Peter R. Griffiths Department of Chemistry Ohio University Athens, Ohio 4 5 7 0 1
Industrial Problem Solving At a period when each month seems to herald the commercial introduction of a new analytical instrument, 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 (1 ), 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 increasing, and it has been forecast that
it will continue to increase over the next decade both in America and Europe. 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 at a cost of less than
Figure 1. Pye-Unicam (York St., Cambridge CB1 2PX, England) Model SP-1000 Excellent low-cost instrument with spectral range of 3800-625 c m - 1 . Note simplicity of controls on spectrometer, allowing nonspectroscopist to measure infrared spectra with minimum of difficulty
$5000, and even the highest performance grating spectrophotometers rarely cost more than $30,000. In addition, a wide variety of sampling accessories for spectrophotometers are commercially available to further increase the versatility of the technique. 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 at 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 be 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). At one time it appeared that Hadamard transform spectroscopy (HTS) might present a viable alternative to FTS, but in the last year HTS 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 medium-priced instruments which possess several features necessary for measuring spectra of wide variety of samples. Among these features are wide spectral range (4000-200 c m - 1 ) , ordinate and abscissa scale expansion, and meter which enables amplifier gain to be set correctly under all measurement conditions 1206 A ·
ANALYTICAL CHEMISTRY,
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1974
Report
bγ lnfrared Spectroscopy thor recently summarized the latest developments in interferometric in strumentation (3), and even in the short time since the publication of that article, several new Fourier trans form spectrometers have been intro duced commercially. One of the prin cipal reasons for the popularity of Fourier transform spectrometers is the versatility of the data systems which are integral components of these spectrometers. Small data sys tems are now also becoming available for grating spectrometers which will give the users of these instruments (and in particular the users of spec trometers which have been designed with a digital interface in mind) many of the advantages of the Fourier trans form spectrometer. Another major advance in recent years is seen in the development of in frared analyzers for the quantitative determination of known substances. These instruments fall into two cate gories: single-purpose analyzers which measure a specified narrow band of radiation defined by an optical filter and the more sophisticated instru ments which may be tuned over a range of frequencies. The latter in struments are more versatile than the single-frequency analyzers, but they may also be slightly less accurate since it is possible to set the center of the optical pass-band for a given analysis at slightly different frequencies on dif ferent days. Infrared analyzers are used routine ly for process control, for example, in determining the concentration of reactants and products during methanol synthesis, methane cracking, and acet ylene manufacture. They are becom ing widely applied to monitoring po tentially toxic gases in ambient air, and the determinations of carbon monoxide and vinyl chloride {4 ) 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 atmo sphere 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 de vised by which deviations from Beer's Law may be corrected and readings may be provided directly in units of
concentration. Continuous recorders are also available for many of these analyzers, so that, for example, levels of potentially toxic gases may be mon itored around the clock at several sites around a plant, and audible alarms can be installed to signal if the con centration 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 only can pure
Figure 3. Perkin-Elmer (Inst. Div., Main A v e . , Norwalk, C o n n . 0 6 8 5 2 ) Model 180 grating s p e c t r o p h o t o m e t e r Probably highest performance commercially available grating spectrophotometer. Features include easy computer compatibility, far infrared extension to 33 c m - ' , and digital ratio-recording
Figure 4. Digilab ( 2 3 7 Putnam A v e . , Cambridge, Mass. 0 2 1 3 9 ) Model FTS15 Fourier t r a n s f o r m s p e c t r o p h o t o m e ter Advantages over grating spectrometers include increased scan speed (complete spectrum in less than 1 sec), together with high signal-to-noise ratio and high resolution. Built-in minicomputer and disc memory give operator great versatility in storing spectra and manipulating data after mea surement
ANALYTICAL
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Figure 5. Wilks Scientific (Box 4 4 9 , S. Norwalk, Conn. 06856) Miran-I portable gas analyzer Twenty-meter folded-path gas cell incorporated in instrument permits rapid quantitative analysis of trace gases in atmosphere
samples in 1- or 2-mg quantities be readily studied by standard infrared sampling techniques (e.g., capillary or cast films, KBr discs, Nujol or Fluorolube mulls, solutions, or in the gas phase), but also less routine samples may be characterized by the use of such sampling attachments as specular reflectance accessories for the study of surface species; attenuated total reflectance (ATR) devices for studying intractable samples such as paper, coatings, fibers, and cloth; beam condensers for microsarhples such as micro-KBr pellets and microliter volume solutions; and long path gas cells for measuring trace (ppm and ppb) gases in the atmosphere. Reference Data
The tremendously wide variety of problems that can be solved by IR continues to make the infrared spectrophotometer a vital instrument in a large number of analytical laboratories. 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 Coblentz Society (971 Main Ave., Norwalk, Conn. 06851) which will be 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 Re-
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, surfactants, abused drugs, etc., thereby aiding the industrial analytical chemist to readily identify a wide variety of compounds from many different sources. Spectral Search
Another aid in this area is found in computerized spectral search routines (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 be 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 banks. With some search systems, answers can be 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 probable 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 at this
1208 A · ANALYTICAL 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. Just a quick glance at the FACSS program should certainly reassure the doubtful that IR is alive, not merely as a routine laboratory instrument, but also as an important research technique. The topics covered in the symposium entitled "Infrared Spectroscopy— the 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 at 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 be applied simultaneously for industrial problem solving (5 ). Petroleum is, of course, composed primarily of a complex mixture of hydrocarbons, and it might therefore be expected that the infrared spectra of all petroleum products would be quite similar. This is certainly true above 1300 cm - 1 , but between 1200 and 650 cm - 1 , 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 bands in this region in a computer data bank, the spectrum of any unknown petroleum sample can be matched with a spectrum of known or-
UCC EB 11/04/70 13:59 CH 1-02 USER ID*ABC,IRIS IRIS V-3F ARE Y0U fAMIUAR WITH IRIS|Y 0R N? |:Y WHICH INTERVIEW? :3 SAMPLE V 1 : ACC0UNT NUMBER? -.999 PASSWORD? ; XYZ TITLE F0R PR0BLEM?; I0N01 ? MAJ0R PEAKS?:6.8,7,Û,7.2,7.4,7:.6,8.0,8.1,8.3,8.9,11.5,/ MAJ0R PEAKS?:12.9 M1N0R PEAKS?:6.2,7.9,9.7,10.7,11.2, H0 PEAK AR£AS? : 5.5-6.i,6.3-6.7,9.8-10.5,l 1.6-12.8,13.1-15.0, CHEMISTRY PRESENT?· CHEMISTRY ABSENT?: WIGGLE?:! • ' ; • - . PRE-C0NCEIVED P0SSIBILITIES?: FILES T0 SEARCH[Y/Nj: SRL STD?:¥ SRL C0M?:Y 0THÊRS?: READY T0 CARRY 0UT SEARCH[Y 0R N?]:Y RESULTS WILL BE IN FILE E00380 C0 00 Y0U WISH T0 WAIT F0R RESULTS(Y 0R N? |=Y REVIEW V-3C UCC-SRL IRIS V-2 REP0RT F0R I0N0L ? SEARCH # 1 FILES SEARCHED SC0M SSTD SPECTRA STRATEGY MIN WT CHEMISTRY WIGGLE 7 2 #1 + 2 #1A #1 1 # 1+ 1 9 #1 #3B #1A 42 2 4 12 Ν0ΝΕ **THE BEST HITS F0LL0W (THE 0NES DIGIT ALS0 APPEARS IN CHEMICALAND SPECTRAL PLAY BACK) SC0RE LABEL AMOCO 533 ANTIOXIDANT (2,6-DI-tert-BUTYL-p-CRESOl) S40264 1 992 2,6-DI-tert-BUTYL-p-CRESOL 2 979 S00283 2,6-Dl-tert-BUTYl-p-CRESOL 3 954 SPOT36 4 936 SI 9938 5 927 SJOltl 6 908 SL0162 7 908 S00540 2,6-DI-tert-BUTYL-p-CRESOL 8 908 SP0031 SR0274 9 908 10 905 SC1849 11 904 S09510 S37187 12 902 CATALIN ANTIOXIDANT CAO-1 (2,6-DI-TERT-BUTYL-p-CRESOl) 13 900 SP0090 SR0559 14 899 SI 4402 15 895 16 895 SP0134
SPECTRA 5.5 - + 5.6 - + 5.7 - + 5.8 - + 0 0 5.9 - + 4 9 6.0 - + 6.1 -* + 9 6.2 9 2 4567 90 *+ 6.3 -* + 6.4 - + 6.5 - + 7 6.6 - + 5 6.7 -* + l 6 90 6.8 *+ 234567 9012 5 78 0 6.9 56 9 1 4 678 0 *+ 7.0 * + 1234 789 23 5 7 9 7.1 9 1 78 0 *+ 4 7.2 * + 123 7890 234 7 7.3 * + l 456 9 3 6 8 7.4 * + 234 78 0 2345 7.5 5 90 4 7 90 *+ 7.6 * + 2 56 0 23 5678 7.7 * + l 34 78901 3 7 90 7.8 5 4 0 *+ 7.9 8 0 * + l 34 6 0 2 8.0 78 012 567 9 *+ 2 8.1 90 34567 0 *+l 4 8.2 * + 2345678 12 56 89 8.3 8 01 34 *+l 3 8.4 * + 2 56 90 2 4 7890 8.5 0 5 + 8.6 12 4 678 0 *+ 45 8.7 * + 12 5 78 3 8 0 8.8 0 7 9 * + 34 8.9 6 89 3 56 *+l 9.0 * + 23 7 1 4 789 9.1 5 0 + 9.2 56 + 9.3 + 4 6 01 9.4 9 1 0 + 9.5 + 9.6 7 *+ 4 9.7 6 8 0 8 2 *+l 9.8 - + 34 7 9 1 89 9.9 - + 6 2 10.0 - + 4 10.1 - + 0 10.2 - + 7 10.3 - + 0 2 10.4 - + 10.5 - + 9 7 0 6 10.6 4 *+ 10.7 12 *+ 10.8 9 5 *+ 10.9 0 + 11.0 + 11.1 0 *+ 11.2 12 4 78 *+ 11.3 * + l 3 78 0
Figure 6. Output f r o m S a d t l e r ' s IRIS s p e c t r a l s e a r c h p r o g r a m 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-fert-butyl-p-cresol
igin. Even quite weathered samples have been identified in this fashion, and the sources of every spill investi gated 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 prob lems. Although the sensitivity of most infrared spectrophotometers is not sufficiently high to allow drugs to be
rapidly identified by using blood or urine samples from overdose patients, IR does provide a rapid means of iden tifying the active ingredient of the pill or capsule that might have caused this overdose. Sadtler Research Laborato ries has published a collection of the spectra of commonly abused drugs, for which the samples were prepared by extracting prescription drug formula tions with alkaline and acidic chloro form; this technique usually leaves the great majority of all fillers and binders
1210 A · ANALYTICAL CHEMISTRY, VOL. 46, NO. 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 identifi cation 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 cat egory under which the drug may be classified (Figure 7). In most cases, only a few compounds fall into each
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category so that a rapid comparison with two or three reference spectra usually leads to an unambiguous iden tification. 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 so lution of several criminal cases (7). In forensic studies of a different type, IR spectroscopy has been used for identifying certain pigments in an cient paintings and distinguishing these from forgeries. Whereas inor ganic pigments can be readily recog nized by X-ray diffraction or optical emission spectroscopy, organic pig ments cannot; for these materials in frared spectroscopy provides a sensi tive alternative technique which has been applied successfully several times in the past (8 ). The identifica tion of paint samples has also proved to be important in police forensic lab oratories; for example, paint chips from automobiles involved in acci dents have been characterized by using a micro-ATR accessory (9). ATR spectroscopy is particularly use ful for identifying black paints con taining carbon black, since the mea sured spectrum depends essentially on the paint base. Another sampling technique for pigments involves tak ing a suspension of the paint in a suit able solvent, such as petroleum ether, and filtering the suspension through a Millipore R filter. After drying, the fil ter is placed on an ATR plate, and the spectrum of the pigment is measured (10). Particulate toners and extenders in writing inks, and even colloidal par ticles 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
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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 ad sorbed molecules, to determine differ ences in adsorption sites, and to study the reactivity of surfaces. Recently, catalytic silica surfaces have been modified by reaction with active or ganic molecules such as organosilanes; IR has been most helpful in following these reactions and checking the sta bility of the reaction products. In other work, described at the FACSS meeting by Charles Angell of Union Carbide Research Laboratories (11), the reaction of alcohols with free silanol 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 stud ied. In studies with other types of cata lytic materials, finely powdered met als have been dispersed in silica and alumina, thereby providing a large surface area on which gases can be ad sorbed. 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 at different ori entations of the crystal faces (14); 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 tech niques for the qualitative and quanti tative analysis of polymeric materials. Because of the different physical properties of polymers, several differ
1212 A · ANALYTICAL CHEMISTRY, VOL. 46, 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 poly mer), 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 at which the poly mer softens); ATR and pyrolysis tech niques have also been applied to the analysis of polymers. To aid in the rapid identification of polymers, flow charts have been developed (16) simi lar to the one shown earlier for the identification of drugs from their in frared spectra. Besides the simple identification of polymers, infrared spectroscopy can be used to determine their stereo chemistry, the types of additives, the degree of degradation by weathering, the presence of a copolymer, and the chain length, orientation, and crystalunity of a polymer. For example, in the spectrum of poly-(isobutylene) shown in Figure 8 (A), the doublet at 1390 and 1365 c m - 1 has been assigned to the t -butyl end-groups. By deter mining the relative intensity of these bands and the band centered at 1470 c m - 1 , 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 at 460 c m - 1 and the very weak band at 540 c m ' 1 are due to crystalline isotactic poly-(propylene). Many of the types of analysis listed above are suitable for automa tion, and Edward Brame of Du Pont recently described how his group auto mated a commercial infrared spectro photometer for polymer analysis (17). 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 sol vent and separate the additives by col umn chromatography. Pyrolysis tech-
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niques will often yield a distillate which is highly characteristic of the parent polymer, while the pyrolysis of elastomers such as rubbers and adhesives has allowed the identification of stabilizers, antioxidants, and accelera tor materials as well as the parent elastomer. Although the photometric accuracy of infrared spectrophotometers has seldom been regarded in the past as being high enough to permit quantita tive analysis to be performed to an ac curacy greater than ±1%, they are now being used in some industrial labora tories to obtain results at somewhat higher accuracy than this. One exam ple of such a determination is the analysis of the relative quantities of the monomer units of a poly-(methyl methacrylate-acrylonitrile), MMAAN, copolymer. The use of solutions always allows the most accurate re sults to be obtained by infrared spec troscopy, since samples of known con centration can be contained in a cell of known path length. MMA-AN readily dissolves in dimethyl sulfoxide, the spectrum of which is essentially free of absorption bands between 1650 and 2400 c m - 1 . The amount of methyl methacrylate is determined by using the carbonyl stretching mode at 1730 cm - 1 , and the acrylonitrile is deter mined by using the nitrile stretching
mode at 2240 cm - 1 . After calibration curves have been set up by measuring the spectra of MMA-AN copolymers of known composition, extremely ac curate determinations of the copoly mer can be rapidly performed. A severe analytical problem con cerning a newly developed food pack aging material was recently described (18), in which the extremely small (10-50 ppb) amount of polymer dis solved from a nitrile rubber modified acrylonitrile-methyl acrylate polymer had to be quantitatively determined to satisfy FDA requirements. The minute residue remaining after the solvent had been evaporated leaving the soluble fraction of the polymer was redissolved and evaporated on KBr. Analysis for the low levels of polymer in the micropellet still re quired 10X ordinate scale expansion on the grating spectrophotometer used for this measurement. Automotive Industry
In the same issue of ANALYTICAL CHKMISTRY in which the previous de termination was described, Lynn Lewis of General Motors Research Laboratories described several appli cations in which IR spectroscopy is used in the automotive industry (19). For example, in the area of product assurance, IR spectra of shipments of
1214 A · ANALYTICAL CHEMISTRY, VOL. 46, NO. 14, DECEMBER 1974
engine oil are routinely measured to detect possible deviations in the base oil and additive content. In a less rou tine analysis, the amount of synthetic rubber (styrenebutadiene copolymer) in dustfall and aerosol samples collect ed near a highway was determined. Gross organic materials were first ex tracted from the sample with benzene, after which the tire rubber was solubilized with o- dichlorobenzene in the presence of oxygen and cast as a film for measurement by IR spectroscopy. Enter FTS
All of the measurements which have been described above were made with grating spectrophotometers, but re cently Jack Koenig of Case Western Reserve University has described some very elegant applications of Fou rier transform spectroscopy in macromolecular research (20—22). He has obtained interesting new data on subjects such as the drawing of poly ethylene, the fracture of polystyrene, radiation cross-linking of polymers, and carbon-filled rubbers (Figure 9). For example, he has been able to study changes in certain infrared ab sorption bands caused when carbon black is added to rubber and when plasticizers are added to PVC (Figure 10).
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Figure 9. Comparison of spectrum of carbon-filled rubber sample (A) as measured by grating spectrophotometer and (B) as measured by Fourier transform spectropho tometer (reproduced f r o m ref. 22; copyright 1974, McLean-Hunter Ltd.)
Figure 10. Infrared s p e c t r u m in c a r b o n to-carbon double-bond stretching region for (A) carbon-filled and (B) unfilled polybutadiene (Reproduced f r o m ref. 22; copyright 1974, McLean-Hunter Ltd.)
F u t u r e of I n f r a r e d
At this point, it would be possible to e n u m e r a t e m a n y further applications of IR spectroscopy, industry by indus try. Suffice it to say a t this point t h a t in spite of t h e editorial views ex pressed in this JOURNAL, infrared spectroscopy is very m u c h alive in t h e industrial analytical laboratory a n d shows every evidence of holding its own against competitive i n s t r u m e n t a l
techniques. New developments in in frared i n s t r u m e n t a t i o n are still very evident. T h e inexpensive IR analyzer can be used for t h e q u a n t i t a t i v e analy sis of a variety of samples, for a m b i e n t air monitoring, a n d for process con trol. For t h e laboratory, small grating spectrometers are being m a d e more sensitive with little increase in price. However, in t h e (admittedly biased) opinion of this author, t h e major ad vance of t h e p a s t year has been seen in the development of Fourier transform spectrometers designed with t h e in dustrial analytical chemist in m i n d . Extremely versatile i n s t r u m e n t s with a price tag a r o u n d $40,000 were shown a t t h e recent F A C S S meeting, while an even cheaper special-purpose interferometric spectrometer for t h e on line analysis of nanogram quantities of compounds eluting from a gas chrom a t o g r a p h (Spectrotherm Corp., 3040 Olcott St., S a n t a Clara, Calif. 95051) was also introduced for t h e first t i m e a t this meeting. Infrared spectroscopy is certainly not entering a period of senescence, nor is it merely maintaining its repu tation as an analytical workhorse; rather, it is becoming one of t h e more exciting areas of analytical research. References
(1) H. A. Laitinen, Anal. Chem., 45, 2305 (1973). (2) T. Hirschfeld and G. Wijntjes, Appl. Opt., 12,2876 (1973). (3) P. R. Griffiths, Anal. Chem., 46, 645A (1974). (4) R. L. Hudson, paper presented at 1st PACSS Meeting, Atlantic City, N.J., Nov. 1974. (5) C. W. Brown, ibid. (6) R. W. Hannah and S. C. Pattacini, "The Identification of Drugs from Their Infrared Spectra," Perkin-Elmer Appli cations Study No. 11, 1972. (7) R. H. Ellis, paper presented at 1st FACSS Meeting, Atlantic City, N.J., Nov. 1974. (8) J. S. Olin, M. E. Salmon, and C. H. Olin, Appl. Opt., 8, 29 (1969). (9) H. J. Walls, ibid., ρ 21.
1216 A · ANALYTICAL CHEMISTRY, VOL. 46, NO. 14, DECEMBER 1974
(10) "Microchemical and Instrumental Analysis," Millipore Corp., Bedford, Mass. (11) C. L. Angell, paper presented at 1st FACSS Meeting, Atlantic City, N.J., Nov. 1974. (12) L. H. Little, "Infrared Spectra of Ad sorbed Species," Academic Press, Lon don, England, 1966. (13) M. L. Hair, "Infrared Spectroscopy in Surface Chemistry," Marcel Dekker, New York, N.Y., 1967. (14) J. 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 Applications Study No. 13,1973. (16) R. E. Kagarise and L. A. Weinberger, "Infrared Spectra of Plastics and Res ins," Naval Research Lab, Rept. 4369, Washington, D.C., 1954. (17) E. C. Brame, paper presented at 1st FACSS Meeting, Atlantic City, N.J., Nov. 1974. (18) V. F. Gaylor, Anal. Chem., 46, 897A (1974). (19) L. L. Lewis, ibid,, ρ 867Α. (20) J. L. Koenig, Amer. Lab., 9 (Sept. 1974). (21) J. L. Koenig, paper presented at 1st FACSS Meeting, Atlantic City, N.J., Nov. 1974. (22) J. L. Koenig and D. L. Tabb, Can. Res. Develop., 7, 25 (1974).
P e t e r R. Griffiths is, an assistant pro fessor of analytical chemistry a t Ohio University a t Athens, Ohio. He ob tained his doctorate a t Oxford Univer sity a n d t h e n s p e n t two years working with Ellis Lippincott's group a t t h e University of Maryland. Following this, he worked as p r o d u c t specialist for Fourier transform spectroscopy with Digilab Inc., Cambridge, Mass., and t h e n as m a n a g e r of t h e Analytical Services Laboratory a t Sadtler Re search Laboratories, Inc., in Philadel phia. His c u r r e n t interests include t h e q u a n t i t a t i v e r e m o t e analysis of gases by infrared emission spectroscopy a n d the s t u d y of chromatographically sep arated fractions by F T S .
