Birth episode Birth of UV
In 1945, an ultraviolet-visible (UV-VIS) spectrophotometer was released in the United States. This instrument used a prism to disperse light, and a photoelectric tube to measure it. This was a ground-breaking analysis instrument, surpassing conventional colorimeters on the performance front, and became popular in the U.S.
The instrument was imported to Japan right after its release in the U.S. The quantitative accuracy of the imported UV-VIS spectrophotometer was significantly better than that of the colorimeters being used in Japan at that time. As a result, it became a major topic of discussion in the field of analytic chemistry, and at the same time, great hopes came to be held for a Japanese produced version. In response to this demand, engineers at Shimadzu proceeded with development through trial and error, using a sketch of the American UV-VIS spectrophotometer as a reference.
They were confronted with a problem however. While the American UV-VIS spectrophotometer used a hydrogen discharge tube as the light source for wavelengths of 400 nm or less in the ultraviolet region, no such tube was being produced in Japan at the time. Accordingly, Shimadzu called for cooperation on its affiliate, Japan Storage Battery Co., Ltd. (now GS Yuasa Corporation), which manufactured mercury lamps at the time, and was able to produce a hydrogen discharge tube rivaling those produced in the U.S.
While the UV-VIS spectrophotometers imported from the U.S. used a photoelectric tube as the detector,photomultiplier tubes, which provided several hundred times more sensitivity, came to be manufactured in the U.S. Accordingly, Shimadzu asked a Japanese photoelectric tube manufacturer to participate in collaborative research on photomultiplier tubes. Through the untiring efforts of this photoelectric tube manufacturer, a photomultiplier tube with performance rivaling American made models was then completed.
Through this sequence of events, Shimadzu's first UV-VIS spectrophotometer, the QB-50, was completed in 1952. This UV-VIS spectrophotometer used a crystal prism as the spectral element, and a photomultiplier tube as the detector for the first time in the world. Comparative tests with an American made UV-VIS spectrophotometer were performed by a university in Kyoto. The results showed that the QB-50 was quite sensitive at 220 nm, a wavelength that the American models could not measure, and that overall, the QB-50 compared favorably with the American models on the performance front. It met the needs of the time, sold well, and became Shimadzu's primary product.
The relationship between wavelength and color is shown in the following figure. Using a prism, light from a light source is dispersed into its respective wavelength components.
A wavelength is the length of 1 wave cycle, and is normally expressed with the symbol λ (lambda). In the UV-VIS region, nm (nanometer) units are used.
Relationship Between Wavelength and Color
Light is classified by wavelength. Light in the 380 nm to 780 nm range is called visible light, while wavelengths shorter than 380 nm are called ultraviolet light, and wavelengths longer than 780 nm are called infrared light. Visible light consists of a series of colors which, beginning from the shortest wavelength, range from violet, to blue, green, yellow, orange, and red, as can be confirmed from a rainbow.
Dispersion Using a Prism
A prism is a triangular prism-shaped piece of quartz or glass. When white light (light such as sunlight, consisting of a mix of various wavelength components) is incident on a prism, it will be refracted. The longer the wavelength, the smaller the angle of refraction for as the wavelength gets shorter, the angle of refraction gets bigger. As a result, the light is dispersed by color into red, yellow, green, blue, and purple, in that order.
|A photoelectric tube is a vacuum tube that uses the photoelectric effect to convert light energy into electrical energy. A photomultiplier tube adds current amplification functionality to the performance of a photoelectric tube. At present, photomultiplier tubes are used as the detector in UV-VIS spectrophotometers.||A colored liquid will absorb light at a specific wavelength. Using this phenomenon, a colorimeter measures light by utilizing a glass filter through which light at this specific wavelength passes. Various types of colorimeters have been developed. The photograph shows a Stammer-Engler colorimeter.||This is a type of discharge tube containing a minute quantity of hydrogen and is used as an ultraviolet light source. When such tubes contain deuterium, they are referred to as deuterium lamps. Deuterium lamps are used in UV-VIS spectrophotometers because they have strong irradiation intensity in comparison to light hydrogen.|
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