Spectrophotometric Analysis Applications
Spectrophotometric Analysis Applications

SpectrumSpectrophotometric Process Analysis


The fundamental principle of spectrophotometric analyzers is based on the fact that molecules in a process stream absorb light (more in general, electromagnetic energy) at specific frequencies. In a stream of known composition, it is possible to select one or more electromagnetic spectrum wavelengths that are unique to a component within the stream. An appropriate technique is then employed in which the absorption of energy at the specific frequency from the component is measured.

The Photodiode Array (PDA) detectors are able to detect multiple wavelengths, therefore enabling the analyzers to measure several stream components simultaneously. A common application of PDA detectors includes the measurement of several gases, such as H2O, CO2 and CO in process heater stacks (a measurement typically required as a part of the regulatory permit to operate the heater).

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:

Infrared Analysis Applications

Infrared (IR and NDIR) Absorption Analysis


Plots of electromagnetic energy absorption between 2 and 15 µm are known as infrared (IR) absorption spectra.

The number of IR absorption bands and the intensity of the absorption are directly related to the molecular structure. However there are molecular-specific absorptions exhibited within a series of compounds. For example, all organic compounds tend to exhibit IR absorption at about 3.4 µm, the group frequency of the ‘C-H’ bond vibration. Thus it may not be possible to discriminate among a mix of hydrocarbons at this wavelength and other absorptions bands should be utilized.

Process IR analyzers are dedicated quantitative analysis devices designed to monitor a single key component in a multicomponent stream. A wavelength is selected for which the component of interest (analyte) strongly absorbs infrared and background components are transparent. Process infrared analyzers do not use prisms or gratings and thus are defined as nondispersive infrared (NDIR) analyzers.

Near Infrared Analysis Applications

Near Infrared (NIR) Absorption Analysis


Near infrared includes electromagnetic wavelength range between 1100 and 2500 nm.

The NIR absorbance of a material depends primarily on its chemical composition.

NIR instruments typically make measurements by shining NIR light on the sample and measuring the received light at several wavelenghts. At least one wavelength is absorbed by the material being measured, and the others are chosen as appropriate to give the best stability and accuracy.

Water is the most common NIR measurement. This is because water is an extremely strong NIR absorber at its two absorption wavelengths of 1,940 and 1,430 nm. Also, no other common material absorb strongly at the 1,940 nm wavelength, making it easy for NIR techniques to distinguish water from the other constituents of the sample. 


Fourier Transform Analysis Applications

Fourier Transform Infrared (FTIR) Absorption Analysis


Fourier Transform Infrared analysis is based on the same physical measurement principle as nondispersive infrared analyzers (NDIR). The FTIR spectroscopy technique is able to determine the composition of complex mixtures of chemicals and is more accurate than NDIR analysis. This is possible because the absorption spectra of the materials are linear and additive. FTIR can make use of libraries of known spectra to interpret a complex spectrum.

Because of the broad range of applications for the Fourier Transform Infrared technique, the assistance of the BAGGI technical team is required in developing a specific application.

Typical applications can be:

  • Stack gas analyzers.
  • Polymer processing from input streams to final product.
  •  Gasoline composition.





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