Fourier Transform Near Infrared Spectroscopy

For practical reasons relating to the illumination sources and detectors, optical spectrometers cover some fixed range of wavelengths of light. The band of the electromagnetic spectrum with wavelengths just longer than the longest red wavelengths visible to the human eye is known as the near infrared (NIR). Although the exact borders of the NIR band are somewhat arbitrary, wavelengths from about 750 nm to 2500 nm are typically included. The NIR band separates visible light from the mid-infrared. While the mid-infrared is associated with many of the fundamental rotational and vibratory modes of molecules, the NIR region is sensitive to overtones of these fundamental modes and thus can be used for spectroscopy to identify molecules in a sample. One advantage of NIR over the mid-infrared is that NIR can generally penetrate further into a sample, making bulk measurements of materials more feasible

The general configuration of an NIR spectrometer is similar to many other forms of spectroscopy, with a light source, a place for the light to interact with the sample and a detector that analyzes the transmitted or reflected radiation. In Fourier Transform–NIR (FT-NIR), many different infrared sources are used, from simple incandescent lights to filtered laser sources. The common theme is that the sources provide multiple wavelengths of illumination. By modulating the mix of wavelengths impinging on the sample, the FT method can be used to determine the response of the sample at each individual wavelength, thus producing a spectrum. The use of the transform provides advantages in speed and signal-to-noise over other methods that may use dispersive filters or other methods to build up a spectrum. For detection, instruments commonly use a combination of two or more materials (e.g., both silicon and InGaAs) to provide the best response across the entire NIR range.

The majority of applications for NIR are in QC and inspection of incoming materials. While FT-NIR instruments generally have better performance specifications than lower-cost instruments, making them more suitable for research applications, the QC and inspection applications still predominate. The pharmaceutical industry is the largest individual source of demand for FT-NIR, with applications for the technique throughout the research and production suites. Systems with fiber optic probes are used to verify incoming materials, at-line and in-line systems are used to check the materials near or in the production line, while finished pharmaceutical products are also checked for QC. The next most common usage for FT-NIR is in the agriculture and food industry. Although lower-cost dispersive systems are very common in the food industry, FT-NIR systems have also gained popularity for similar applications in gauging the water, protein and fat content of food products. Polymers and plastic are also suitable for analysis by FT-NIR. Other sample types include chemicals, personal care products, paper and pulp, and other materials.

Three strong competitors dominate the market for FT-NIR. The market leader is Bruker, which offers several platforms for FT-NIR in benchtop, at-line and in-line configurations. PerkinElmer and Thermo Fisher Scientific round out the top three competitors in the market. Other competitors in FT-NIR include ABB, ARCoptix BÜCHI, AIT and Lumex . The total market demand for laboratory FT-NIR was about $125 million in 2016.

FT-NIR at a glance:

Leading FT-NIR Vendors

  • Bruker
  • PerkinElmer
  • Thermo Fisher Scientific

 Largest Markets

  • Pharmaceuticals
  • Agriculture and Food
  • Polymers and Plastics

FT-NIR Instrument Cost

  • $12,000–$80,000
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