“The Spectrophotomer was my most impactful invention - it opened whole new avenues of research and discovery.”Dr. Arnold O. Beckman
What is a Spectrophotometer?
Chemicals can be identified by which wavelengths of light they absorb. A chemical absorbs light based on the number and strength of bonds that exist between the atoms that make up the chemical. A spectrophotometer is a device that shines light of specific wavelengths (a spectrum) through a sample, and then measures how much light passes through the sample using a photometer. By measuring each wavelength of light individually, a full adsorption spectrum can be graphed, which reveals the type and concentration of chemicals in a solution. Dr. Beckman's groundbreaking Ultraviolet Spectrophotometer uses this concept in a rugged and reliable bench-top instrument, where by simply turning a dial, an internal prism is rotated, exposing the sample to individual wavelengths of ultraviolet light.
Early Spectrophotmetry Systems, 1937-1940
In the mid 1930s, Dr. Beckman’s pH meter business at National Technical Laboratories was growing rapidly year over year, and they began expanding into other types of scientific instrumentation. There were other established instrument manufacturers, such as General Electric, Cenco, Coleman and Bausch & Lomb, who were selling Infrared (IR) and Visible light spectrophotometry systems. With these systems, chemists were starting to answer fundamental questions about chemical reactions, products and processes, but complex biological samples were still a mystery and did not have unique adsorption spectrum in the visible or IR light ranges.
Dr. Beckman realized that these systems needed to reach further into the Ultraviolet (UV) spectrum to analyze biological samples, but the UV light sources and compatible optics components for assembling such an instrument did not yet exist.
The Engineering Innovation
Dr. Arnold Beckman published a retrospective article about the evolution of the UV Spectrophometer at Beckman Instruments (formerly National Technical Laboratories) , some excerpts are below:
"In 1940, no one at National Technical Laboratories had any extensive experience in spectrophotometry. The fact was recognized, however, that the amplifier of the Beckman pH meter was well suited for use with vacuum-type phototubes. The company began a spectrophotometer development program in early 1940, and the responsibility for this program was assigned to H. H. Cary. Consulting assistance was sought from recognized optical experts, but World War II was under way and experts were hard to find. Roger Hayward, a professional architect 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.
The first instrument designed was a glass Fery prism instrument, but its performance was not considered suitable. A quartz prism Littrow design with a tangent-bar drive followed and was designated the Model Β. Of the two quartz Model Β instruments produced, one was sold to the Chemistry Department of the University of California of Los Angeles in February 1941, and the other is in the company’s historical museum. This instrument utilized a tangent-bar mechanism which provided a substantially linear wavelength scale. Unfortunately, the scale was too compressed, particularly in the ultraviolet region, and was replaced by a Model C with its innovative scroll drive, which was used in all subsequent Beckman quartz prism monochromators. Of the three Model C instruments produced, California Institute of Technology, Vita Foods Co., and Riverside Experiment Station each purchased one. The Caltech instrument was later returned to the company for its museum."
 Beckman, A.O., Gallaway, W. S., Kaye, W., and Ulrich, W. F. "History of Spectrophotometry at Beckman Instruments, Inc.". Analytical Chemistry, 49, pp 280A-300A (1977).
Impact of the Beckman DU Spectrophotometer
Vitamin A Analysis:
The first publication using a "Beckman DU" Spectrophotometer was in 1942 for analysis of the Vitamin A content in supplements being produced for troops in WWII theater . Before the Beckman DU, the assay to test for the concentration of Vitamin A in supplements involved:
- Feed rats a diet rich or poor in your supplement for 3 weeks
- Measure the length of tail growth
- Correlate amount of bone growth to Vitamin A concentration
This method was very slow, involved animal care, and relied on rat tail length to be a measure of Vitamin A intake.
After the Beckman DU, the assay to test for the concentration of Vitamin A in supplements was:
- Dissolve supplement in water
- Measure absorption spectra on Beckman DU
Impact: Reduce a 3-week experiment to 10 minutes, with greater accuracy and repeatability
 Morgareidge, K. "Influence of the Solvent on the Ultraviolet Absorption Maximum of Vitamin A". Industrial and Engineering Chemistry, 14, pp 700-702 (1942).
Rubber Manufacturing and Quality Control
During WWII, the US natural rubber supply was cut-off and the military began making synthetic rubber. However, the low yield of usable rubber could not meet the needs of the tire supplies to support the war effort.
To ensure quality rubber products, the concentration of butadiene in the source materials needed to be determined. Given the quality of the initial Beckman spectrophotometers, the US Office of Rubber Reserve asked Beckman Instruments to begin construction of IR Spectrophotometers based on the design used by Shell Development Company that could measure the chemical concentration of the source materials just before they were used in the rubber production.
By 1942, Beckman Model IR-1s were used at all synthetic rubber factories to analyze constituent materials during manufacture.
Impact: In-line quality control of manufacturing processes was born!
Nucleic Acid Analysis
In the mid-1940s, scientists were struggling to understand the chemical composition of the genetic information that was inherited, what we now know is DNA. Using a Beckman DU, Edwin Chargaff conducted experiments that discovered the adsorption spectrum of the four DNA amino acids, and that the abundance of adenine was the same as thymine, and guanine was the same as cytosine. This discovery led to the base pair theory of DNA assembly, which was essential to later solve the double-helix structure of DNA.
Impact: Fundamental knowledge of DNA which has led to countless medical discoveries
 Chargaff, E. "The Separation and Quantitative Estimation of Purines and Pyrimidines In Minute Amounts" J. Biol. Chem. 176, 703-714 (1948).
Production of DU Spectrophotometers, 1941-1976
From 1941 - 1976, Beckman Instruments would produce over 30,000 Beckman DU Spectrophotometers, with a variety of attachments for specialized chemical analysis. The manufacturing facility for these instruments in Fullerton, CA included all of the glass blowing, circuit board assembly, and quartz optics polishing for the construction of the components necessary for manufacture of the instruments. Below are some images of the facility in the 1950s as well as a TV program series called "Success Stories" which featured Beckman Instruments in 1955.
The company discontinued the DU Spectrophotometer as a stand-alone instrument in 1976.