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DU spectrophotometer

January 01, 1970

The DU spectrophotometer or Beckman DU, introduced in 1941, was the first commercially viable scientific instrument for measuring the amount of ultraviolet light absorbed by a substance. This model of spectrophotometer enabled scientists to easily examine and identify a given substance based on its absorption spectrum, the pattern of light absorbed at different wavelengths. Arnold O. Beckman's National Technical Laboratories (later Beckman Instruments) developed three in-house prototype models (A, B, C) and one limited distribution model (D) before moving to full commercial production with the DU. Approximately 30,000 DU spectrophotometers were manufactured and sold between 1941 and 1976.

DU Spectrophotometer, National Technical Laboratories, 1947

Sometimes referred to as a UV–Vis spectrophotometer because it measured both the ultraviolet (UV) and visible spectra, the DU spectrophotometer is credited as being a truly revolutionary technology. It yielded more accurate results than previous methods for determining the chemical composition of a complex substance, and substantially reduced the time needed for an accurate analysis from weeks or hours to minutes. The Beckman DU was essential to several critical secret research projects during World War II, including the development of penicillin and synthetic rubber.

Background edit

Before the development of the DU spectrophotometer, analysis of a test sample to determine its components was a long, costly, and often inaccurate process. A classical wet laboratory contained a wide variety of complicated apparatus.[1] Test samples were run through a series of awkward and time-consuming qualitative processes to separate out and identify their components. Determining quantitative concentrations of those components in the sample involved further steps. Processes could involve techniques for chemical reactions, precipitations, filtrations and dissolutions.[2]: 150 [3] Determination of the concentrations of known impurities in a known inorganic substance such as molten iron could be done in under thirty minutes.[2]: 26  The determination of complex organic structures such as chlorophyll using wet and dry methods could take decades.[4] : 59–60 

Spectroscopic methods for observing the absorption of electromagnetic radiation in the visible spectrum were known as early as the 1860s.[4]: 65 [5]: 5  Scientists had observed that light traveling through a medium would be absorbed at different wavelengths, depending on the matter-composition of the medium involved. A white light source would emit light at multiple wavelengths over a range of frequencies. A prism could be used to separate a light source into specific wavelengths. Shining the light through a sample of a material would cause some wavelengths of light to be absorbed, while others would be unaffected and continue to be transmitted. Wavelengths in the resulting absorption spectrum would differ depending upon the atomic and molecular composition if the material involved.[6][7][8]

Spectroscopic methods were predominantly used by physicists and astrophysicists. Spectroscopic techniques were rarely taught in chemistry classes and were unfamiliar to most practicing chemists. Beginning around 1904, Frank Twyman of the London instrument making firm Adam Hilger, Ltd. tried to develop spectroscopic instruments for chemists, but his customer base was consistently made up of physicists rather than chemists. [9]: 113–118  By the 1930s he had developed a niche market in metallurgy, where his instruments were well adapted to the types of problems that chemists were solving.[9]: 124 

By the 1940s, both academic and industrial chemists were becoming increasingly interested in problems involving the composition and detection of biological molecules. Biological molecules, including proteins and nucleic acids, absorb light energy in both the ultraviolet and visible range.[10] The spectrum of visible light was not broad enough to enable scientists to examine substances such as vitamin A.[11] Accurate characterization of complex samples, particularly of biological materials, would require the accurate reading of absorption frequencies in the ultraviolet and infrared (IR) sections of the spectrum in addition to visible light. Existing instruments such as the Cenco "Spectrophotelometer" and the Coleman Model DM Spectrophotometer could not be effectively used to examine wavelengths in the ultraviolet range.[11][12]

The array of equipment needed to measure light energy reaching beyond the visible spectrum towards the ultraviolet could cost a laboratory as much as $3,000, a huge amount in 1940.[2]: 149  Repeated readings of a sample were taken to produce photographic plates showing the absorption spectrum of a material at different wavelengths. An experienced human could compare these to the known images to identify a match. Then information from the plates had to be combined to create a graph showing the spectrum as a whole. Ultimately, the accuracy of such approaches was dependent on accurate, consistent development of the photographic plates, and on human visual acuity and practice in reading the wavelengths.[2]: 150–151 

Development edit

The DU was developed at National Technical Laboratories (later Beckman Instruments) under the direction of Arnold Orville Beckman, an American chemist and inventor.[13][14] Beginning in 1940, National Technical Laboratories developed three in-house prototype models (A, B, C) and one limited distribution model (D) before moving to full commercial production with the DU in 1941.[5]: 6  Beckman's research team was led by Howard Cary, who went on to co-found Applied Physics Corporation (later Cary Instruments) which became one of Beckman Instruments' strongest competitors.[15] Other scientists included Roland Hawes and Kenyon George.[16]

Coleman Instruments had recently coupled a pH meter with an optical phototube unit to examine the visual spectrum (the Coleman Model DM).[10] Beckman had already developed a successful pH meter for measuring acidity of solutions, his company's breakthrough product. Seeing the potential to build upon their existing expertise, Beckman made it a goal to create an easy-to-use integrated instrument which would both register and report specific wavelengths extending into the ultraviolet range. Rather than depending on development of photographic plates, or a human observer's visual ability to detect wavelengths in the absorption spectrum, phototubes would be used to register and report the specific wavelengths that were detected. This had the potential to increase the instrument's accuracy and reliability as well as its speed and ease of use.[2]: 149–151 

Model A (prototype) edit

The first prototype Beckman spectrophotometer, the Model A, was created at National Technologies Laboratories in 1940. It used a tungsten light source with a glass Fery prism as a monochromator.[17]: 16 [18] Tungsten was used for incandescent light filaments because it was strong, withstood heat, and emitted a steady light.[19] Types of light sources differed in the range of wavelengths of light that they emitted. Tungsten lamps were useful in the visible light range but gave poor coverage in the ultraviolet range. However, they had the advantage of being readily available because they were used as automobile headlamps.[17]: 17  An external amplifier from the Beckman pH meter and a vacuum tube photocell were used to detect wavelengths.[17]: 16 

Model B (prototype) edit

 
Optical quality quartz crystals

It was quickly realized that a glass dispersive prism was not suitable for use in the ultraviolet spectrum.[2]: 153 [17]: 16  Glass absorbed electromagnetic radiation below 400 millimicrons rather than dispersing it.[20] In the Model B, a quartz prism was substituted for the earlier glass.[2]: 153 [17]: 16 

A tangent bar mechanism was used to adjust the monochromator. The mechanism was highly sensitive and required a skilled operator.[17]: 16  Only two Model B prototypes were made. One was sold: in February 1941, to the University of California Chemistry department in Los Angeles.[2]: 153 

The Model B prototype should be distinguished from a later production model of spectrophotometer that was also referred to as the Model "B". The production Model "B" was introduced in 1949 as a less-expensive, simple-to-use alternative to the Beckman DU.[21] It used a glass Fery prism as a chromator and operated in a narrower range, roughly from 320 millimicrons to 950 millimicrons, and 5 to 20 Å.[22]: 183–184 [23][24][25]

Model C (prototype) edit

Three Model C instruments were then built, improving the instrument's wavelength resolution. The Model B's rotary cell compartment was replaced with a linear sample chamber. The tangent bar mechanism was replaced by a scroll drive mechanism,[17]: 16  which could be more precisely controlled to reset the quartz prism and select the desired wavelength.[10] With this new mechanism, results could be more easily and reliably obtained, without requiring a highly skilled operator. This set the pattern for all of Beckman's later quartz prism instruments.[17]: 16  Although only three Model B prototypes were built, all were sold, one to Caltech and the other two to companies in the food industry.[2]: 153 

Model D (limited production) edit

 
Quartz photoelectric spectrophotometer, Cary & Beckman, 1941[26]: 687 

The A, B, and C prototype models all coupled an external Beckman pH meter to the optical component to obtain readouts. In developing the Model D, Beckman took the direct-coupled amplifier circuit from the pH meter and combined the optical and electronic components in a single housing, making it more economical.[10]

Moving from a prototype to production of the Model D involved challenges. Beckman originally approached Bausch and Lomb about making quartz prisms for the spectrophotometer. When they turned down the opportunity, National Technical Laboratories designed its own optical system, including both a control mechanism and a quartz prism. Large, high optical quality quartz suitable for creating prisms was difficult to obtain. It came from Brazil, and was in demand for wartime radio oscillators. Beckman had to obtain a wartime priority listing for the spectrophotometer to get access to suitable quartz supplies.[17]: 17 

Beckman had previously attempted to find a source of reliable hydrogen lamps, seeking better sensitivity to wavelengths in the ultraviolet range than was possible with tungsten. As described in July 1941, the Beckman spectrophotometer could use a "hot cathode hydrogen discharge tube" or a tungsten light source interchangeably.[26]: 684–685  However, Beckman was still unsatisfied with the available hydrogen lamps. National Technical Laboratories designed its own hydrogen lamp, an anode enclosed in a thin blown-glass window.[17]: 17  By December 1941, the in-house design was being used in production of the Model D.[2]: 154–155 

The instrument's design also required a more sensitive phototube than was commercially available at that time. Beckman was able to obtain small batches of an experimental phototube from RCA for the first Model D instruments.[17]: 17 

The Model D spectrophotometer, using the experimental RCA phototube, was shown at MIT's Summer Conference on Spectroscopy in July 1941. The paper that Cary and Beckman presented there was published in the Journal of the Optical Society of America. In it, Cary and Beckman compared designs for a modified self-collimating quartz Fery prism, a mirror-collimated quartz Littrow prism, and various gratings.[26]: 683  The Littrow prism was a half-prism, which had a mirrored back face, so that the light went through the front face twice.[18][27]: 31–34  Use of a tungsten light source with the quartz Littrow prism as a monochromator was reported to minimize light scattering within the instrument.[26]: 686 

The Model D was the first model to enter actual production. A small number of Model D instruments were sold, beginning in July 1941, before it was superseded by the DU.[2]: 153–155 [17]: 17–18 

Model DU edit

 
Disassembled absorption cell and photo-tube compartment, Cary & Beckman, 1941[26]: 687 

When RCA could not meet Beckman's demand for experimental phototubes, National Technical Laboratories again had to design its own components in-house.[17]: 18  They developed a pair of phototubes, sensitive to the red and blue areas of the spectrum, capable of amplifying the signals they received.[28]: 230  With the incorporation of Beckman's UV-sensitive phototubes, the Model D became the Model DU UV–Vis spectrophotometer.[17]: 18  Its designation as a "UV–Vis" spectrophotometer indicates its ability to measure light in both the visible and ultraviolet spectra.[29]

The DU was the first commercially viable scientific instrument for measuring the amount of ultraviolet light absorbed by a substance.[2]: 148  [5]: 10  As he had done with the pH meter, Beckman had replaced an array of complicated equipment with a single, easy-to-use instrument. One of the first fully integrated instruments[17]: 11  or "black boxes" used in modern chemical laboratories,[30] it sold for $723 in 1941.[12]

It is generally assumed that the "DU" in the name was a combination of "D" for the Model D on which it was based, and "U" for the ultraviolet spectrum. However, it has been suggested that "DU" may also reference Beckman's fraternity at the University of Illinois, Delta Upsilon, whose members were called "DU"s.[31]

A publication in the scholarly literature compared the optical quality of the DU to the Cary 14 Spectrophotometer, another leading UV–Vis spectrophotometer of the time.[32]

Design edit

 
Model DU spectrophotometer – exploded view, Beckman manual, 1954


From 1941 until 1976, when it was discontinued, the Model DU spectrophotometer was built upon what was essentially the same design.[12] It was a single beam instrument.[16]: 11 [33] The DU spectrophotometers used a quartz prism to separate light from a lamp into its absorption spectrum and a phototube to electrically measure the light energy across the spectrum. This allowed the user to plot the light absorption spectrum of a substance to obtain a standardized "fingerprint" characteristic of a compound.[2]: 151  [34][35] All modern UV–Vis spectrophotometer are built on the same basic principles as the DU spectrophotometer.[29]


 
Diagram of Model DU optical system, Beckman manual, 1954

"Light from the tungsten lamp is focused by the condensing mirror and directed in a beam to the diagonal slit entrance mirror. The entrance mirror deflects the light through the entrance slit and into the monochromator to the collimating mirror. Light falling on the collimating mirror is rendered parallel and reflected to the quartz prism where it undergoes refraction. The back surface of the prism is aluminized so that light refracted at the first surface is reflected back through the prism, undergoing further refraction as it emerges from the prism. The desired wavelength of light is selected by rotating the Wavelength Selector which adjusts the position of the prism. The spectrum is directed back to the collimating mirror which centers the chosen wavelength on the exit slit and sample. Light passing through the sample strikes the phototube, causing a current gain. The current gain is amplified and registered on the null meter." Model DU Optical System[36]: 3 

Although the default light source for the instrument was tungsten, a hydrogen or mercury lamp could be substituted depending on the optimal range of measurement for which the instrument was to be used.[36] : 3  The tungsten lamp was suitable for transmittance of wavelengths between 320 and 1000 millimicrons; the hydrogen lamp for 220 to 320 millimicrons, and the mercury lamp for checking the calibration of the spectrophotometer.[36]: 6 


 
Minimum spectral band widths, Cary & Beckman, 1941

As advertised in the 1941 News Edition of the American Chemical Society, the Beckman Spectrophotometer used an autocollimating quartz crystal prism for a monochromator, capable of covering a range from the ultraviolet (200 millimicrons) to the infrared (2000 millimicrons), with a nominal bandwidth of 2 millimicrons or less for most of its spectral range. The slit mechanism was continuously adjustable from .01 to 2.0 mm and claimed to have less than 1/10% of stray light over most of the spectral range. It featured an easy-to-read wavelength scale, simultaneously reporting % Transmission and Density information.[37]

The sample holder held up to 4 cells.[36]: 3 [37] Cells could be moved into the light path via an external control, allowing the user to take multiple readings without opening the cell compartment.[36]: 3  As described in the DU's manual, absorbance measurements of a sample were made in comparison to a blank, or standard, "a solution identical in composition with the sample except that the absorbing material being measured is absent."[36]: 24  The standard could be a cell filled with a solvent such as distilled water[36]: 24  or a prepared solvent of a known concentration.[27]: 30–31  At each wavelength two measurements are made: with the sample and with the standard in the light beam. This enables the ratio, transmittance, to be obtained. For quantitative measurements transmittance is converted to absorbance which is proportional to the solute concentration according to Beer's law. This makes possible the quantitative determination of the amount of a substance in solution.[38]

The user could also switch between phototubes without removing the sample holder. A 1941 advertisement indicates that three types of phototubes were available, with maximum sensitivity to red, blue and ultraviolet light ranges.[37]

The 1954 DU spectrophotometer differs in that it claims to be useful from 200 to 1000 millimicrons,[36]: 2  and does not mention the ultraviolet phototube.[36]: 3  The wavelength selector, however, still ranged from 200 to 2000 millimicrons.[36]: 4  and an "Ultraviolet accessory set" was available.[36]: 25  This shift away from using the DU for infrared measurement is understandable, since by 1954 Beckman Instruments was marketing a separate infrared spectrophotometer. Beckman developed the IR-1 infrared spectrophotometer during World War II, and redesigned it as the IR-4 between 1953 and 1956.[2]: 165 [39]: 6–7 

Use edit

 
Beckman DU spectrophotometer in use

The Beckman spectrophotometer was the first easy-to-use single instrument containing both the optical and electronic components needed for ultraviolet-absorption spectrophotometry within a single housing.[2]: 153  The user could insert a cell tray with standard and sample cells, dial up the desired wavelength of light, confirm that the instrument was properly set by measuring the standard, and then measure the amount of absorption of the sample, reading the frequency from a simple meter.[40] A series of readings at different wavelengths could be taken without disturbing the sample.[41] The DU spectrophotometer's manual scanning method was extremely fast, reducing analysis times from weeks or hours to minutes.[39]: 6  [42] [43]

It was accurate in both the visible and ultraviolet ranges.[29] Working in both the ultraviolet and the visible regions of the spectrum, the model DU produced accurate absorption spectra which could be obtained with relative ease and accurately replicated.[41] The National Bureau of Standards ran tests to certify that the DU's results were accurate and repeatable and recommended its use.[2]: 156 

Other advantages included its high resolution and the minimization of stray light in the ultraviolet region.[12] Although it was not cheap, its initial price of $723[12] made it available to the average laboratory.[44]: 501  In comparison, in 1943, the GE Hardy Spectrophotometer cost $6,400.[39]: 6  Practical and reliable, the DU rapidly established itself as a standard for laboratory equipment.[35]: 141 

Impact edit

 
World War II poster encouraged researchers to "Give this job Everything You've got"

Credited with having "brought about a breakthrough in optical spectroscopy",[5]: 10  the Beckman DU has been identified as "an indispensable tool for chemistry"[2]: 207  and "the Model T of laboratory instruments".[12] Approximately 30,000 DU spectrophotometers were manufactured and sold between 1941 and 1976.[5]: 11 [45]

The DU enabled researchers to perform easier analysis of substances by quickly taking measurements at more than one wavelength to produce an absorption spectrum describing the complete substance. For example, the standard method of analysis of the vitamin A content of shark liver oil, before the introduction of the DU spectrophotometer, involved feeding the oil to rats for 21 days, then cutting off the rats' tails and examining their bone structure. With the DU's UV technology, vitamin A content of shark liver oil could be determined directly in a matter of minutes.[39]: 6 

The Scripps Research Institute and the Massachusetts Institute of Technology credit the DU with improving both accuracy and speed of chemical analysis. MIT states: "This device forever simplified and streamlined chemical analysis, by allowing researchers to perform a 99.9% accurate quantitative measurement of a substance within minutes, as opposed to the weeks required previously for results of only 25% accuracy."[42][43]

Inorganic chemist and philosopher of science Theodore L. Brown states that it "revolutionized the measurement of light signals from samples".[46]: 2  Nobel laureate Bruce Merrifield is quoted as calling the DU spectrophotometer "probably the most important instrument ever developed towards the advancement of bioscience."[12] Historian of science Peter J. T. Morris identifies the introduction of the DU and other scientific instruments in the 1940s as the beginning of a Kuhnian revolution.[4] : 80 

For the Beckman company, the DU was one of three foundational inventions – the pH meter, the DU spectrophotometer, and the helipot potentiometer – that established the company on a secure financial basis and enabled it to expand.[47]

Vitamins edit

Development of the spectrophotometer had direct relevance to World War II and the American war effort. The role of vitamins in health was of significant concern, as scientists wanted to identify Vitamin A-rich foods to keep soldiers healthy. Previous methods of assessing Vitamin A levels involved feeding rats a food for several weeks and then performing a biopsy to estimate ingested Vitamin A levels. In contrast, examining a food sample with a DU spectrophotometer yielded better results in a matter of minutes.[48] The DU spectrophotometer could be used to study both vitamin A and its precursor carotenoids,[49] and rapidly became the preferred method of spectrophotometric analysis.[11][50][51]

Penicillin edit

The DU spectrophotometer was also an important tool for scientists studying and producing the new wonder drug penicillin.[10] The development of penicillin was a secret national mission, involving 17 drug companies, with the goal of providing penicillin to all U.S. Forces engaged in World War II.[52]: 312 [53] It was known that penicillin was more effective than sulfa drugs,[52]: 312  and that its use reduced mortality, severity of long-term wound trauma, and recovery time.[2]: 158  However, its structure was not understood, isolation procedures used to create pure cultures were primitive, and production using known surface culture techniques was slow.[52]: 312 

At Northern Regional Research Laboratory in Peoria, Illinois, researchers collected and examined more than 2,000 specimens of molds (as well as other microorganisms).[54] An extensive research team included Robert Coghill, Norman Heatley, Andrew Moyer, Mary Hunt,[55][56][57] Frank H. Stodola and Morris E. Friedkin. Friedkin recalls that an early model of the Beckman DU spectrophotometer was used by the penicillin researchers in Peoria.[52]: 316  The Peoria lab was successful in isolating and commercially producing superior strains of the mold, which were 200 times more effective than the original forms discovered by Alexander Fleming.[55] By the end of the war, American pharmaceutical companies were producing 650 billion units of penicillin each month.[55] Much of the work done in this area during World War II was kept secret until after the war.[2]: 158 [53]

Hydrocarbons edit

The DU spectrophotometer was also used for critical analysis of hydrocarbons. A number of hydrocarbons were of interest to the war effort. Toluene, a hydrocarbon in crude oil, was used in production of TNT for military use.[2]: 158–159 [17]: 19  Benzene and butadienes were used in the production of synthetic rubber.[58] Rubber, used in tires for jeeps, airplanes and tanks, was in critically short supply because the United States was cut off from foreign supplies of natural rubber.[2]: 158–159  The Office of Rubber Reserve organized researchers at universities and in industry to secretly work on the problem.[59] The demand for synthetic rubber caused Beckman Instruments to develop infrared spectrophotometers. Infrared spectrophotometers were better suited than UV–Vis spectrophotometers to the analysis of C4 hydrocarbons, particularly for applications in petroleum refining and gasoline production.[2]: 159 [4]: 17 

Enzyme assays and DNA research edit

Gerty Cori and her husband Carl Ferdinand Cori won the Nobel Prize in Physiology or Medicine in 1947 in recognition of their work on enzymes. They made several discoveries critical to understanding carbohydrate metabolism, including the isolation and discovery of the Cori ester, glucose 1-phosphate, and the understanding of the Cori cycle. They determined that the enzyme phosphorylase catalyzes formation of glucose 1-phosphate, which is the beginning and ending step in the conversions of glycogen into glucose and blood glucose to glycogen. Gerty Cori was also the first to show that a defect in an enzyme can be the cause of a human genetic disease.[60] The Beckman DU spectrophotometer was used in the Cori laboratory to calculate enzyme concentrations, including phosphorylase.[61]

Another researcher who spent six months in 1947 at the Cori laboratory, "the most vibrant place in biochemistry" at that time, was Arthur Kornberg.[62] Kornberg was already familiar with the DU spectrophotometer, which he had used at Severo Ochoa's laboratory at New York University. The "new and scarce" Beckman DU, loaned to Ochoa by the American Philosophical Society, was highly prized and in constant use. Kornberg used it to purify aconitase, an enzyme in the citric acid cycle.[62][63]

"The enzyme could be assayed in a few minutes by coupling it to isocitrate dehydrogenase and in measuring the NADH formed using the Beckman DU spectrophotometer, an instrument that transformed biochemistry."[63]: 113 

Kornberg and Bernard L. Horecker used the Beckman DU spectrophotometer for enzyme assays measuring NADH and NADPH. They determined their extinction coefficients, establishing a basis for quantitative measurements in reactions involving nucleotides. This work became one of the most cited papers in biochemistry.[63]: 115  Kornberg went on to study nucleotides in DNA synthesis, isolating the first DNA polymerizing enzyme (DNA polymerase I) in 1956 and receiving the Nobel Prize in Physiology or Medicine with Severo Ochoa in 1959.[64]

The bases of DNA absorbed ultraviolet light near 260 nm.[10] Inspired by the work of Oswald Avery[65] on DNA, Erwin Chargaff used a DU spectrophotometer in the 1940s in measuring the relative concentrations of bases in DNA.[66]: 260, 290–302  Based on this research, he formulated Chargaff's rules.[67] In the first complete quantitative analysis of DNA, he reported the near-equal correspondence of pairs of bases in DNA, with the number of guanine units equaling the number of cytosine units, and the number of adenine units equaling the number of thymine units. He further demonstrated that the relative amounts of guanine, cytosine, adenine and thymine varied between species. In 1952, Chargaff met Francis Crick and James D. Watson, discussing his findings with them. Watson and Crick built upon his ideas in their determination of the structure of DNA.[67]

Biotechnology edit

Ultraviolet spectroscopy has wide applicability in molecular biology, particularly the study of photosynthesis.[68] It has been used to study a wide variety of flowering plants and ferns[69] by researchers in departments of biology, plant physiology and agriculture science as well as molecular genetics.[70]

Particularly useful in detecting conjugated double bonds, the new technology made it possible for researchers like Ralph Holman and George O. Burr to study dietary fats, work that had significant implications for human diet.[71] The DU spectrophotometer was also used in the study of steroids[72][73] by researchers like Alejandro Zaffaroni,[74] who helped to develop the birth control pill, the nicotine patch, and corticosteroids.[75]

Later models edit

 
Beckman Model DK1 Ultraviolet Spectrophotometer

The Beckman team eventually developed additional models, as well as a number of accessories or attachments which could be used to modify the DU for different types of work. One of the first accessories was a flame attachment with a more powerful photo multiplier to enable the user to examine flames such as potassium, sodium and cesium (1947).[16]: 11 [28]: 230 

In the 1950s, Beckman Instruments developed the DR and the DK, both of which were double-beam ultraviolet spectrophotometers. The DK was named for Wilbur I. Kaye, who developed it by modifying the DU to expand its range into the near-infrared.[16] He did the initial work while at Tennessee Eastman Kodak, and later was hired by Beckman Instruments.[76] The DKs introduced an automatic recording feature. The DK-1 used a non-linear scroll, and the DK-2 used a linear scroll to automatically record the spectra.[76]: 21 

The DR incorporated a "robot operator" which would reset the knobs on the DU to complete a sequence of measurements at different wavelengths, just like a human operator would to generate results for a full spectrum. It used a linear shuttle with four positions, and a superstructure to change the knobs. It had a moving chart recorder to plot results, with red, green and black dots.[16] The price of recording spectrophotometers was substantially higher than non-recording machines.[72]

The DK was ten times faster than the DR, but not quite as accurate.[16] It used a photomultiplier, which had introduced a source of error.[76]: 21  The DK's speed made it preferred to the DR.[16] Kaye eventually developed the DKU, combining infrared and ultraviolet features in one instrument, but it was more expensive than other models.[76]

The last DU spectrophotometer was produced on July 6, 1976.[77] By the 1980s, computers were being incorporated into scientific instruments such as Bausch & Lomb's Spectronic 2000 UV–Vis spectrophotometer, to improve data acquisition and provide instrument control.[29] Specialized spectrophotometers designed for specific tasks now tend to be used rather than general "all-purpose machines" like the DU.[5]: 1 [78]

References edit

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  25. ^ "Beckman Instruments". Analytical Chemistry. 22 (12): 9A. December 1950. doi:10.1021/ac60048a708.
  26. ^ a b c d e Cary, H. H.; Beckman, Arnold O. (1941). "A Quartz Photoelectric Spectrophotometer". Journal of the Optical Society of America. 31 (11): 682–689. Bibcode:1941JOSA...31..682C. doi:10.1364/JOSA.31.000682.
  27. ^ a b Robinson, James W. (1996). Atomic spectroscopy (2nd ed.). New York: Dekker. pp. 30–33. ISBN 978-0-8247-9742-3. Retrieved 9 September 2016.
  28. ^ a b Gardiner, Kenneth (1956). "Flame photometry". In Berl, Walter G. (ed.). Physical Methods in Chemical Analysis (3 ed.). New York: Academic Press. pp. 219–290. ISBN 978-1-4832-5563-7. Retrieved 17 March 2016.
  29. ^ a b c d Buie, John (July 13, 2011). (PDF). Lab Manager. pp. 24–25. Archived from the original (PDF) on March 24, 2016. Retrieved March 17, 2016.
  30. ^ "Visible Proofs: Forensic Views of the Body". National Institutes of Health. Retrieved 14 March 2016.
  31. ^ "Beckman Model DU Quartz Spectrophotometer". Illinois Simulator Laboratory. Retrieved 29 August 2016.
  32. ^ Brode, Wallace R.; Gould, John H.; Whitney, James E.; Wyman, George M. (October 1953). "A Comparative Survey of Spectrophotometers in the 210–760 mμ Region". Journal of the Optical Society of America. 43 (10): 862–865. Bibcode:1953JOSA...43..862B. doi:10.1364/JOSA.43.000862.
  33. ^ Dulski, Thomas R. (1999). Trace elemental analysis of metals : methods and techniques. New York: Marcel Dekker. p. 195. ISBN 978-0-8247-1985-2. Retrieved 31 August 2016.
  34. ^ Jarnutowski, R.; Ferraro, J. R.; Lankin, D. C. (1992). "Fifty years of commercial instrumentation in absorption spectroscopy, part II. Landmark instruments in UV/vis". Spectroscopy. 7: 22–24, 26.
  35. ^ a b Zweig, Gunter (1976). Analytical Methods for Pesticides, Plant Growth Regulators, and Food Additives: Principles, Methods, and General Applications. New York: Academic Press. pp. 141–143. ISBN 978-0-12-784301-8. Retrieved 9 September 2016.
  36. ^ a b c d e f g h i j k Beckman Instruments Instruction Manual : The Beckman Model DU Spectrophotometer and Accessories. Fullerton, CA: Beckman Instruments, Inc. 1954.
  37. ^ a b c "Announcing an Important New Beckman Development THE BECKMAN Spectrophotometer". News Edition of the American Chemical Society. American Chemical Society. September 25, 1941. p. NA.
  38. ^ Drees, Julia C.; Wu, Alan H. B. (2013). "Chapter 5: Analytic techniques" (PDF). In Bishop, Michael L.; Fody, Edward P.; Schoeff, Larry E. (eds.). Clinical chemistry : principles, techniques, and correlations. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. pp. 131–134. ISBN 978-1-4511-1869-8. Retrieved 10 September 2016.
  39. ^ a b c d Pillsbury, Dale (November 2011). "Too Bad Indy – You Were Born Too Early (Or Perhaps Arnold Beckman was Born Too Late)" (PDF). The Alembic. 38 (3): 6. Retrieved 29 August 2016. conventional analysis for vitamin A content required analyzing the bone structure of the tails of rats fed oil for 21 days, while the Beckman DU with its UV capability was able to give a much more precise measurement of vitamin A content in just a few minutes.
  40. ^ Harrison, George R.; Lord, Richard C.; Loofbourow, John R. (1948). Practical spectroscopy. New York: Prentice-Hall. pp. 400–402. Retrieved 9 September 2016.
  41. ^ a b "Beckman DU Spectrophotometer". National Museum of American History. Retrieved 6 March 2014.
  42. ^ a b "In Memoriam: Arnold O. Beckman (1900–2004)". News and Views. 4 (18). May 24, 2004. Retrieved 10 March 2016. The spectrophotometer improved biological assays from a process that took weeks and achieved 25 percent accuracy to one that took minutes and achieved 99.9 percent precision. {{cite journal}}: Unknown parameter |agency= ignored (help)
  43. ^ a b . Massachusetts Institute of Technology. Archived from the original on 6 September 2015. Retrieved 6 March 2014. This device forever simplified and streamlined chemical analysis, by allowing researchers to perform a 99.9% accurate quantitative measurement of a substance within minutes, as opposed to the weeks required previously for results of only 25% accuracy.
  44. ^ Royer, G. L.; Lawrence, H. C.; Kodama, S. P.; Warren, C. W. (April 1955). "Manual and Continuous Recording Attachments for Beckman Model DU Spectrophotometer". Analytical Chemistry. 27 (4): 501–506. doi:10.1021/ac60100a005.
  45. ^ Browne, Malcolm W. (November 10, 1987). "After Decades, Inventor's Work Is Still Felt in the Laboratory". The New York Times. Retrieved 9 March 2016.
  46. ^ Brown, Theodore L. (2009). Bridging divides : the origins of the Beckman Institute at Illinois. Urbana: University of Illinois. ISBN 978-0-252-03484-8.
  47. ^ "Our History". Beckman Coulter. Retrieved 6 September 2016.[permanent dead link]
  48. ^ Mark, Andrew (September 21, 2007). . Laboratory News. Archived from the original on 6 March 2014. Retrieved 6 March 2014.
  49. ^ Avampato, J.E.; Eaton, H.D. (August 1953). "Comparison of Methods for the Estimation of Vitamin A in Calf Plasma". Journal of Dairy Science. 36 (8): 783–793. doi:10.3168/jds.S0022-0302(53)91563-X. Retrieved 10 September 2016.
  50. ^ Sebrell, W. H.; Harris, Robert S. (1954). The Vitamins: Chemistry, Physiology, Pathology. New York: Academic Press. p. 89. ISBN 9781483222028. Retrieved 14 March 2016. ... nowadays the preference is generally for the much easier and more precise measurement by a spectrophotometer, e.g. of the Beckman DU type ...
  51. ^ Cartwright, Anthony C. (June 28, 2015). The British Pharmacopoeia, 1864 to 2014: Medicines, International Standards and the State. Farnham, Surrey & Burlington, Vermont: Ashgate Publishing, Ltd. ISBN 978-1-4724-2032-9. Retrieved 17 March 2016. In 1941, they started selling the Beckman DU spectrophotometer which was a workhorse in countless laboratories for decades.
  52. ^ a b c d Friedkin, Morris E. (1995). "Growing up in the golden era of intermediary metabolism". Protein Science. 4 (2): 311–325. doi:10.1002/pro.5560040218. PMC 2143065. PMID 7757020. The research was part of a national mission: to make penicillin available to all of our forces and by secrecy to prevent its use by Germany and Japan. Within a year, 17 drug companies were working on penicillin.
  53. ^ a b Sneader, Walter (2005). Drug Discovery: A History. Chichester: John Wiley. p. 294. ISBN 978-0-470-35929-7. The drug exceeded all expectations, but the public were not told since penicillin was classified as a US military secret.
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  56. ^ Kelly, Norman V. (April 20, 2013). "We called her 'Moldy Mary'". Peoria Historian. Retrieved 14 March 2016.
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External links edit

  • Jaehnig, Kenton G. Finding Aid to the Beckman historical collection, 1911–2011 (bulk 1934–2004). OCLC 899243886. Retrieved 6 February 2018. Links on landing page go to full documents. {{cite book}}: |website= ignored (help)

January 01, 1970
spectrophotometer, beckman, introduced, 1941, first, commercially, viable, scientific, instrument, measuring, amount, ultraviolet, light, absorbed, substance, this, model, spectrophotometer, enabled, scientists, easily, examine, identify, given, substance, bas. The DU spectrophotometer or Beckman DU introduced in 1941 was the first commercially viable scientific instrument for measuring the amount of ultraviolet light absorbed by a substance This model of spectrophotometer enabled scientists to easily examine and identify a given substance based on its absorption spectrum the pattern of light absorbed at different wavelengths Arnold O Beckman s National Technical Laboratories later Beckman Instruments developed three in house prototype models A B C and one limited distribution model D before moving to full commercial production with the DU Approximately 30 000 DU spectrophotometers were manufactured and sold between 1941 and 1976 DU Spectrophotometer National Technical Laboratories 1947 Sometimes referred to as a UV Vis spectrophotometer because it measured both the ultraviolet UV and visible spectra the DU spectrophotometer is credited as being a truly revolutionary technology It yielded more accurate results than previous methods for determining the chemical composition of a complex substance and substantially reduced the time needed for an accurate analysis from weeks or hours to minutes The Beckman DU was essential to several critical secret research projects during World War II including the development of penicillin and synthetic rubber Contents 1 Background 2 Development 2 1 Model A prototype 2 2 Model B prototype 2 3 Model C prototype 2 4 Model D limited production 2 5 Model DU 3 Design 4 Use 5 Impact 5 1 Vitamins 5 2 Penicillin 5 3 Hydrocarbons 5 4 Enzyme assays and DNA research 5 5 Biotechnology 6 Later models 7 References 8 External linksBackground editBefore the development of the DU spectrophotometer analysis of a test sample to determine its components was a long costly and often inaccurate process A classical wet laboratory contained a wide variety of complicated apparatus 1 Test samples were run through a series of awkward and time consuming qualitative processes to separate out and identify their components Determining quantitative concentrations of those components in the sample involved further steps Processes could involve techniques for chemical reactions precipitations filtrations and dissolutions 2 150 3 Determination of the concentrations of known impurities in a known inorganic substance such as molten iron could be done in under thirty minutes 2 26 The determination of complex organic structures such as chlorophyll using wet and dry methods could take decades 4 59 60 Spectroscopic methods for observing the absorption of electromagnetic radiation in the visible spectrum were known as early as the 1860s 4 65 5 5 Scientists had observed that light traveling through a medium would be absorbed at different wavelengths depending on the matter composition of the medium involved A white light source would emit light at multiple wavelengths over a range of frequencies A prism could be used to separate a light source into specific wavelengths Shining the light through a sample of a material would cause some wavelengths of light to be absorbed while others would be unaffected and continue to be transmitted Wavelengths in the resulting absorption spectrum would differ depending upon the atomic and molecular composition if the material involved 6 7 8 Spectroscopic methods were predominantly used by physicists and astrophysicists Spectroscopic techniques were rarely taught in chemistry classes and were unfamiliar to most practicing chemists Beginning around 1904 Frank Twyman of the London instrument making firm Adam Hilger Ltd tried to develop spectroscopic instruments for chemists but his customer base was consistently made up of physicists rather than chemists 9 113 118 By the 1930s he had developed a niche market in metallurgy where his instruments were well adapted to the types of problems that chemists were solving 9 124 By the 1940s both academic and industrial chemists were becoming increasingly interested in problems involving the composition and detection of biological molecules Biological molecules including proteins and nucleic acids absorb light energy in both the ultraviolet and visible range 10 The spectrum of visible light was not broad enough to enable scientists to examine substances such as vitamin A 11 Accurate characterization of complex samples particularly of biological materials would require the accurate reading of absorption frequencies in the ultraviolet and infrared IR sections of the spectrum in addition to visible light Existing instruments such as the Cenco Spectrophotelometer and the Coleman Model DM Spectrophotometer could not be effectively used to examine wavelengths in the ultraviolet range 11 12 The array of equipment needed to measure light energy reaching beyond the visible spectrum towards the ultraviolet could cost a laboratory as much as 3 000 a huge amount in 1940 2 149 Repeated readings of a sample were taken to produce photographic plates showing the absorption spectrum of a material at different wavelengths An experienced human could compare these to the known images to identify a match Then information from the plates had to be combined to create a graph showing the spectrum as a whole Ultimately the accuracy of such approaches was dependent on accurate consistent development of the photographic plates and on human visual acuity and practice in reading the wavelengths 2 150 151 Development editThe DU was developed at National Technical Laboratories later Beckman Instruments under the direction of Arnold Orville Beckman an American chemist and inventor 13 14 Beginning in 1940 National Technical Laboratories developed three in house prototype models A B C and one limited distribution model D before moving to full commercial production with the DU in 1941 5 6 Beckman s research team was led by Howard Cary who went on to co found Applied Physics Corporation later Cary Instruments which became one of Beckman Instruments strongest competitors 15 Other scientists included Roland Hawes and Kenyon George 16 Coleman Instruments had recently coupled a pH meter with an optical phototube unit to examine the visual spectrum the Coleman Model DM 10 Beckman had already developed a successful pH meter for measuring acidity of solutions his company s breakthrough product Seeing the potential to build upon their existing expertise Beckman made it a goal to create an easy to use integrated instrument which would both register and report specific wavelengths extending into the ultraviolet range Rather than depending on development of photographic plates or a human observer s visual ability to detect wavelengths in the absorption spectrum phototubes would be used to register and report the specific wavelengths that were detected This had the potential to increase the instrument s accuracy and reliability as well as its speed and ease of use 2 149 151 Model A prototype edit The first prototype Beckman spectrophotometer the Model A was created at National Technologies Laboratories in 1940 It used a tungsten light source with a glass Fery prism as a monochromator 17 16 18 Tungsten was used for incandescent light filaments because it was strong withstood heat and emitted a steady light 19 Types of light sources differed in the range of wavelengths of light that they emitted Tungsten lamps were useful in the visible light range but gave poor coverage in the ultraviolet range However they had the advantage of being readily available because they were used as automobile headlamps 17 17 An external amplifier from the Beckman pH meter and a vacuum tube photocell were used to detect wavelengths 17 16 Model B prototype edit nbsp Optical quality quartz crystals It was quickly realized that a glass dispersive prism was not suitable for use in the ultraviolet spectrum 2 153 17 16 Glass absorbed electromagnetic radiation below 400 millimicrons rather than dispersing it 20 In the Model B a quartz prism was substituted for the earlier glass 2 153 17 16 A tangent bar mechanism was used to adjust the monochromator The mechanism was highly sensitive and required a skilled operator 17 16 Only two Model B prototypes were made One was sold in February 1941 to the University of California Chemistry department in Los Angeles 2 153 The Model B prototype should be distinguished from a later production model of spectrophotometer that was also referred to as the Model B The production Model B was introduced in 1949 as a less expensive simple to use alternative to the Beckman DU 21 It used a glass Fery prism as a chromator and operated in a narrower range roughly from 320 millimicrons to 950 millimicrons and 5 to 20 A 22 183 184 23 24 25 Model C prototype edit Three Model C instruments were then built improving the instrument s wavelength resolution The Model B s rotary cell compartment was replaced with a linear sample chamber The tangent bar mechanism was replaced by a scroll drive mechanism 17 16 which could be more precisely controlled to reset the quartz prism and select the desired wavelength 10 With this new mechanism results could be more easily and reliably obtained without requiring a highly skilled operator This set the pattern for all of Beckman s later quartz prism instruments 17 16 Although only three Model B prototypes were built all were sold one to Caltech and the other two to companies in the food industry 2 153 Model D limited production edit nbsp Quartz photoelectric spectrophotometer Cary amp Beckman 1941 26 687 The A B and C prototype models all coupled an external Beckman pH meter to the optical component to obtain readouts In developing the Model D Beckman took the direct coupled amplifier circuit from the pH meter and combined the optical and electronic components in a single housing making it more economical 10 Moving from a prototype to production of the Model D involved challenges Beckman originally approached Bausch and Lomb about making quartz prisms for the spectrophotometer When they turned down the opportunity National Technical Laboratories designed its own optical system including both a control mechanism and a quartz prism Large high optical quality quartz suitable for creating prisms was difficult to obtain It came from Brazil and was in demand for wartime radio oscillators Beckman had to obtain a wartime priority listing for the spectrophotometer to get access to suitable quartz supplies 17 17 Beckman had previously attempted to find a source of reliable hydrogen lamps seeking better sensitivity to wavelengths in the ultraviolet range than was possible with tungsten As described in July 1941 the Beckman spectrophotometer could use a hot cathode hydrogen discharge tube or a tungsten light source interchangeably 26 684 685 However Beckman was still unsatisfied with the available hydrogen lamps National Technical Laboratories designed its own hydrogen lamp an anode enclosed in a thin blown glass window 17 17 By December 1941 the in house design was being used in production of the Model D 2 154 155 The instrument s design also required a more sensitive phototube than was commercially available at that time Beckman was able to obtain small batches of an experimental phototube from RCA for the first Model D instruments 17 17 The Model D spectrophotometer using the experimental RCA phototube was shown at MIT s Summer Conference on Spectroscopy in July 1941 The paper that Cary and Beckman presented there was published in the Journal of the Optical Society of America In it Cary and Beckman compared designs for a modified self collimating quartz Fery prism a mirror collimated quartz Littrow prism and various gratings 26 683 The Littrow prism was a half prism which had a mirrored back face so that the light went through the front face twice 18 27 31 34 Use of a tungsten light source with the quartz Littrow prism as a monochromator was reported to minimize light scattering within the instrument 26 686 The Model D was the first model to enter actual production A small number of Model D instruments were sold beginning in July 1941 before it was superseded by the DU 2 153 155 17 17 18 Model DU edit nbsp Disassembled absorption cell and photo tube compartment Cary amp Beckman 1941 26 687 When RCA could not meet Beckman s demand for experimental phototubes National Technical Laboratories again had to design its own components in house 17 18 They developed a pair of phototubes sensitive to the red and blue areas of the spectrum capable of amplifying the signals they received 28 230 With the incorporation of Beckman s UV sensitive phototubes the Model D became the Model DU UV Vis spectrophotometer 17 18 Its designation as a UV Vis spectrophotometer indicates its ability to measure light in both the visible and ultraviolet spectra 29 The DU was the first commercially viable scientific instrument for measuring the amount of ultraviolet light absorbed by a substance 2 148 5 10 As he had done with the pH meter Beckman had replaced an array of complicated equipment with a single easy to use instrument One of the first fully integrated instruments 17 11 or black boxes used in modern chemical laboratories 30 it sold for 723 in 1941 12 It is generally assumed that the DU in the name was a combination of D for the Model D on which it was based and U for the ultraviolet spectrum However it has been suggested that DU may also reference Beckman s fraternity at the University of Illinois Delta Upsilon whose members were called DU s 31 A publication in the scholarly literature compared the optical quality of the DU to the Cary 14 Spectrophotometer another leading UV Vis spectrophotometer of the time 32 Design edit nbsp Model DU spectrophotometer exploded view Beckman manual 1954 From 1941 until 1976 when it was discontinued the Model DU spectrophotometer was built upon what was essentially the same design 12 It was a single beam instrument 16 11 33 The DU spectrophotometers used a quartz prism to separate light from a lamp into its absorption spectrum and a phototube to electrically measure the light energy across the spectrum This allowed the user to plot the light absorption spectrum of a substance to obtain a standardized fingerprint characteristic of a compound 2 151 34 35 All modern UV Vis spectrophotometer are built on the same basic principles as the DU spectrophotometer 29 nbsp Diagram of Model DU optical system Beckman manual 1954 Light from the tungsten lamp is focused by the condensing mirror and directed in a beam to the diagonal slit entrance mirror The entrance mirror deflects the light through the entrance slit and into the monochromator to the collimating mirror Light falling on the collimating mirror is rendered parallel and reflected to the quartz prism where it undergoes refraction The back surface of the prism is aluminized so that light refracted at the first surface is reflected back through the prism undergoing further refraction as it emerges from the prism The desired wavelength of light is selected by rotating the Wavelength Selector which adjusts the position of the prism The spectrum is directed back to the collimating mirror which centers the chosen wavelength on the exit slit and sample Light passing through the sample strikes the phototube causing a current gain The current gain is amplified and registered on the null meter Model DU Optical System 36 3 Although the default light source for the instrument was tungsten a hydrogen or mercury lamp could be substituted depending on the optimal range of measurement for which the instrument was to be used 36 3 The tungsten lamp was suitable for transmittance of wavelengths between 320 and 1000 millimicrons the hydrogen lamp for 220 to 320 millimicrons and the mercury lamp for checking the calibration of the spectrophotometer 36 6 nbsp Minimum spectral band widths Cary amp Beckman 1941 As advertised in the 1941 News Edition of the American Chemical Society the Beckman Spectrophotometer used an autocollimating quartz crystal prism for a monochromator capable of covering a range from the ultraviolet 200 millimicrons to the infrared 2000 millimicrons with a nominal bandwidth of 2 millimicrons or less for most of its spectral range The slit mechanism was continuously adjustable from 01 to 2 0 mm and claimed to have less than 1 10 of stray light over most of the spectral range It featured an easy to read wavelength scale simultaneously reporting Transmission and Density information 37 The sample holder held up to 4 cells 36 3 37 Cells could be moved into the light path via an external control allowing the user to take multiple readings without opening the cell compartment 36 3 As described in the DU s manual absorbance measurements of a sample were made in comparison to a blank or standard a solution identical in composition with the sample except that the absorbing material being measured is absent 36 24 The standard could be a cell filled with a solvent such as distilled water 36 24 or a prepared solvent of a known concentration 27 30 31 At each wavelength two measurements are made with the sample and with the standard in the light beam This enables the ratio transmittance to be obtained For quantitative measurements transmittance is converted to absorbance which is proportional to the solute concentration according to Beer s law This makes possible the quantitative determination of the amount of a substance in solution 38 The user could also switch between phototubes without removing the sample holder A 1941 advertisement indicates that three types of phototubes were available with maximum sensitivity to red blue and ultraviolet light ranges 37 The 1954 DU spectrophotometer differs in that it claims to be useful from 200 to 1000 millimicrons 36 2 and does not mention the ultraviolet phototube 36 3 The wavelength selector however still ranged from 200 to 2000 millimicrons 36 4 and an Ultraviolet accessory set was available 36 25 This shift away from using the DU for infrared measurement is understandable since by 1954 Beckman Instruments was marketing a separate infrared spectrophotometer Beckman developed the IR 1 infrared spectrophotometer during World War II and redesigned it as the IR 4 between 1953 and 1956 2 165 39 6 7 Use edit nbsp Beckman DU spectrophotometer in use The Beckman spectrophotometer was the first easy to use single instrument containing both the optical and electronic components needed for ultraviolet absorption spectrophotometry within a single housing 2 153 The user could insert a cell tray with standard and sample cells dial up the desired wavelength of light confirm that the instrument was properly set by measuring the standard and then measure the amount of absorption of the sample reading the frequency from a simple meter 40 A series of readings at different wavelengths could be taken without disturbing the sample 41 The DU spectrophotometer s manual scanning method was extremely fast reducing analysis times from weeks or hours to minutes 39 6 42 43 It was accurate in both the visible and ultraviolet ranges 29 Working in both the ultraviolet and the visible regions of the spectrum the model DU produced accurate absorption spectra which could be obtained with relative ease and accurately replicated 41 The National Bureau of Standards ran tests to certify that the DU s results were accurate and repeatable and recommended its use 2 156 Other advantages included its high resolution and the minimization of stray light in the ultraviolet region 12 Although it was not cheap its initial price of 723 12 made it available to the average laboratory 44 501 In comparison in 1943 the GE Hardy Spectrophotometer cost 6 400 39 6 Practical and reliable the DU rapidly established itself as a standard for laboratory equipment 35 141 Impact edit nbsp World War II poster encouraged researchers to Give this job Everything You ve got Credited with having brought about a breakthrough in optical spectroscopy 5 10 the Beckman DU has been identified as an indispensable tool for chemistry 2 207 and the Model T of laboratory instruments 12 Approximately 30 000 DU spectrophotometers were manufactured and sold between 1941 and 1976 5 11 45 The DU enabled researchers to perform easier analysis of substances by quickly taking measurements at more than one wavelength to produce an absorption spectrum describing the complete substance For example the standard method of analysis of the vitamin A content of shark liver oil before the introduction of the DU spectrophotometer involved feeding the oil to rats for 21 days then cutting off the rats tails and examining their bone structure With the DU s UV technology vitamin A content of shark liver oil could be determined directly in a matter of minutes 39 6 The Scripps Research Institute and the Massachusetts Institute of Technology credit the DU with improving both accuracy and speed of chemical analysis MIT states This device forever simplified and streamlined chemical analysis by allowing researchers to perform a 99 9 accurate quantitative measurement of a substance within minutes as opposed to the weeks required previously for results of only 25 accuracy 42 43 Inorganic chemist and philosopher of science Theodore L Brown states that it revolutionized the measurement of light signals from samples 46 2 Nobel laureate Bruce Merrifield is quoted as calling the DU spectrophotometer probably the most important instrument ever developed towards the advancement of bioscience 12 Historian of science Peter J T Morris identifies the introduction of the DU and other scientific instruments in the 1940s as the beginning of a Kuhnian revolution 4 80 For the Beckman company the DU was one of three foundational inventions the pH meter the DU spectrophotometer and the helipot potentiometer that established the company on a secure financial basis and enabled it to expand 47 Vitamins edit Development of the spectrophotometer had direct relevance to World War II and the American war effort The role of vitamins in health was of significant concern as scientists wanted to identify Vitamin A rich foods to keep soldiers healthy Previous methods of assessing Vitamin A levels involved feeding rats a food for several weeks and then performing a biopsy to estimate ingested Vitamin A levels In contrast examining a food sample with a DU spectrophotometer yielded better results in a matter of minutes 48 The DU spectrophotometer could be used to study both vitamin A and its precursor carotenoids 49 and rapidly became the preferred method of spectrophotometric analysis 11 50 51 Penicillin edit The DU spectrophotometer was also an important tool for scientists studying and producing the new wonder drug penicillin 10 The development of penicillin was a secret national mission involving 17 drug companies with the goal of providing penicillin to all U S Forces engaged in World War II 52 312 53 It was known that penicillin was more effective than sulfa drugs 52 312 and that its use reduced mortality severity of long term wound trauma and recovery time 2 158 However its structure was not understood isolation procedures used to create pure cultures were primitive and production using known surface culture techniques was slow 52 312 At Northern Regional Research Laboratory in Peoria Illinois researchers collected and examined more than 2 000 specimens of molds as well as other microorganisms 54 An extensive research team included Robert Coghill Norman Heatley Andrew Moyer Mary Hunt 55 56 57 Frank H Stodola and Morris E Friedkin Friedkin recalls that an early model of the Beckman DU spectrophotometer was used by the penicillin researchers in Peoria 52 316 The Peoria lab was successful in isolating and commercially producing superior strains of the mold which were 200 times more effective than the original forms discovered by Alexander Fleming 55 By the end of the war American pharmaceutical companies were producing 650 billion units of penicillin each month 55 Much of the work done in this area during World War II was kept secret until after the war 2 158 53 Hydrocarbons edit The DU spectrophotometer was also used for critical analysis of hydrocarbons A number of hydrocarbons were of interest to the war effort Toluene a hydrocarbon in crude oil was used in production of TNT for military use 2 158 159 17 19 Benzene and butadienes were used in the production of synthetic rubber 58 Rubber used in tires for jeeps airplanes and tanks was in critically short supply because the United States was cut off from foreign supplies of natural rubber 2 158 159 The Office of Rubber Reserve organized researchers at universities and in industry to secretly work on the problem 59 The demand for synthetic rubber caused Beckman Instruments to develop infrared spectrophotometers Infrared spectrophotometers were better suited than UV Vis spectrophotometers to the analysis of C4 hydrocarbons particularly for applications in petroleum refining and gasoline production 2 159 4 17 Enzyme assays and DNA research edit Gerty Cori and her husband Carl Ferdinand Cori won the Nobel Prize in Physiology or Medicine in 1947 in recognition of their work on enzymes They made several discoveries critical to understanding carbohydrate metabolism including the isolation and discovery of the Cori ester glucose 1 phosphate and the understanding of the Cori cycle They determined that the enzyme phosphorylase catalyzes formation of glucose 1 phosphate which is the beginning and ending step in the conversions of glycogen into glucose and blood glucose to glycogen Gerty Cori was also the first to show that a defect in an enzyme can be the cause of a human genetic disease 60 The Beckman DU spectrophotometer was used in the Cori laboratory to calculate enzyme concentrations including phosphorylase 61 Another researcher who spent six months in 1947 at the Cori laboratory the most vibrant place in biochemistry at that time was Arthur Kornberg 62 Kornberg was already familiar with the DU spectrophotometer which he had used at Severo Ochoa s laboratory at New York University The new and scarce Beckman DU loaned to Ochoa by the American Philosophical Society was highly prized and in constant use Kornberg used it to purify aconitase an enzyme in the citric acid cycle 62 63 The enzyme could be assayed in a few minutes by coupling it to isocitrate dehydrogenase and in measuring the NADH formed using the Beckman DU spectrophotometer an instrument that transformed biochemistry 63 113 Kornberg and Bernard L Horecker used the Beckman DU spectrophotometer for enzyme assays measuring NADH and NADPH They determined their extinction coefficients establishing a basis for quantitative measurements in reactions involving nucleotides This work became one of the most cited papers in biochemistry 63 115 Kornberg went on to study nucleotides in DNA synthesis isolating the first DNA polymerizing enzyme DNA polymerase I in 1956 and receiving the Nobel Prize in Physiology or Medicine with Severo Ochoa in 1959 64 The bases of DNA absorbed ultraviolet light near 260 nm 10 Inspired by the work of Oswald Avery 65 on DNA Erwin Chargaff used a DU spectrophotometer in the 1940s in measuring the relative concentrations of bases in DNA 66 260 290 302 Based on this research he formulated Chargaff s rules 67 In the first complete quantitative analysis of DNA he reported the near equal correspondence of pairs of bases in DNA with the number of guanine units equaling the number of cytosine units and the number of adenine units equaling the number of thymine units He further demonstrated that the relative amounts of guanine cytosine adenine and thymine varied between species In 1952 Chargaff met Francis Crick and James D Watson discussing his findings with them Watson and Crick built upon his ideas in their determination of the structure of DNA 67 Biotechnology edit Ultraviolet spectroscopy has wide applicability in molecular biology particularly the study of photosynthesis 68 It has been used to study a wide variety of flowering plants and ferns 69 by researchers in departments of biology plant physiology and agriculture science as well as molecular genetics 70 Particularly useful in detecting conjugated double bonds the new technology made it possible for researchers like Ralph Holman and George O Burr to study dietary fats work that had significant implications for human diet 71 The DU spectrophotometer was also used in the study of steroids 72 73 by researchers like Alejandro Zaffaroni 74 who helped to develop the birth control pill the nicotine patch and corticosteroids 75 Later models edit nbsp Beckman Model DK1 Ultraviolet Spectrophotometer The Beckman team eventually developed additional models as well as a number of accessories or attachments which could be used to modify the DU for different types of work One of the first accessories was a flame attachment with a more powerful photo multiplier to enable the user to examine flames such as potassium sodium and cesium 1947 16 11 28 230 In the 1950s Beckman Instruments developed the DR and the DK both of which were double beam ultraviolet spectrophotometers The DK was named for Wilbur I Kaye who developed it by modifying the DU to expand its range into the near infrared 16 He did the initial work while at Tennessee Eastman Kodak and later was hired by Beckman Instruments 76 The DKs introduced an automatic recording feature The DK 1 used a non linear scroll and the DK 2 used a linear scroll to automatically record the spectra 76 21 The DR incorporated a robot operator which would reset the knobs on the DU to complete a sequence of measurements at different wavelengths just like a human operator would to generate results for a full spectrum It used a linear shuttle with four positions and a superstructure to change the knobs It had a moving chart recorder to plot results with red green and black dots 16 The price of recording spectrophotometers was substantially higher than non recording machines 72 The DK was ten times faster than the DR but not quite as accurate 16 It used a photomultiplier which had introduced a source of error 76 21 The DK s speed made it preferred to the DR 16 Kaye eventually developed the DKU combining infrared and ultraviolet features in one instrument but it was more expensive than other models 76 The last DU spectrophotometer was produced on July 6 1976 77 By the 1980s computers were being incorporated into scientific instruments such as Bausch amp Lomb s Spectronic 2000 UV Vis spectrophotometer to improve data acquisition and provide instrument control 29 Specialized spectrophotometers designed for specific tasks now tend to be used rather than general all purpose machines like the DU 5 1 78 References edit Dulski Thomas R 1996 The Wet Lab A manual for the chemical analysis of metals Online Ausg ed West Conshohocken PA ASTM pp 11 14 ISBN 978 0 8031 2066 2 Retrieved 30 August 2016 a b c d e f g h i j k l m n o p q r s t u v Thackray Arnold Myers Jr Minor 2000 Arnold O Beckman one hundred years of excellence Philadelphia Pa Chemical Heritage Foundation ISBN 978 0 941901 23 9 Braun Robert Denton 2016 Chemical analysis Encyclopaedia Britannica Retrieved 30 August 2016 a b c d Morris Peter J T Travis Anthony S 2002 The role of physical instrumentation in structural organic chemistry in the twentieth century In Morris Peter J T ed From classical to modern chemistry the instrumental revolution Cambridge Royal Society of Chemistry pp 57 84 ISBN 978 0 85404 479 5 a b c d e f Schmidt Werner 2005 Introduction to Optical Spectroscopy PDF Optical spectroscopy in chemistry and life sciences Weinheim Wiley VCH pp 1 11 ISBN 978 3 527 29911 9 Retrieved 14 March 2016 Experiment 10 PDF MMSU Physics and Astronomy Department Retrieved 9 September 2016 Harris Daniel C Bertolucci Michael D 1989 Symmetry and spectroscopy an introduction to vibrational and electronic spectroscopy Reprint ed New York Dover Publications ISBN 978 0 486 66144 5 Hollas J Michael 2004 Modern spectroscopy Chichester J Wiley ISBN 978 0 470 84416 8 a b Bigg Charlotte 2002 Adam Hilger Ltd and the Development of Spectrochemical Analysis In Morris Peter J T ed From classical to modern chemistry the instrumental revolution Cambridge Royal Society of Chemistry pp 111 128 ISBN 978 0 85404 479 5 a b c d e f Smutzer Gregory October 15 2001 Spectrophotometers An Absorbing Tale The Scientist Retrieved 6 March 2014 The DU spectrophotometer was extensively used in the mass production of penicillin a b c Rosenfeld Louis 1997 Vitamine vitamin The early years of discovery Clinical Chemistry 43 4 680 685 doi 10 1093 clinchem 43 4 680 PMID 9105273 Archived from the original on 4 June 2016 Retrieved 17 March 2016 The DU met a need and was an immediate success It remained unsurpassed in its field for 35 years a b c d e f g Simoni Robert D Hill Robert L Vaughan Martha Tabor Herbert December 5 2003 A Classic Instrument The Beckman DU Spectrophotometer and Its Inventor Arnold O Beckman PDF Journal of Biological Chemistry 278 e1 79 doi 10 1016 S0021 9258 20 75750 9 Retrieved 15 December 2015 Gallwas Jerry 2004 People Arnold Orville Beckman 1900 2004 Analytical Chemistry 76 15 264 A 265 A doi 10 1021 ac041608j Jaehnig Kenton G Finding Aid to the Beckman historical collection 1911 2011 bulk 1934 2004 OCLC 899243886 Retrieved 6 February 2018 Links on landing page go to full documents a href Template Cite book html title Template Cite book cite book a website ignored help Martelle Scott April 2 2000 During a Remarkable Century of Research Innovation and Creative Tinkering Visionary Arnold Beckman Seldom Found a Problem He Couldn t Solve Until Now LA Times p 4 Archived from the original on August 29 2016 Retrieved 20 August 2016 a b c d e f g Brock David C Gallwas Gerald E 19 February 2002 Robert J Manning Transcript of an Interview Conducted by David C Brock and Gerald E Gallwas in Fullerton California on 19 February 2002 PDF Philadelphia PA Chemical Heritage Foundation a b c d e f g h i j k l m n o p Belser Karl Arnold Arnold Orville Beckman PDF Karl Belser Archived from the original PDF on 9 September 2016 Retrieved 10 March 2016 a b Stewart James E 1996 Optical principles and technology for engineers New York M Dekker p 202 ISBN 978 0 8247 9705 8 Retrieved 9 September 2016 Hunter Richard S Harold Richard W 1987 The measurement of appearance 2nd ed New York Wiley pp 246 248 ISBN 978 0 471 83006 1 Bisen Prakash S Sharma Anjana 2013 Introduction to instrumentation in life sciences Boca Raton FL CRC Press p 124 ISBN 978 1 4665 1240 5 Retrieved 8 September 2016 TheSpectrophotometers That Would Not Die PDF Caltech Retrieved 1 September 2016 Glover J 1956 Colorimetric Absportimetric and Fluorimetric Methods In Paech K Tracey M V eds Modern Methods of Plant Analysis Moderne Methoden der Pflanzenanalyse Berlin Springer Verlag pp 149 245 ISBN 9783642805301 Retrieved 30 August 2016 Phillips John P 1964 Spectra Structure Correlation New York amp London Academic Press p 6 ISBN 9781483263557 Retrieved 1 September 2016 Arthur H Thomas Company Analytical Chemistry 21 2 20A February 1949 doi 10 1021 ac60026a720 Beckman Instruments Analytical Chemistry 22 12 9A December 1950 doi 10 1021 ac60048a708 a b c d e Cary H H Beckman Arnold O 1941 A Quartz Photoelectric Spectrophotometer Journal of the Optical Society of America 31 11 682 689 Bibcode 1941JOSA 31 682C doi 10 1364 JOSA 31 000682 a b Robinson James W 1996 Atomic spectroscopy 2nd ed New York Dekker pp 30 33 ISBN 978 0 8247 9742 3 Retrieved 9 September 2016 a b Gardiner Kenneth 1956 Flame photometry In Berl Walter G ed Physical Methods in Chemical Analysis 3 ed New York Academic Press pp 219 290 ISBN 978 1 4832 5563 7 Retrieved 17 March 2016 a b c d Buie John July 13 2011 Evolution of UV Vis Spectrophotometers PDF Lab Manager pp 24 25 Archived from the original PDF on March 24 2016 Retrieved March 17 2016 Visible Proofs Forensic Views of the Body National Institutes of Health Retrieved 14 March 2016 Beckman Model DU Quartz Spectrophotometer Illinois Simulator Laboratory Retrieved 29 August 2016 Brode Wallace R Gould John H Whitney James E Wyman George M October 1953 A Comparative Survey of Spectrophotometers in the 210 760 mm Region Journal of the Optical Society of America 43 10 862 865 Bibcode 1953JOSA 43 862B doi 10 1364 JOSA 43 000862 Dulski Thomas R 1999 Trace elemental analysis of metals methods and techniques New York Marcel Dekker p 195 ISBN 978 0 8247 1985 2 Retrieved 31 August 2016 Jarnutowski R Ferraro J R Lankin D C 1992 Fifty years of commercial instrumentation in absorption spectroscopy part II Landmark instruments in UV vis Spectroscopy 7 22 24 26 a b Zweig Gunter 1976 Analytical Methods for Pesticides Plant Growth Regulators and Food Additives Principles Methods and General Applications New York Academic Press pp 141 143 ISBN 978 0 12 784301 8 Retrieved 9 September 2016 a b c d e f g h i j k Beckman Instruments Instruction Manual The Beckman Model DU Spectrophotometer and Accessories Fullerton CA Beckman Instruments Inc 1954 a b c Announcing an Important New Beckman Development THE BECKMAN Spectrophotometer News Edition of the American Chemical Society American Chemical Society September 25 1941 p NA Drees Julia C Wu Alan H B 2013 Chapter 5 Analytic techniques PDF In Bishop Michael L Fody Edward P Schoeff Larry E eds Clinical chemistry principles techniques and correlations Philadelphia Wolters Kluwer Health Lippincott Williams amp Wilkins pp 131 134 ISBN 978 1 4511 1869 8 Retrieved 10 September 2016 a b c d Pillsbury Dale November 2011 Too Bad Indy You Were Born Too Early Or Perhaps Arnold Beckman was Born Too Late PDF The Alembic 38 3 6 Retrieved 29 August 2016 conventional analysis for vitamin A content required analyzing the bone structure of the tails of rats fed oil for 21 days while the Beckman DU with its UV capability was able to give a much more precise measurement of vitamin A content in just a few minutes Harrison George R Lord Richard C Loofbourow John R 1948 Practical spectroscopy New York Prentice Hall pp 400 402 Retrieved 9 September 2016 a b Beckman DU Spectrophotometer National Museum of American History Retrieved 6 March 2014 a b In Memoriam Arnold O Beckman 1900 2004 News and Views 4 18 May 24 2004 Retrieved 10 March 2016 The spectrophotometer improved biological assays from a process that took weeks and achieved 25 percent accuracy to one that took minutes and achieved 99 9 percent precision a href Template Cite journal html title Template Cite journal cite journal a Unknown parameter agency ignored help a b Arnold O Beckman Massachusetts Institute of Technology Archived from the original on 6 September 2015 Retrieved 6 March 2014 This device forever simplified and streamlined chemical analysis by allowing researchers to perform a 99 9 accurate quantitative measurement of a substance within minutes as opposed to the weeks required previously for results of only 25 accuracy Royer G L Lawrence H C Kodama S P Warren C W April 1955 Manual and Continuous Recording Attachments for Beckman Model DU Spectrophotometer Analytical Chemistry 27 4 501 506 doi 10 1021 ac60100a005 Browne Malcolm W November 10 1987 After Decades Inventor s Work Is Still Felt in the Laboratory The New York Times Retrieved 9 March 2016 Brown Theodore L 2009 Bridging divides the origins of the Beckman Institute at Illinois Urbana University of Illinois ISBN 978 0 252 03484 8 Our History Beckman Coulter Retrieved 6 September 2016 permanent dead link Mark Andrew September 21 2007 Leading the way in chemical instrumentation Laboratory News Archived from the original on 6 March 2014 Retrieved 6 March 2014 Avampato J E Eaton H D August 1953 Comparison of Methods for the Estimation of Vitamin A in Calf Plasma Journal of Dairy Science 36 8 783 793 doi 10 3168 jds S0022 0302 53 91563 X Retrieved 10 September 2016 Sebrell W H Harris Robert S 1954 The Vitamins Chemistry Physiology Pathology New York Academic Press p 89 ISBN 9781483222028 Retrieved 14 March 2016 nowadays the preference is generally for the much easier and more precise measurement by a spectrophotometer e g of the Beckman DU type Cartwright Anthony C June 28 2015 The British Pharmacopoeia 1864 to 2014 Medicines International Standards and the State Farnham Surrey amp Burlington Vermont Ashgate Publishing Ltd ISBN 978 1 4724 2032 9 Retrieved 17 March 2016 In 1941 they started selling the Beckman DU spectrophotometer which was a workhorse in countless laboratories for decades a b c d Friedkin Morris E 1995 Growing up in the golden era of intermediary metabolism Protein Science 4 2 311 325 doi 10 1002 pro 5560040218 PMC 2143065 PMID 7757020 The research was part of a national mission to make penicillin available to all of our forces and by secrecy to prevent its use by Germany and Japan Within a year 17 drug companies were working on penicillin a b Sneader Walter 2005 Drug Discovery A History Chichester John Wiley p 294 ISBN 978 0 470 35929 7 The drug exceeded all expectations but the public were not told since penicillin was classified as a US military secret Klaus Abby Penicillin The Miracle Drug PDF Illinois Government Archived from the original PDF on 26 March 2016 Retrieved 14 March 2016 a b c Markel Howard 2013 09 27 The Real Story Behind Penicillin September 27 2013 PBS Newshour Retrieved 6 March 2014 Kelly Norman V April 20 2013 We called her Moldy Mary Peoria Historian Retrieved 14 March 2016 Our View Penicillin Another bit of area history deserving notice Journal Star October 7 2010 Retrieved 14 March 2016 Henglein F A Lang R F 1968 Chemical technology 1st English ed Oxford Pergamon Press ISBN 978 0 08 011848 2 Retrieved 15 March 2016 Beckman Infrared Spectrometer Chemical Heritage Foundation Archived from the original on February 4 2015 Retrieved 24 June 2013 Smeltzer Ronald K 2013 Extraordinary Women in Science amp Medicine Four Centuries of Achievement The Grolier Club Cori Carl F Illingworth Barbara July 15 1957 The prosthetic group of phosphorylase Proceedings of the National Academy of Sciences 43 7 547 552 Bibcode 1957PNAS 43 547C doi 10 1073 pnas 43 7 547 PMC 528497 PMID 16590054 a b Kornberg Arthur January 5 2001 Remembering Our Teachers The Journal of Biological Chemistry 276 1 3 11 doi 10 1016 S0021 9258 18 44198 1 PMID 11134064 Retrieved 17 March 2016 a b c Exton John H 2013 Arthur Kornberg Crucible of science the story of the Cori Laboratory New York Oxford University Press pp 112 122 ISBN 978 0 19 986107 1 Kresge Nicole Simoni Robert D Hill Robert L 2005 Arthur Kornberg s Discovery of DNA Polymerase I J Biol Chem 280 46 Retrieved 15 March 2016 Avery Oswald T MacLeod Colin M McCarty Maclyn February 1 1944 Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III Journal of Experimental Medicine 79 2 137 158 doi 10 1084 jem 79 2 137 PMC 2135445 PMID 19871359 Hunter Graeme K 2000 Vital forces the discovery of the molecular basis of life San Diego Academic Press ISBN 978 0 12 361810 8 Retrieved 17 March 2016 a b Board on Physics and Astronomy Division on Engineering and Physical Sciences 2006 Instrumentation for a better tomorrow proceedings of a symposium in honor of Arnold Beckman Washington D C National Academies Press p 14 ISBN 978 0 309 10116 5 Sandage Alan 2004 Centennial history of the Carnegie Institution of Washington Vol 4 Cambridge Cambridge University Press p 127 ISBN 978 0 521 83078 2 Ludlow C Joseph Wolf Frederick T April 1975 Photosynthesis and Respiration Rates of Ferns American Fern Journal 65 2 43 doi 10 2307 1546309 JSTOR 1546309 Sarkar Sahotra 2001 The philosophy and history of molecular biology new perspectives Dordrecht Kluwer Academic p 54 ISBN 978 1 4020 0249 6 Retrieved 17 March 2016 Holman Ralph T 1997 w3 and w6 Essential Fatty Acid Status in Human Health and Disease In Yehuda Shlomo Mostofsky David I eds Handbook of essential fatty acid biology biochemistry physiology and behavioral neurobiology Totowa N J Humana Press pp 139 182 ISBN 978 1 4757 2582 7 Retrieved 17 March 2016 a b Morris Peter J T Travis Anthony S 2003 Role of physical instrumentation in structural organic chemistry In Krige John Pestre Dominique eds Science in the twentieth century London Routledge p 725 ISBN 978 1 134 40686 9 Retrieved 14 March 2016 Weisbart Melvin 1973 Isolation and purification of hormones New York MSS Information Corp p 47 ISBN 978 0 8422 7107 3 Retrieved 17 March 2016 Kornberg Arthur 2002 The golden helix inside biotech ventures Sausalito Calif University Science Books p 62 ISBN 978 1 891389 19 1 Retrieved 17 March 2016 Pollack Andrew March 6 2014 Alejandro Zaffaroni Entrepreneur on Biotech Frontier Dies at 91 The New York Times Retrieved 17 March 2016 a b c d Thackray Arnold Gallwas Gerald E 27 February 2002 Wilbur I Kaye Transcript of an Interview Conducted by Arnold Thackray and Gerald E Gallwas at La Jolla California on 11 and 27 February 2002 PDF Philadelphia PA Chemical Heritage Foundation Beckman A O Gallaway W S Kaye W Ulrich W F March 1977 History of spectrophotometry at Beckman Instruments Inc Analytical Chemistry 49 3 280A 300A doi 10 1021 ac50011a001 Beck Shane February 2 1998 Across the Spectrum Instrumentation for UV Vis Spectrophotometry The Scientist Retrieved 9 September 2016 External links editJaehnig Kenton G Finding Aid to the Beckman historical collection 1911 2011 bulk 1934 2004 OCLC 899243886 Retrieved 6 February 2018 Links on landing page go to full documents a href Template Cite book html title Template Cite book cite book a website ignored help Retrieved from https en wikipedia org w index php title DU spectrophotometer amp oldid 1219545046, wikipedia, wiki, book, books, library,

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