NIR spectra are notoriously difficult to interpret mainly due to broad, overlapping and non-specific nature of their absorption bands. Nevertheless there is a wealth of information hidden in the peaks and troughs of these seemingly featureless entities to the extent that they are called finger prints. A great deal can be learned from some basic understanding of NIR spectral features. This skill can come in handy in many situations ranging from trouble shooting through to classification and outlier detection.
In this new column we will try to share some Light Bite lessons on interpretation of NIR spectra of food and feed samples without trying to get too involved with the technical complexities of this subject matter. Here goes...
Illuminating Spectra - Part 1: Can you spot the oil?!
Oil (or fat) has very characteristic absorption bands that can’t be easily missed in NIR spectra, especially when oil concentration is high in a sample. Oil bands appear as distinct duplets at two regions in the NIR range: the region around 1700 nm and the region around 2300 nm.
The left branch of the duplet is normally more prominent. At lower concentration of oil the duplet at 1700 nm tends to get smoothed out turning into a little lump.
An example below shows spectra form two agricultural samples one with high oil content (blue line) and the other one with very little oil (green line).