If chemical bonds behaved exactly like weak springs then quantum mechanics would restrict their vibration to just two states and there would be very few absorptions in the NIR region. Absorptions in the NIR region (780 – 2500 nm) are generated from fundamental vibrations by two processes; overtones and combinations. Overtones can be thought of as harmonics. So every fundamental will produce a series of absorptions at approximate integers. Combinations are rather more complex. NIR absorptions are at a higher state of excitement so they require more energy than a fundamental absorption. Combinations arise from the sharing of NIR energy between two or more fundamental absorptions. While the number of possible overtones from a group of fundamental absorptions in a molecule are limited to a few, a very large number of combinations will be observed. The effect of all these absorptions combine to make many NIR spectra to look rather uninteresting and to consist of only a few rather broad peaks. Figure 2 is an NIR spectrum of chloroform, CHCl3, the molecule contains only one hydrogen atom but all the absorption in its spectrum are caused by this single atom.
Spectrolab offer a wide range of NIR spectrometers with many options for wavelength range and sensitivity
The hardware consists of a solid state miniature spectrometer and an InGas
detector coupled to a fibre optic probe. A light source is also available along
with appropriate applications software. The instrument is simple, inexpensive
and highly reliable.
There are many applications for this powerful spectroscopic technique and
include
Food analysis Particle blending Pharmacy
Agriculture Grain Moisture
Milk Fats And oil QC
Gas analysis Physical Sciences Semiconductor
Radiometry Plastics sorting Soil analysis
Plant and leaf dynamics Environment Clinical
Near-infrared spectroscopy is widely applied in agriculture for determining the
quality of grains and grain products, oilseeds, coffee, tea, spices, fruit,
vegetables, sugarcane, beverages, fats, and oils, dairy products, eggs, meat and
other products. It is widely used to quantify the composition of agricultural
products because it meets the criteria of being accurate, reliable, rapid, nondestructive and inexpensive.
