UV-Visible Analysis Applications

Ultraviolet/Visible Absorption Analysis

Photometric analyzers based on ultraviolet/visible (UV/Vis) absorption have found increasingly wide application in process indistries. The spectrum of interest here extends from 190 nm (near-UV wavelength) to 750 nm (deep red wavelength). There is lack of UV/Vis absorption by the atmospheric gases, water, aliphatic alcohols, ether and saturated aliphatic hydrocarbons. A strong UV-absorbing material could, of course, be sensitively and selectively analyzed in the presence of only these compounds. These are the simple UV/Vis analyzer applications; however such applications represent only a relatively small percentage of the thousands of analyses by ultraviolet and visible light absorption. Here are some specific applications:


  • Elemental Halogens, particularly chlorine, both in gaseous and liquid phases, are monitored by UV/Vis analyzers.
  • Oxidizing Agents have in general strong absorption bands. Besides the elemental halogens, examples are: sodium hypochlorite (NaOCl), chlorine dioxide (ClO2), hydrogen peroxide (H2O2), ozone (O3) and potassium permanganate (KmnO4). “Bleaching” steps can often be controlled by monitoring the oxidizing agent concentration.
  • Aromatic Compounds (benzene and its derivatives) are strong UV absorbers. Concentrations of aromatics in aliphatic hydrocarbons are monitored in very low concentrations. Aromatics, such as phenol (C6H6OH), in waste streams are continuously monitored with UV analyzers.
  • Sulfur Compounds often absorb strongly UV radiation. Low concentrations of hydrogen sulfide (H2S), carbonyl sulfide (COS), carbon disulfide (CS2) and sulfur dioxide (SO2) are monitored and controlled for safety, environmental compliance and process efficiency. The measurement of SO2 is probably the largest application of UV analyzers. Applications for monitoring low-ppm concentrations of H2S in hydrocarbon streams have been successful.
  • Inorganics salts of transition metals such as iron, copper, chromium, manganese and nickel are often strong absorbers of UV and/or visible radiation. Typical applications include measurement and control of ferrous ion concentration in steel pickling baths, cupric ions in nitric acid production and a number of metallic ions in plating baths.
  • Antibiotic Compounds have in general strong UV absorption. During their production, several process steps can be controlled by measurement ot the antibiotic concentration with UV analyzers.
  • Elemental Mercury the monitoring of elemental mercury vapor in the parts per billion range is actually an “atomic absorption” measurement.
  • Color measurement a multitude of products are graded on the basis of color; for many (lube oils, resins and solvents) color is the primary quality specification.


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