History of Spectrophotometry at Beckman Instruments, Inc. - Analytical

Α. Ο. Beckman, W. S. Gallaway, W. Kaye, and W. F. Ulrich Beckman Instruments, Inc., P.O. Box C-19600, Irvine, Calif. 92713

History of Spectrophotometry at Beckman Instruments, Inc. On July 6,1976, the last DU-2 spectrophotometer was produced at Beckman Instruments, Inc. This occasion closed an era of prism instruments at Beckman. Within the past three years, a number of spectrophotometers having their genesis in the "early" days of commercial instrumentation have been replaced by totally new models. As these instruments pass into the realm of history, it is appropriate to identify t h e m and document references where details of these instruments can be found. Spectrophotometers have played a significant role in analytical chemistry and in the growth of Beckman Instru-

ments, Inc. In 1941 when the company was known as National Technical Laboratories (NTL) and employed 60 people, its major products were p H electrodes and meters. At t h a t time, spectrophotometry was just beginning to find widespread analytical application. Although the foundations of analytical spectrophotometry had been well established, the available spectrographs and visual instruments were difficult to use and consumed time and patience. Photoelectric methods in the visible and ultraviolet regions reduced these difficulties, but available phototubes required extremely high input impedance amplifiers.

Figure 2. Quartz Model Β spectrophotometer (DU predecessor) with cover re moved revealing tangent-bar mechanism for prism rotation Note rotating sample cell holder surrounding detector

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Ultraviolet Spectrophotometer P i o n e e r Efforts. T h e state of the art in 1940 has been well documented in the articles of Ralph Miiller (1). T h e only commercially available auto matic spectrophotometer was the General Electric Hardy instrument (2), b u t its high price and restricted wavelength range limited its use. T h e two most popular spectrophotometers were the Cenco "Spectrophotelometer", employing a grating monochromator, barrier cell detector, and galva nometer readout; and the Coleman Model DM spectrophotometer, utiliz ing a double grating monochromator, a photoemissive detector, and a p H meter readout. These instruments used an incandescent tungsten source and barely penetrated into the ultravi olet region required for some of the most pressing industrial analyses such as the determination of vitamin A. T h e classical assay for vitamin A in volved very slow and laborious animal feeding tests. As early as 1928, scien tists had recognized t h a t vitamin A absorbed in the 320-330-nm region (3). During the 1930's interest in vita mins increased dramatically, and at least five photometers were developed specifically for vitamin A analysis (4). All used line emission sources, which rendered t h e m inapplicable to the ma jority of ultraviolet analyses. Scien tists desiring ultraviolet photoelectric instruments had to build their own. An example of this pioneering effort is described in the paper of Hogness et al. (5).

Report

Figure 1. Employees of National Technical Laboratories at a Christmas party, 1940 A. O. Beckman is in back row at extreme left. Warren Baxter is wearing glasses and appears in back row just to right of center. Roger Hayward and Howard Cary are standing 4th and 3rd, respectively, from right. Douglas Marlow is 9th from left in front row. Willis Humphrey, standing 8th from right, and Duane Foster, 2nd from right in front row, have played a significant role in the manufacture of DU and DU-2 in struments right up to the present

Model D U . In 1940 no one at Na tional Technical Laboratories had any extensive experience in spectropho tometry (Figure 1). T h e fact was rec ognized, however, t h a t the amplifier of the Beckman p H meter was well suit ed for use with vacuum-type photo tubes. T h e company began a spectro photometer development program in early 1940, and the responsibility for this program was assigned to H. H. Cary. Consulting assistance was sought from recognized optical ex perts, b u t World War II was under way and experts were hard to find. Roger Hayward, a professional archi tect and amateur scientist with some optic experience from his association with the Mount Wilson Observatory, provided a needed link to monochromator technology. His genius for quickly translating ideas into useful sketches was partially responsible for the extreme rapidity with which the DU spectrophotometer was developed. Douglas Marlow provided proficiency in mechanical design. T h e first instrument designed was a glass Fery prism instrument, but its performance was not considered suit able. A quartz prism Littrow design with a tangent-bar drive followed and was designated the Model Β (not to be confused with the Model Β glass Fery prism instrument later produced). Of the two quartz Model Β instruments produced, one was sold to the Chemis try D e p a r t m e n t of the University of California of Los Angeles in February 1941, and the other is in the compa

ny's historical museum. This instru m e n t utilized a tangent-bar mecha nism (Figure 2) which provided a sub stantially linear wavelength scale. Un fortunately, the scale was too com pressed, particularly in the ultraviolet region, and was replaced by a Model C

(Figure 3) with its innovative scroll drive, which was used in all subse quent Beckman quartz prism monochromators. Of the three Model C in struments produced, California Insti tute of Technology, Vita Foods Co., and Riverside Experiment Station

Figure 3. Quartz Model C spectrophotometer (DU predecessor) with Model G pH meter readout ANALYTICAL CHEMISTRY, VOL. 4 9 , NO. 3, MARCH 1977 ·

281 A

each purchased one. T h e Cal Tech in strument was later returned to the company for its museum. Both the Model Β and C instru ments were designed without electron ics; operators were expected to use a Beckman p H meter as amplifier and readout. It quickly became apparent that having the amplifier and readout in separate housings was economically and technically undesirable. When these components were incorporated within the monochromator, the instru ment was designated the Model D. T h e first of these instruments was shipped to Arthur H. T h o m a s Co. in Philadelphia on July 12,1941, and was used as a demonstrator at the Ninth Summer Conference on Spectroscopy a t the Massachusetts Institute of Technology, July 21-23,1941. T h e original paper describing the Model D, written by Cary and Beckman (6), was presented at M I T by Ε. Β. Patterson, Jr., of Arthur H. T h o m a s Co., because of wartime travel problems. Within a little more t h a n 14 months, a land mark instrument had been designed t h a t was to remain unsurpassed in its field for 35 years. Introduction of the Model D instru m e n t required the development of light sources as well as the monochro mator. T h e only known source of an ultraviolet continuum was the molecu lar hydrogen lamp, but no commercial source of suitable hydrogen lamps was known. A new type of lamp structure with an enclosed anode and thin blown window resulted from this de velopment (7). Hydrogen lamps and lamp power supplies were first deliv ered in December 1941. Another serious problem periodical ly plaguing the manufacture of the in struments was the supply of quartz for the prisms. Although Brazil, essential ly the only source of acceptably large ultraviolet transparent and untwinned quartz crystal, snipped a reasonable quantity of this material to the U.S., the quartz was quickly purchased for use in radio oscillators. Only after es tablishing a wartime priority listing and paying a premium price was it possible to get access to the stores of large, uncut crystals from which prism blanks passing the stringent optical specifications could be cut. T h e fourth major hurdle in produc ing the Beckman quartz spectropho tometer was the phototube detector. T h e RCA type 919 and Continental Electric Co. type 31V cesium oxide phototubes were commercially avail able and suitable for use in the 6001200-nm region. T h e RCA type 929 phototube was acceptable in the blue region, but no standard production of good detectors for the region below 350 nm existed. Limited quantities of an experimental (type C7032) photo

tube were available from RCA and showed promise of useful operation to 220 nm. However, individual photo tubes varied considerably in sensitivi ty. When regular production of the C7032 detector was a t t e m p t e d at RCA, the results were unacceptable, and the volume required for National Technical Laboratories, was not suffi cient to justify the needed develop ment effort. Yet the needed volume exceeded RCA's existing experimental production capability. When N T L ' s stock of C7032 tubes was exhausted, the spectrophotometer production line came to a near halt. T h e company began a crash program to develop ul traviolet detectors. Within a few months, in 1942, the Beckman type 2342 phototube was produced, and in struments incorporating it were desig nated the Model DU. H. H. Cary and Warren Baxter were the key partici pants in these programs. When it was introduced, the Model DU instrument had higher resolution and lower stray light in the ultraviolet than any other commercial instru ment, and it quickly enjoyed a good market. T h e first advertisement ap peared in the September 25,1941, issue of t h e News Edition of the American Chemical Society. By the end of 1941,18 instruments had been delivered; in the first six months of 1942, 54 instruments were delivered. For a small company (gross sales of $168 000 in 1940), this was a heady rise in business. In December 1941 the selling price of a DU with hydrogen lamp and power supply was $723.

Word of the DU's performance in analyses such as vitamin A spread quickly. T h e first paper to be p u b lished on the application of the DU to vitamin A appeared in t h e September 1942 issue of the Industrial and Engi neering Chemistry, Analytical Edi tion (8). Those decrying the present delays in publication will be interested to know t h a t the instrument upon which this paper was written was not shipped from Beckman Instruments until J u n e 5,1942! In subsequent years thousands of technical papers concerning DU applications have been published. Engineering on the DU and its ac cessories continued for over 28 years. T h e modular design facilitated the ad dition of accessories and t h e upgrad ing of components. T h e design also fa cilitated user modifications, account ing for a large number of instrumenta tion papers in the technical literature. Table I lists the major accessories and the dates of introduction. (Not includ ed are the numerous special cells and sample holders.) Some of the major accessories approached the complexity and cost of the basic spectrophotome ter. Only two of these accessories will be discussed in any detail in this brief history. One greatly expanded appli cation of the DU; the other resulted in near disaster. T h e first Beckman flame attach ment was introduced in 1947. Design of this instrument was begun by Gor don Locker and completed by P a u l Gilbert and R. C. Hawes (9). It con sisted of four basic components, an at-

Table I. Major Accessories for Model DU Name

Cat. no.

Introduction

UV accessory set

2 501

1941

Diffuse reflectance assembly

2 580

1942

Total fluorescence accessory

2 880

1947

Flame attachment

10 300

1948

Flame attachment

9 200

1951

Battery power regulator

1 900

1951

Photomultiplier attachment

4 300

1951

Spectral energy recorder

92 300

1955

DU power supply

23 700

1957

6 871

1959

Dual-source housing Spectral fluorescence attachment

22 850

1959

AC power supply

73 600

1961

Atomic absorption accessory

130 000

1965

Digital direct reader

109 8 0 2

1968

Concentration converter

131 900

1968

Data printer

134 109

1968


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omizer, spray chamber, burner, and control unit, and sold in 1948 for $750. Paul Gilbert continued to improve this accessory and by 1951 had per fected an atomizer burner t h a t gave superior performance plus reduced size and lowered costs ($395) (10). This burner has been supplied with many instruments, Beckman and nonBeckman, and is still produced. When the DU was first developed, it required dry cells as well as a leadacid storage battery, at t h a t time a normal, acceptable requirement. Al though the storage battery functioned well in the automobile and was inex pensive, it proved troublesome under intermittent use in the laboratory. T h e trickle charger introduced in 1951 helped, but users and dealers began developing their own AC power supplies to eliminate the storage bat tery. Beckman made several a t t e m p t s to develop an acceptable power supply, but for Beckman the problem was far more complex. T h e challenge lay in developing a replacement for all the batteries and simultaneously accom modating all the existing DU's in the field. This necessitated development in one package of 10 separate, electri cally isolated supplies covering a range from 2 to 600 V with regulation better than 0.02%. A paper by Greenough et al. (11) was ultimately recognized as offering a method of accomplishing this goal. Greenough's principle of operation required the conversion of a regulated high-voltage DC source to AC with a multivibrator. T h e regulated highvoltage AC signal was then converted to the required voltages with a trans former followed by rectification to DC. By the use of multiple transform er secondaries, the separate electrical ly isolated power sources could be ob tained. T o economize the rectification step, the multivibrator frequency was initially set at 2 kHz. Four prototypes were built and passed the required specifications, but the supply emitted an objectionable whistle. T h e frequen cy was then raised above the audible range (ultimately to 20 kHz). Because of the insistent demand for AC operation, a fateful decision was made to make 250 units without fol lowing the normal procedure of first field testing a few instruments. Unfor tunately, because of subtle variations in distributed capacitance, no two in struments behaved exactly alike. Worse, the supplies began to fail in the field because of excessive internal heat. Although the power supplies failed within their warranty period, they lasted long enough to prove the princi ple of operation. Few users wanted to return to battery operation, b u t fail

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ure of the power supply units de pressed sales of both the power supplies and the basic spectrophotom eter. Eventually, of course, the prob lems were solved. Most of the DU's sold after 1958 were AC operated, and an effective quality control program prevented repetition of the power sup ply problem. T h e DU was only the first of a long line of spectrophotometers. Within a year after the first DU was delivered, work started on infrared spectropho tometers. Model D U - 2 , Successor. Scientific instruments are sensitive to style as well as function. Throughout its mar keting history, Beckman Instruments has successfully and continuously upgraded its instruments and has in troduced new models regularly. De spite this fact, the DU remained out wardly unchanged for 23 years. Other ultraviolet spectrophotometers had been introduced, but the demand for the high-precision, nonscanning ultra violet spectrophotometer persisted. T h e DU's successor would have to be able to perform the thousands of ana lytical procedures developed for the DU with a minimum of operator re training. Over the years, four major a t t e m p t s were made. T h e DU-2, introduced in 1964, was relatively little changed from the orig inal DU. T h e major revisions were in the styling and location of components for ease of manipulation (12). It ac cepted most of the earlier designed ac cessories, including the AC power sup ply· Accessories continued to be devel oped for the DU-2 as listed in Table I. T h e new accessories automated fixed wavelength absorption analysis. However, by 1972 the price of a digi tal, direct-reading DU-2 with AC power supply had risen to $7 885, which was not competitive with other integrated-circuit spectrophotome ters. When the DU-2 was discontinued in mid-1976, only the accessories de veloped before 1959 were still in pro duction. In all, over 30 000 DU and DU-2 instruments have been pro duced. Few scientific instruments have matched the 35-year commercial life enjoyed by the DU and DU-2, nor have many been so widely copied. Exact and near exact copies of the DU have been commercially produced in J a p a n , England, and Russia. T h e DU has also been supplied as a component in the spectrophotometers manufac tured by Process and Instrument Co., Warren Electronics, Inc. (subsequent ly incorporated within Perkin-Elmer Co.), and the Gilford Instruments Labs, Inc. Model D U R , Process. T h e first at t e m p t a t automating the DU was for

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a butadiene process application. Designated the D U R and introduced in 1945, it featured an amplifier, recorder, and solenoid activated valves coupling a flowing gas or liquid stream to the absorption cell. T h e D U R recorded changes in transmittance with time U3). Automated Instrument. Model DR. T h e DU proved to be an ideal instrument for quantitative absorption and flame emission measurements a t a fixed wavelength within t h e 2 0 0 1200-nm region, but it was poorly suited for t h e recording of transmittance spectrograms. For a while, it was t h e only commercial photoelectric instrument on which ultraviolet absorption spectra could be obtained, b u t with considerable labor. Production of a spectrogram from 220 to 1200 n m could require several hours of exhausting manipulation. One of t h e most active DÙ users, Parke-Davis Co., boasted of having accumulated its 10 000th UV spectra by 1950. Obviously, there was a need for automation. Between 1947 and 1954 a t least six different customer modifications for automating the production of absorption spectra with t h e DU were described in t h e literature (14, 15). T h e first response of Beckman Instruments to this need was the introduction, in 1953, of t h e DR spectrophotometer (16). By adding interlocked wavelength advance, slit width, sample changer, and recorder controls, the instrument produced point-by-point spectrograms in robot fashion. Unfortunately, this instrument suffered mechanical reliability problems and proved too slow to warrant t h e necessary correction effort. Production was discontinued in 1955. Automatic S c a n n i n g Instruments. Model DK-1. One of the customer modifications of t h e DU for automatic operation t h a t developed a t Tennessee Eastman Co. was selected for commercial production at Beckman (15). This modification was originally made to exploit t h e near-infrared region for t h e analysis of water (17). T h e DU wavelength scroll was calibrated to 2000 nm, b u t t h e detector was not capable of responding to radiation of wavelengths longer than 1200 nm. When a lead sulfide detector was employed, t h e quartz prism was found to have excellent dispersion in the near-infrared. Furthermore, t h e near-infrared spectra of almost all organic compounds were found surprisingly rich when sufficiently long (1-10 cm) path cells were used. This richness of spectral detail compelled t h e development of automatic scanning instrumentation (15). T h e Beckman version of t h e Tennessee Eastman Instrument was called the DK-1 (Figure 4) in recognition of

Figure 4. Sample compartment (cover removed) of first Beckman fabricated prototype of DK spectrophotometer Source, monochromator, and phototube housing of DU were used intact

the design contribution made by Wilbur Kaye. Introduced in 1954, it utilized the DU monochromator with little modification except for a reduced height prism and an extended prism scroll carrying the wavelength range further into the infrared region. When the wavelength control was set to the infrared, visible light was doubly dispersed by t h a t portion of the prism opposite the exit slit. At first this portion of the prism was masked, but reducing the prism size proved a better solution. Years later it was found (again using vitamin A) t h a t a similar situation existed in the DU when the wavelength was set to around 330 nm and radiation of about 250 nm from the hydrogen lamp was doubly dispersed and detected. Prism height was then reduced in DU-2 instruments. T h e DK system employed two rotating mirrors coupled with a flexing wire shaft to give double-beam opera. tion. T h e beam was modulated at 15 Hz by the beam splitter and at 480 Hz by a chopper located before the monochromator. This permitted location of the sample after the monochromator for both UV and IR measurements. Slit width was servo-controlled from the reference signal while a strip chart recorder graphed the ratio of sample-to-reference signals. T h e flame and spectrofluorescence accessories designed for the DU were accepted by the DK instrument. T h e wavelength range for this instrument was ultimately extended to cover 160-3500 nm after large synthetic quartz crystals became available in 1959 U-8).

Model DK-2. T h e DK-2 was introduced a few months after the DK-1 (19). Originally it was intended to be an accessory to existing DU's, but conversion in the field proved difficult and it became an independent instrument. It differed from the DK-1 in utilizing a flatbed recorder mechanically coupled to the wavelength drive of the monochromator. This change permitted some cost savings and resulted in a more compact instrument. Both DK-1 and DK-2 instruments enjoyed a good market and were produced until 1975, when replaced by the ACTA line of instruments. Approximately 8000 DK-1 and DK-2 instruments were manufactured. Model DK-R. Among the specialized versions of the DK spectrophotometer, the one finding widest use was the DK-R introduced in 1957. It utilized an oscillating mirror and integrating sphere for the measurement of specular and diffused reflectance spectra (20). Model DK- U. T h e most elaborate of the DK line of instruments was the DK-U introduced in 1963. It combined the DK-1 with a second grating monochromator (21). T h e sample was located between the two monochromators, which permitted the recording of excitation as well as fluorescence, phosphorescence, and polarized fluorescence spectra. T h e grating monochromator also improved the recording of absorption and emission spectra because of the increased resolution and reduced stray light. T h e high cost of this instrument mitigated against its widespread use, but it introduced


the grating into the Beckman line of ultraviolet spectrophotometers. T h e DK-U, like the digital direct reading DU-2 and the dinosaur, was the end of the line. A better instrument required total redesign. Model B, Low-Cost Instrument. T h e DU was very well received by analysts and spectroscopists, but a need for a lower-cost instrument with reduced performance capabilities was recognized. A project was started in 1947 to develop a low-cost instrument covering the interval 320-1000 nm. A single source (tungsten) was employed with a glass Fery prism (22) designed so t h a t no separate collimator was required. It had two detectors on easily interchanged mounts. T h e electronics were integral with the monochromator, and a simple meter provided the direct readout of transmittance when normalized with a reference cell. T h e major accessories designed for the DU were accepted by the Model B. This instrument, introduced in 1949 and discontinued in 1974, holds the record for unmodified design at Beckman Instruments, Inc. D o u b l e - B e a m Instrument. Model DB. T h e basic ideas for the Beckman low-cost, double-beam spectrophotometer came from Sweden. T h e team of K.A.L. Akerman and K. E. Sundstrom had developed a novel approach to double-beam operation by placing the sample and reference cells between two vibrating mirrors (23). This system not only was less expensive than most others using rotating mirror systems, it also eliminated noncommon mirrors and thereby reduced the problems of obtaining and retaining a flat 100% line. T h e monochromator for this instrument was essentially a miniaturized version of the DU. T h e detector was a photomultiplier whose gain (dynode voltage) was established during each reference half cycle. This instrument was extensively tooled for volume production. Development spanned six years before its introduction in 1960. It was replaced by its grating twin, the DB-G, in 1968 (24). Later the electronics of the DB-G were transistorized by engineers in Beckman's Munich, Germany, plant. This version was designated the Model DB-GT. In terms of numbers of units manufactured, the DB, DB-G, and DB-GT instruments ranked second only to the DU. Infrared Instruments

Model IR-1. By the end of 1941, infrared spectrophotometry was beginning to be recognized as a potentially useful tool for chemical analysis. Three companies in particular were actively exploring infrared—Shell Development, Dow Chemical, and American Cyanamid. Following the bomb-

ing of Pearl Harbor, the United States embarked on a crash program to produce synthetic rubber. An urgent need arose for a quick, reliable way to determine the constituents, particularly butadiene, in complex gaseous mixtures encountered in petrochemical refineries. Infrared spectrophotometry was the answer. In early 1942 the Office of Rubber Reserve asked Beckman to produce IR spectrophotometers for the entire synthetic rubber program, no doubt in recognition of Beckman's recent success with the DU spectrophotometer. T h e ORR chose the IR instrument developed by Robert Brattain of Shell Development Co. as the basic model (25). Beckman shipped the first instrument to Shell on September 18, 1942 (Figure 5). It was a Littrow design with rock salt prism and galvanometer readout. T u r r e t stops for the prism arm permitted quick selection of 18 specified wavelengths. About 75 of these instruments were produced and delivered between 1942 and 1945. Model IR-2. In late 1942 work started on the design of an improved infrared spectrophotometer, the IR-2. T h e first instrument was delivered sometime prior to September 1945. This instrument borrowed heavily on the DU design. It was the first infrared instrument to use a chopped beam with AC electronics (26). Prior to this time, galvanometers were employed. These were slow and notoriously sensitive to vibration. AC operation also virtually eliminated the serious thermal zero drift of the DC instruments. This operation necessitated the development of fast responding thermocouples. Numerous other features made this instrument a favorite for quantitative analysis at selected wavelengths, and over 400 of these instruments were sold between 1945 and 1956. Unfortunately, the instrument did not produce a transmittance spectrum—a fatal flaw in view of the rich detail of infrared spectra. It might have enjoyed a long life for single-beam analysis had its operation been as simple as the DU. For years, however, the expense and the difficulties of working with very thin cells of hygroscopic rock salt kept the infrared spectrophotometer out of the control laboratory and in the hands of highly trained spectroscopists who preferred scanning, rather than selected wavelength instruments once they became available. Scanning IR Instruments. Model IR-3. T h e Model IR-3 m e t the demands of infrared spectroscopists for a scanning instrument. A large and expensive instrument featuring an evacuable double-prism monochromator and memory-type, direct-transmittance recording system, the first IR-3 290 A ·

Figure 5. IR-1 spectrophotometer with cover removed

was shipped to Shell Development Co. in 1949. T h e memory system was ingenious. It involved memorizing the slit width settings required to hold an output signal constant throughout a selected wavelength interval when a cell filled with a reference material was placed in the beam (27). A rescan of the wavelength interval using the previously memorized slit width program, but with a sample in the beam, resulted in a direct transmittance spectrum of the sample. In principle this was a very desirable mode of operation. In practice the design was ahead of its time. Over 100 vacuum tubes required constant maintenance, the mechanical demands upon the slit mechanism were very severe, and problems with the existing wire and tape recorders taxed the patience of the calmest user. Model IR-2T. In an effort to supply a lower-cost scanning infrared spectrophotometer, the memory system was adapted for the IR-2 monochromator. T h e resulting Model IR-2T, introduced in 1950 (28), did not solve any of the problems of the memory system and was less t h a n a market success. It did serve to make instrument experts out of a number of users.


1977

Model IR-2A. A much simplified method of producing qualitatively useful transmittance spectra with the IR-2 monochromator was achieved by an air purging system and mechanically coupled slit-to-wavelength drive (29). This instrument, the IR-2A, was introduced in 1955. Had this simple approach been used years earlier, it would probably have been well received, but within a year the Model IR-4 obsoleted this and all of the other IR instruments. T h e air purging system was retained for a number of years in the later infrared instruments. S i n g l e - B e a m / D o u b l e - B e a m Instrument. Model IR-4. T h e IR-4, conceived in late 1953 and introduced in February 1956, was the archetype of an evolutionary family of spectrophotometers which ultimately would span some 17 years of production (30). Numerous individuals contributed to the development program, but major credit for the final design goes to the team of William Ward, Lee Cahn, Joseph Ashley, and Norbert Kabuss. Based on a null balance, doublebeam system, the IR-4 represented a marked departure in design philosophy from its single-beam predecessors.

Although competitive double-beam instruments had been available for several years with growing success, resistance to this operating mode could still be found. Optical attenuators used in null balance systems gave rise to photometric errors which affected quantitative measurements. T h e field was also moving in new directions where speed and convenience were more desirable than exact quantitations. T o meet this a p p a r e n t dilemma, the IR-4 was designed to provide both operating modes, true single-beam and double-beam, selectable by a single panel switch. T h e optical system of the IR-4 included a double-prism monochromator similar to t h a t used earlier in the IR-3. However, the housing was purged of water vapor and carbon dioxide rather than evacuated. T h e prisms, Littrow mirrors, slit control mechanism, and wavelength dial formed an integral system which was kinematically mounted in the spectrophotometer so t h a t it could be readily removed and replaced with virtually no loss in wavelength accuracy. Interchanges with different prism materials (NaCl, KBr, LiF, CaF 2 ) were available, each stored in a thermostated box to assure immediate operation. Double-beam operation was obtained through the use of a synchronized double-chopper system. One chopper, used for recombining the sample reference beams after the sample compartment, could be disengaged to permit improved measurements on nonambient samples.

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Other new features in the IR-4 included push-button selection of scanning speed and chart drive, a flatbed recorder, an innovative slit program control, and an electrically coupled pen attenuator system which facilitated ordinate scale expansion. P r i s m / G r a t i n g IR Instruments. Model IR-7. T h e first major change in the IR-4 involved use of a grating in the second monochromator, providing a significant improvement in resolution. A novel cam system was used whereby one angular sweep of the prism was coupled to four sweeps of the grating (31a). This allowed use of the grating in four orders, providing a wide wavelength range while keeping the grating acceptably near the blaze angle. T h e first version of this instrument, the IR-7, was introduced in 1958. A sodium chloride prism was used with a 75 line/mm grating to cover the range 650-4000 c m - 1 . In 1960 a long wavelength interchange was made available for operation in the 200^700 c m " 1 range (31b). A cesium iodide prism and 30 line/mm grating were used. Model IR-9. T h e IR-9, another prism-grating instrument, was intro-

CIRCLE 205 ON READER SERVICE CARD


duced in 1962 with basically the same mechanical and electronic features of the IR-4 and IR-7 but with marked changes in the optical system (32). Use of a potassium bromide prism with two back-to-back gratings, each used in two orders, gave an expanded operating range of 400-4000 c m - 1 . More importantly from a design standpoint, a novel optical control disc was utilized which provided a significant improvement in wavenumber accuracy, e.g., about five times better than the IR-7. T h e control disc, securely m.ounted on the cam shaft, contained both the wavenumber scale and order break commands. Optical projection of the wavenumber scale gave an effective readout length of 13 m. T h e order break system provided highly reproducible grating changes and eliminated the gaps between these changes in the recorded spectra, an annoying factor in the IR-7 spectra. As with the IR-7, a cesium iodide prism-grating interchange was available for the IR-9. Introduction of Filters. Model IR11. T h e long wavelength interchanges of the IR-4, IR-7, and IR-9 were still limited by the prisms to frequencies greater t h a n 200 c m - 1 . A study by James E. Stewart showed how the IR-7 could be modified to operate at frequencies as low as 50 c m - 1 . A subsequent program to develop superior filters which could replace the prism as an order-sorter for the grating extended the range to 33 c m - 1 (33). This instrument, called the IR-11, was introduced in November 1963. Four gratings were mounted on a cube with each grating operating in the first order. A modified mercury arc was used as the source with a diamond window Golay detector. Model IR-12. Another spectrophotometer benefiting from the filter program was the IR-12 exhibited with the IR-11 at the 1964 Pittsburgh Conference. This instrument was essentially a replica of the IR-9 except for the grating arrangement and elimination of the prism. Four gratings mounted in the same cube arrangement as the IR-11 were used to provide an operating range of 200-4000 c m - ' . T h e IR-12 was the final major instrument in the IR-4 series. Production was finally terminated in 1972 in favor of a new generation of high performance instruments known as the IR 4200 Series. Low-Cost Instruments. IR-5 and IR-6. By 1955 it became apparent t h a t infrared spectroscopy would be more widely used if costs could be lowered and reliability increased, while the required operator skill was also reduced. This did not appear an impossible goal if performance specifications could be relaxed. Indeed, for many

molecular structure studies, the exist ing instruments were over-designed. T h e Beckman engineers were fully committed to the development of the IR-4; hence, a contract was drawn with the independent designer J. U. White for development of a "barebones" instrument consisting of a small prism monochromator and inte gral flatbed recorder (34). T h e instru ment was to operate in the singlebeam mode with a cam driven slit in a manner similar to t h a t used in t h e IR-2A. Unfortunately, its design un derestimated a serious problem. T h e sample was located between the mo nochromator and the detector. Since

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ble-beam instrument was introduced as the IR-5 in February 1957 and en joyed immediate success. Modest modifications led to the IR-5A which had a cesium bromide counterpart for use in the region 11-35 μ (35b). T h e single-beam instrument, called t h e IR-6, was discontinued shortly after its introduction in J u n e 1957. T h e two major competitors of in frared spectrophotometers, Baird As sociates and Perkin-Elmer, simulta neously introduced low-cost instru ments in 1957, and this effectively re moved infrared spectroscopy from t h e exclusive realm of the spectroscopist (36). T h e infrared spectrophotometer thus moved into the organic chemistry and production control laboratories. F i l t e r / G r a t i n g Instruments. IR-8. Like the IR-4, the IR-5 was only the first of a series of related instru ments. T h e IR-8, introduced in 1963, was a filter-grating version with an op erating range of 2.5-16 μ. Two gratings were used with four long-pass interfer ence filters. IR-10. In 1964 an extended-wave length companion to the IR-8 was in troduced as the IR-10. Two gratings, one used in two orders, were employed in conjunction with six long-pass transmission filters. T h e spectral pre sentation of the IR-10 was linear in wavenumbers (300-4000 c m - 1 ) , whereas both the IR-5 and IR-8 were linear wavelength instruments. IR-18/IR-20. Improved versions of the IR-8 and IR-10 were introduced in 1968 as the IR-18 and IR-20. Both instruments provided linear wavenumber presentations with no order gaps in the recorded spectra. Com pared to their predecessors, the IR-18 and IR-20 provided the operator with greater command of operating param eters and approached the versatility of research grade systems. Modest modifications led to the introduction of the IR-18A and IR-20A in 1970 and the IR-18AX and IR-20AX in 1972, shortly before the IR-5 family was dis continued. Rapid-Scan Instrument. IR-102. An interesting development in in frared interference filters led to a novel rapid-scan instrument intro duced in 1965, the IR-102. T h e mono chromator of the IR-102 consisted of a wheel on which were mounted three circular variable interference filters, one for the 2.5-4.5-μ region, one for the 4.4-8.0-μ region, and the third for the 7.9-14.5-μ region (37). Rotation of the wheel provided a progressive change in wavelength through the exit slit. Spectral resolution of this simple system approached t h a t of a conven tionally sized rock salt prism. T h e IR-102 was designed as a sin gle-beam system with complete scans over its entire range accomplished in

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Figure 6. Bar chart showing commercial life-span of Beckman spectrophotometers either 5 or 12.5 s. Heated gas cells were used for sampling, since the prin cipal purpose of the system was for analyzing eluted fractions from a gas chromatograph. Although the IR-102 did not enjoy a long or prosperous life because of sensitivity limitations, it paved the way for more conventional spectrophotometers utilizing the vari able filter. Major credit for the IR-102 and its immediate offspring goes to G. T. Keahl who also spearheaded devel opment of IR-4 and IR-5 successors. Microspec. A double-beam counter part of the IR-102 was introduced in February 1966 as a low-cost spectro photometer. Designated the "Micros pec", this instrument was comparable to the IR-5 in performance. T h e name "Microspec" alluded to the small beam size at the sample site which al lowed micro specimens to be analyzed on a routine basis (38). IR-33. Although the Microspec per formed as expected, the infrared field had grown accustomed to the high res olution afforded by gratings. In recog nition of this, a grating used in two or ders was added to the basic Microspec system, thus providing a high-perfor mance, double-beam spectrophotome ter at a reasonably low price. This unit was designated the IR-33 and became the forerunner of the AccuLab family of spectrophotometers still in produc tion, all utilizing a rotating wedge fil ter in conjunction with a grating. In the 35 years spanned by these in struments (Figure 6), the spectropho tometer has become a commonplace laboratory tool. T h e vacuum tube which ushered in many of the marvels of instrumentation is now obsolete. Prism dispersers are used only in spe

CIRCLE 65 ON READER SERVICE CARD 296 A · ANALYTICAL CHEMISTRY, VOL. 4 9 , NO. 3, MARCH

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cial applications. T h e grating and mi croprocessor now dominate the com mercial spectrophotometer field while the interferometer and tuned laser gain devotees. In time, even these ap proaches may be replaced in the search for the most economic solution for the analyst's needs. Acknowledgment T h e authors appreciate the many interviews with participants in this story. Special thanks go to Duane Fos ter who has been concerned with the manufacture of all the instruments de scribed here. References (la) R. H. Millier, Ind. Eng. Chem. Anal. Ed., 11,1 (1939). (lb) R. H. Millier, ibid., 12, 571 (1940). (le) R. H. MUller, ibid., 13, 667 (1941). (2) A. C. Hardy, J. Opt. Soc. Am., 28, 360 (1938). (3) R. A. Morton and I. M. Heilbron, Riochem.J., 22,987 (1928). (4a) R. L. McFarlan, J. W. Reddie, and E. C. Merrill, Ind. Eng. Chem. Anal. Ed., 9,324(1937). (4b) A. E. Parker and B. L. Oser, ibid., 13, 260(1941). (4c) B. Demarest, ibid., ρ 374. (5) T. R. Hogness, F. P. Zschiele, Jr., and A. E. Sidewell, Jr., J. Phys. Chem., 4 1 , 379 (1937). (6) H. H. Cary and A. O. Beckman, J. Opt. Soc. Am., 31,682(1941). (7) H. H. Cary and W. P. Baxter, U.S. P a t ent 2,463,743 (Dec. 29, 1945). (8) K. Morgareidge, Ind. Eng. Chem. Anal. Ed., 14,700(1942). (9) P. T. Gilbert, Jr., R. C. Hawes, and A. O. Beckman, Anal. Chem., 22, 772 (1950). (10) P. T. Gilbert, Jr., U.S. P a t e n t 2,714,833 (Apr. 19, 1950). (11) M. L. Greenough, W. E. Williams, and J. K. Tavlor, Rev. Sci. Instrum., 22, 484 (1951). (12) Anal, Chem., 36, 127A (1964).

(13) Α. Ο. Beckman, Instrumentation, 1 (5), 16 (1945). (14a) T. Coor, Jr., and D. C. Smith, Rev. Sci. Instrum., 18, 173 (1947). (14b) R. H. Millier, Anal. Chem., 25, 23A (Julv 1953). (14c) H. W. Etzel, J. Opt. Soc. Am., 43, 87 (1953). (14d) C. C. Yang and V. Legallais, Rev. Sci. Instrum., 25, 801 (1954). (14e) G. L. Royer, H. C. Lawrence, S. P. Kodama, and C. W. Warren, Anal. Chem., 27,501 (1955). (15) W. Kaye and R. G. Devaney, J. Opt. Soc. Am., 42,567 (1952). (16) L. Cahn and G. Gale, "Several Meth ods of Automatic Spectrophotometry", paper presented at the Symposium on Molecular Structure and Spectroscopy, Ohio State University, Columbus, Ohio, June 19, 1953. (17) W. Kaye, J. Opt. Soc. Am., 41, 277 (1951). (18) W. Kaye, Appl. Spectrosc, 15, 89 (1961). (19) L. Cahn and B. D. Henderson, J. Opt. Soc. Am., 48,380(1958). (20) B. D. Henderson, U.S. Patent 2,992,588 (Feb. 3, 1958). (21) W. Kaye, Appl. Opt., 2, 1295 (1963). (22a) W. C. Miller, U.S. Patent 2,594,344 (Sept. 24,1949). (22b) W. C. Miller, G. Hare, D. C. Strain, K. P. George, M. E. Stickney, and A. O. Beckman, J. Opt. Soc. Am., 39, 377 (1949). (22c) W. C. Miller and D. C. Strain, U.S. Patent 2,670,648 (Oct. 10, 1949). (23) K.A.L. Akerman and K. E. Sundstrom, U.S. Patent 2,868,060 (Mar. 22, 1954). (24) G. T. Keahl and J. D. McCallum, "Design and Performance of a New Fil ter-Grating Ultraviolet-Visible Spectro photometer", paper presented at the Pittsburgh Conf. on Anal. Chem. and Appl. Spectrosc, Cleveland, Ohio, Feb. 1966. (25a) R. R. Brattain and O. Beeck, J. Appl. Phys., 13,699 (1942). (25b) A. O. Beckman, Pet. Eng., 16,173 (Jan. 1945). (26a) H. H. Cary, U.S. Patent 2,562,525 (Jan. 14, 1947). (26b) H. H. Cary, R. C. Hawes, and K. P. George, U.S. Patent 2,607,899 (Jan. 14, 1947). (27a) R. G. Madsen, U.S. Patent 2,698,410 (June 15, 1950). (27b) R. G. Madsen and M. E. Stickney, U.S. Patent 2,741,941 (June 15, 1950). (27c) R. C. Hawes, H. H. Cary, A. O. Beck man, R. G. Madsen, G. H. Hare, and M. E. Stickney, "A Direct Transmittancy Recording Infrared Spectrometer", paper presented at the Symposium on Molecular Structure and Spectroscopy, Ohio State University, Columbus, Ohio, June 1949. (28) R. G. Madsen, M. E. Stickney, R. C. Hawes, and A. O. Beckman, "Memory Controlled Servomechanisms in a Re cording Infrared Spectrophotometer", paper presented at the Conf. of the In strument Soc. of Amer., St. Louis, Mo., Sept. 12-16, 1949. (29) R. H. Muller, Anal. Chem., 27, 23A (Aug. 1955). (30a) W. W. Ward and J. Ashley, U.S. Pat ent 2,948,185 (Feb. 24, 1958). (30b) R. H. Muller, Anal. Chem., 28, 73A (Feb. 1956). (31a) J. Ashley and W. W. Ward, "Design and Performance of an Automatic Dou ble-Beam, Prism-Grating Infrared Spec trophotometer", paper presented at the Pittsburgh Conf. on Anal. Chem. and Appl. Spectrosc, Cleveland, Ohio, Mar. 3-7, 1959. (31b) J. Ashley, "Design and Performance

of an Automatic Double-Beam, PrismGrating Infrared Spectrophotometer for Use Between 250 and 800 cm" 1 ", ibid., Feb. 29-Mar. 4, 1960. (32) J. Ashley and N. Shifrin, "A New Ex tended Range Infrared Spectrophotome ter", ibid., Mar. 1962. (33) G. T. Keahl, H. J. Sloane, and M. Lee, "Far Infrared Instrumentation—Second Generation", ibid., Mar. 1964. (34) R. H. Muller, Anal. Chem., 29, 55A (Jan. 1957). (35a) J. U. White, N. L. Alpert, S. Weiner, and L. Cahn, "Infrared Spectroscopy for the Chemical Laboratory", paper pre sented at the Pittsburgh Conf. on Anal. Chem. and Appl. Spectrosc, Cleveland, Ohio, Mar. 4-8, 1957. (35b) Ε. Ε. Buzza, "Design and Perfor mance of a New Infrared Prism Spectro photometer for the Cesium Bromide Re gion", ibid., Mar. 1961. (36) Anal. Chem., 29,19A (Feb. 1957). (37) G. T. Keahl, "Design of an Infrared Spectrophotometer for Use with Gas Chromatographs", paper presented at the Pittsburgh Conference on Anal. Chem. and Appl. Spectrosc, Cleveland, Ohio, Feb. 1966. (38) G. T. Keahl, "New Low-Cost Infrared Spectrophotometer", ibid.

to devote full time to instrument de velopment and manufacture. Dr. Beckman is recognized internationally for his leadership and contributions to science, education, industry, and envi ronmental technology.

William S. Gallaway is senior staff scientist at Scientific Instruments Di vision, Beckman Instruments, Inc., at Irvine, Calif. He graduated from the University of Michigan with a P h D in physics in 1941. Since joining Beck man Instruments in 1950, Dr. Galla way has specialized in the fields of ap plied spectroscopy and optical instru ment design and has done consider able work in the field of gas chroma tography. He has written some 15 technical papers, the majority of them dealing with infrared and optical in strument design. He is a member of the American Physical Society, Opti cal Society of Southern California, and the Southern California Associa tion for Applied Spectroscopy. Arnold O. B e c k m a n is chairman of the Board of Directors of Beckman In struments, Inc. Dr. Beckman founded the company in 1935 with the develop ment of the first Beckman instrument, a pH meter for measuring acidity and alkalinity. In 1940 he developed the Helipot helical potentiometer, a preci sion electronic component, and the quartz photoelectric spectrophotome ter, an instrument widely used in chemical analyses. Under his leader ship, Beckman has become one of the world's largest and most important makers of modern instrumentation and related products with sales in 1975 of $228.6 million. Dr. Beckman earned a BS degree in chemical engi neering in 1922 and a master's degree in physical chemistry in 1923 from the University of Illinois. He received his doctorate in photochemistry in 1928 at the California Institute of Technol ogy. He served on the Caltech chemis try faculty until 1940 when he began


Wilbur I. Kaye, research director 1956-1973, is currently senior scientist

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for the Scientific Instruments Division of Beckman Instruments, Inc., at Ir vine, Calif. He graduated from the University of Illinois with a P h D in chemistry in 1945 and has completed the Executive Program in Business Management at the University of Cal ifornia at Los Angeles. Dr. Kaye's fields of specialization include in frared and ultraviolet spectroscopy, molecular structure, x-ray diffraction, gas chromatography, electron micros copy, and light scattering. Currently, he is doing research on liquid crystals. T h e author or coauthor of 50 technical papers, Dr. Kaye was responsible for the original research and development on the Beckman DK series of record ing spectrophotometers. He is a mem ber of the ACS, the American Physical Society, Western Spectroscopy Associ ation, Society of Applied Spectrosco py, the American Association for the Advancement of Science, and Sigma Xi fraternity.

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William F. U l r i c h is manager of technical marketing support, Scientif ic Instruments Division of Beckman Instruments, Inc., at Irvine, Calif. Having received his P h D in inorganic chemistry from the University of Illi nois in 1952, he was employed by Shell Development Co. In 1956 he joined Beckman as a chemist, specializing in coordinating the development of new instrument techniques and assistance of customers with their application problems. Dr. Ulrich's research papers are concerned with analytical instru mentation, spectroscopy, and nuclear counting. He has served as councilor in the American Chemical Society and treasurer for the Society for Applied Spectroscopy. He is a member of A S T M E-13 Absorption Spectroscopy, E-30 Forensic Sciences, and E-34 Haz ardous Substances Committees, the American Association for Clinical Chemistry, and the Instrument Soci ety of America.

History of Spectrophotometry at Beckman Instruments, Inc. - Analytical

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