DU spectrophotometer

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. 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. 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. 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.:150 Determination of the concentrations of known impurities in a known inorganic substance such as molten iron could be done in under thirty minutes.:26 The determination of complex organic structures such as chlorophyll using wet and dry methods could take decades. :59–60 Spectroscopic methods for observing the absorption of electromagnetic radiation in the visible spectrum were known as early as the 1860s.:65:5Scientists 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. 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.: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.: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. The spectrum of visible light was not broad enough to enable scientists to examine substances such as vitamin A. 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. 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.: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.:150–151 The DU was developed at National Technical Laboratories (later Beckman Instruments) under the direction of Arnold Orville Beckman, an American chemist and inventor. 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.: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. Other scientists included Roland Hawes and Kenyon George.