Near Infrared Spectroscopy (NIRS)

  • Introduction

    NIR spectroscopy is used for the compositional, functional and sensory analysis of ingredients, intermediates and final products. It is deployed in food and feed, agricultural, dairy, pharmaceutical, and chemical industries, which are under constant pressure to manufacture products that meet customer specifications while increasing plant production and profitability.

    NIR can be used for quantitative analysis (determination of substance concentrations), qualitative analysis (identification of raw materials, intermediate and finished products) and process control. It can provide information on moisture, protein, fat and starch content. NIR application vary in each industry and are custom designed to suit different companies and their specific products and needs.

  • The Science

    A NIR spectrometer measures overtones and combination tones of molecular vibrations in the infrared range, and especially, the asymmetric vibrations which are intensive in the near infrared range, i.e. stretch vibrations involving hydrogen bonds (e.g. C-H, O-H and N-H).

    How a spectrometer works

    The beam of light strikes the diffraction grating, which works like a prism and separates the light in its component wavelength. By means of InGaAs diode arrays it is possible to detect the whole wavelength range simultaneously. Near infrared (NIR) spectroscopy is based on the absorption of electromagnetic (EM) radiation at wavelengths in the range 780 to 2,500 nm. The light interacts with the sample and the detector measures its transmittance and absorbance. Transmittance refers to the amount of light that passes completely through the sample and strikes the detector. Absorbance is a measurement of light that is absorbed by the sample. The detector senses the light being transmitted through the sample and converts this information into a digital display.
    EM radiation is described by its frequency (f, typically in Hz), wavelength (λ) or photon energy (E). Wavelength is inversely proportional to frequency. Photon energy is directly proportional to frequency. When EM radiation interacts with atoms and molecules, its behavior depends on the amount of energy it carries. The energy of NIR radiation, e.g., has the power to cause overtones in molecular vibrations. The overtones of different molecule bonds absorb at specific frequencies that are characteristic of their structure.

  • Quantitative Analysis

    Quantitative Analysis

    Since several overtones overlap within one spectrum, NIR spectroscopy is manly used for quantitative analysis of known components instead for identification. By means of chemometrical tools, a correlation between reference spectra and reference analysis results is determined. The resulting calibration model is used for prediction of unknown samples.

    Benefits
    • Useful for analyzing all sorts of biological systems
    • Little or no sample preparation necessary
    • Non-destructive measurement method
    • Results emerge very fast within seconds
    • Universal application any molecule containing C­H, N­H, S­H or O­H bonds
    • Several analytical results can be predicted from the same NIR data
    • Simultaneous multi-component analysis without chemical or disposable costs
  • Examples of use
    • Solution for the agricultural sector to analyze crops, nutrition parameters of animal feed and raw materials for biofuel production. NIR generates key quality results for dry matter, protein, moisture, oil, particle size, ash, starch damage, water absorption and special chemical bonds.
    • Analyzes ingredients of food (meat and meat product, dairy, beverages, oils, baking products etc.) during process or through final product samples. Measurable parameters are moisture, protein, fat, free fatty acids, ethanol, density, solids, organic acids, carbohydrate profile, and other important constituents.
    • Suitable for chemists developing new compounds and as an online quality assurance tool for production. Measures the mixing efficacy or the internal structure of a solid sample, such as pills
    • Analyzes materials used in the non-food sector like bioenergy, pulp and paper, forestry, building, textiles
    • Method also works in presence of interfering substances, such as glass or plastic containers