Design DU spectrophotometer

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model du spectrophotometer - exploded view, beckman manual, 1954





from 1941 until 1976, when discontinued, model du spectrophotometer built upon same design. single beam instrument. du spectrophotometers used quartz prism separate light lamp absorption spectrum , phototube electrically measure light energy across spectrum. allowed user plot light absorption spectrum of substance obtain standardized fingerprint characteristic of compound. modern uv-vis spectrophotometer built on same basic principles du spectrophotometer.





diagram of model du optical system, beckman manual, 1954




light tungsten lamp focused condensing mirror , directed in beam diagonal slit entrance mirror. entrance mirror deflects light through entrance slit , monochromator collimating mirror. light falling on collimating mirror rendered parallel , reflected quartz prism undergoes refraction. surface of prism aluminized light refracted @ first surface reflected through prism, undergoing further refraction emerges prism. desired wavelength of light selected rotating wavelength selector adjusts position of prism. spectrum directed collimating mirror centers chosen wavelength on exit slit , sample. light passing through sample strikes phototube, causing current gain. current gain amplified , registered on null meter. model du optical system



although default light source instrument tungsten, hydrogen or mercury lamp substituted depending on optimal range of measurement instrument used. tungsten lamp suitable transmittance of wavelengths between 320 , 1000 millimicrons; hydrogen lamp 220 320 millimicrons, , mercury lamp checking calibration of spectrophotometer.





minimum spectral band widths, cary & beckman, 1941



as advertised in 1941 news edition of american chemical society, beckman spectrophotometer used autocollimating quartz crystal prism monochromator, capable of covering range ultraviolet (200 millimicrons) infrared (2000 millimicrons), nominal bandwidth of 2 millimicrons or less of spectral range. slit mechanism continuously adjustable .01 2.0 mm , claimed have less 1/10% of stray light on of spectral range. featured easy-to-read wavelength scale, simultaneously reporting % transmission , density information.


the sample holder held 4 cells. cells moved light path via external control, allowing user take multiple readings without opening cell compartment. described in du s manual, absorbance measurements of sample made in comparison blank, or standard, solution identical in composition sample except absorbing material being measured absent. standard cell filled solvent such distilled water or prepared solvent of known concentration. @ each wavelength 2 measurements made: sample , standard in light beam. enables ratio, transmittance, obtained. quantitative measurements transmittance converted absorbance proportional solute concentration according beer s law. makes possible quantitative determination of amount of substance in solution.


the user switch between phototubes without removing sample holder. 1941 advertisement indicates 3 types of phototubes available, maximum sensitivity red, blue , ultraviolet light ranges.


the 1954 du spectrophotometer differs in claims useful 200 1000 millimicrons, , not mention ultraviolet phototube. wavelength selector, however, still ranged 200 2000 millimicrons. , ultraviolet accessory set available. shift away using du infrared measurement understandable, since 1954 beckman instruments marketing separate infrared spectrophotometer. beckman developed ir-1 infrared spectrophotometer during world war ii, , redesigned ir-4 between 1953 , 1956.








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