ".-l""-...tho ".."crmnln .uith ..."..hnnmno ll.._.._, " after which the tire ruhher was suluhilized with 0-dichlorobenzene in the presence of oxygen and cast as a film for measurement by IR spectroscopy.
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been described above.were made with grating spectrophotometers, but recently Jack Koenig of Case Western Reserve University has described some very elegant applications of Fourier transform spectroscopy in macromolecular research (20-22). He has obtained interesting new data on subjects such as the drawing of polyethylene, the fracture of polystyrene, radiation cross-linking of polymers, and carbon-filled rubbers (Figure 9). For example, be has been able to study changes in certain infrared ahsorption bands caused when carbon black is added to rubber and when plasticizers are added to PVC (Figure 10).
Now. ..scan to 400 cm-i with a low-cost IR spectrophotometer. More information from every sample. The 735 is the first low-cost instrument to scan from 4000 to 400 cm-1 and provide extra qualitative information about every sample. Use of a new type of diffraction grating, the dual-blaze grating, allows the full range to be covered without the expense and inconvenience of grating changes. The additional range makes characterization of closely related compounds easier; isomers can be differentiated and many inorganic and organohalogens identified. loo
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Auto-Chek gain simplifies a critical step. The Model 735 is designed to be operated with equal ease by both the specialized and inexperienced user. Newcomers to infrared are often baffled by the task of setting the instrument gain but now Auto-Chek has solved the problem. Just push the button and if the gain is set correctly the pen will deflect exactly 10 divisions. If not, turn the control until it does, You don't even have to remove your sample: what could be simpler than that? To further assure recording precision, the flat-bed recorder is directly coupled to the monochromator drive and is simple inboth concept and oDeration.
Low running costs. The full range of the instrument is covered by KBr accessories, with only fractional increase in cost and no changes in sampling methodology. Charts cost only 5 cents apiece and you can even use standard graph paper for scratch runs,
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For more information.. If you would like to take a closer look at the Model 735, request our full-color brochure or arrange to evaluate the instrument itself. Write to the Instrument Division, Perkin-Elmer Corporation, Main Avenue, Norwalk, Connecticut 06856.
Model 735 Infrared Spectrophotometer
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ANALYTICAL CHEMISTRY, VOL
46, NO 14, DECEMBER 1974
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(11) C. L. Angell, paper presented at 1st FACSS Meeting, Atlantic City, N.J.,
No". 1974. (12) L. H. Little. "InfraredSpeetra of Ad." Press, Lonsorbed S ~ e e ~ e sAcademic don, Enilland, 1966. (13) M. L. Hair, "Infrared Spectroscopy in
Fiaure 9. ComDarison of sDectrum of carbon-filled rubber samDle (A) as measured msform spectrophobigrating spectrophotometer and (B) as measured by Fourier iransform er Ltd.) tometer (reproduced from ref. 22; copyright 1974, McLean-Hunter
Figure 10. Infrared spectrum in carbonto-carbon double-bond stretching region for (A) carbon-filled and (B) unfilled polvbutadiene (Reproduced from ref. 22; copyright 1974, McLean-Hunter Ltd.)
I T m l n n m m t . in in in. techniques. New developments infrared instrumentation are still verv evident. The inexpensive IR analyzer can he used for the quantitative analysis of a variety of samples, for ambient air monitoring, and for process control. For the laboratory, small grating spectrometers are being made more sensitive with little increase in price. However, in the (admittedly biased) opinion of this author, the major advance of the past year has been seen in the development of Fourier transform spectrometers designed with the industrial analytical chemist in mind. Extremely versatile instruments with a price tag around $40,000 were shown at the recent FACSS meeting, while an even cheaper special-purpose interferometric spectrometer for the online analysis of nanogram quantities of compounds eluting from a gas chromatograph (Spectrotherm Corp., 3040 Olcott St., Santa Clara, Calif. 95051) was also introduced for the first time at this meeting. Infrared spectroscopy is certainly not entering a period of senescence, nor is it merely maintaining its reputation as an analytical workhorse; rather, it is becoming one of the more exciting areas of analytical research.
References (IH. )A. Laitinen,Anal. Chem., 45,2305 119721 l_l._,.
(2) T. Hirschfeld and G. Wijntjes, Appl. Opt., 12,2876 (1973). (3) P. R. Griffiths, A n d Chem., 46,645A
(1974).
Future of Infrared
(4) R. L. Hudson, paper presented at 1st
At this point, it would he possible to enumerate many further applications of IR spectroscopy, industry by industry. Suffice it to say at this point that in spite of the editorial views expressed in this JOURNAL, infrared spectroscopy is very much alive in the industrial analytical laboratory and shows every evidence of holding its own against competitive instrumental
(5) C. W. Brown, ibid. (6) R. W. Hannah and S. C. Pattacini, "The Identification of Drugs from Their Infrared Spectra," Perkin-Elmer Applications Study No.11,1972. (7) R. H. Ellis, paper presented at 1st FACSS Meeting, Atlantic City, N.J., Nav. 1974. (8) J. S. O h , M. E. Salmon, and C. H. O h , Appl. Opt., 8,29 (1969). (9) H. J. Walls, ibid., p 21.
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Surface Chemistry," Marcel Dekker, New York, N.Y., 1967. (14) 3. Pritchard and M. L. Sims, Trans. Faraday Soc., 66,427 (1970). (15) M. V. Zeller and S. C. Pattacini, "The Infrared Grating Spectra of Polymers," Perkin-Elmer ADDlications Studv No. .. 13,1973. (16) R. E. Kagarise and L. A. Weinberger, "Infrared Spectra of Plastics and Resins," Naval Research Lab, Rept. 4369, Washington, D.C., 1954. ( (17) E. C. Brame, paper presented at 1st FACSS Meeting, Atlantic City, N.J., No". 1974. (18) V. F . Gaylor, Anal. Chem., 46, 897A ( (1974). (19) L. L. Lewis, ibid., p 867A. (20) J. L. Koenig, Amer. Lab., 9 (Sept. 1974). (21) J. L. Koenig, paper presented at 1st FACSS Meeting, Atlantic City, N.J., No". 1974. (22) J. L. Koenig and D. L. Tahb, Can. Res. Deuelop., 7.25 (1974).
P e t e r R. Griffiths i s a n assistant professor of analytical chemistry at Ohio University a t Athens, Ohio. He ohtained his doctorate at Oxhrd University and then spent two years working with Ellis Lippincott's group a t the University of Maryland. Following this, he worked as product specialist for Fourier transform spectroscopy with Digilah Inc., Cambridge, Mass., and then as manager of the Analytical Services Laboratory at Sadtler Research Laboratories, Inc., in Philadelphia, His current interests include the quantitative remote analysis of gases by infrared emission spectroscopy and the study of chromatographically separated fractions by FTS.
