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The Journal of the Royal Institute of Thailand Vol. 30 No. 4 Oct.-Dec. 2005 1132 Scientific Instrumentation in Research UV-vis Spectroscopy UV-vis spectroscopy probes the electronic transitions of molecules as they absorb light in the UV and visible regions of the electromagnetic spectrum. Any species with an extended system of alternating double and single bonds will absorb UV light, and anything with color absorbs visible light, making UV-vis spectroscopy applicable to a wide range of samples. A UV-vis spectrum of benzene is shown. The boom in ultraviolet spectroscopy began with vitamin A, but benzene is one of the most common chemicals that can be analyzed with UV-vis spectroscopy. In fact, a spectrum of benzene was included in the first article written about commercial UV-vis instruments. (Cary and Beckman, 1941) Today, UV-vis spectroscopy is one of the truly routine techniques in modern biochemistry, biology, and pharmaceutical research. UV-vis spectroscopy is used every day in thousands of labs around the world. Modern UV-vis instruments are quite different than when the DU was introduced in 1941, but they all operate on the same basic principles. The movie below explains the workings of the two most popular types of UV-vis spectrophotometers for research use today: the dual-beam and diode-array UV-vis spectrophotometers Nuclear magnetic resonance (NMR) Nuclear magnetic resonance (NMR) is one of the most powerful tools in a synthetic or structural chemist’s arsenal. By probing the magnetic properties of spin-active nuclei, chemists can learn more from an NMR spectrum than almost any other analytical technique. The application of NMR to chemistry is different from pH, UV-vis, and IR spectroscopy in that instrumentation was produced before applicable chemical problems were known. The Beckman Model G and Beckman DU were all instruments designed to answer specific questions asked by chemists of the time, but Varian began development of its line of NMR spectrometers well before commercially- viable applications were known. The result was an unusually short gestation period from the discovery of nuclear magnetic resonance to the introduction of the first widely successful instrument, the Varian A-60.