Illuminating Spectra Part 6 - Spectral Range

In Illuminating Spectra part 5 we briefly mentioned the repetitive nature of NIR spectra. This means that there is always a degree of redundancy due to NH, OH and CH bonds absorbing at different wavelengths all at the same time. The consequence of this redundancy is that in many cases it becomes possible to extract similar information from different parts of the spectra.

This is one of the reasons behind the diversity of NIR machines in the market. There are many optical and digital differences between these instruments but one of the most noticeable differences is that they operate at different wavelength ranges.

NIR covers the span from 750 to 2500 nm but as you can see in the image below, some instrument types have a limited bandwidth and don't cover this range fully. Sometimes the range of the machine extends beyond the NIR range. For example, some instruments have a second detector that extend the spectral range into the visible domain which is below 700 nm which can come in handy for measuring some quality parameters such as colour.

This of course doesn't mean that all of these instruments have equal performance. There are many other factors involved in performance of an NIR instrument, some of which have nothing to do with the instrument itself! For example, the quality of the NIR calibration model can dramatically influence the performance.

It must be said however that there are times that access to a full scanning range NIR spectrometer can make a significant difference in achieving a better prediction accuracy and precision.

If you are in the process of purchasing a new NIR machine and would like some independent advice, please get in touch with the Aunir team who would be happy to help you.  

 

Image: Some of the main types of NIR instruments in the market and their associated spectral range.

  • DA = Diode array
  • SM = Scanning monochromator
  • FT = Fourier transform
  • MEMS = Micro electro mechanical systems
  • LVF = Linear variable filter