What is a Spectrophotometer?
A Spectrophotometer is a scientific instrument used to measure colour. The intensity of wavelengths is measured and compared with a reference sample. For example, if the colour of a production batch of oil is compared with a known standard colour of oil. The result will be displayed as the degree of absorbance of the difference between them. Wavelength is measured in nanometers (nm).
A spectrophotometer is able to display what chemical substances are present in a sample and exactly how much through calculations of observed wavelengths.
When an object interacts with light, some of the wavelengths of light are absorbed and others are reflected or transmitted (in the case of a coloured but clear liquid). Therefore a red ball absorbs all wavelengths of light except for those in the red part of the spectrum, which it reflects.A blue ball reflects only blue wavelengths. A glass of apple juice transmits green and yellow wavelengths. Fresh snow reflects most of the light that interacts with it and appears white. Black is the absence of reflected light.
There are two main types of spectrophotometers:
Single Beam Spectrophotometers
Measure the light intensity of the beam before and after a sample is inserted. This is optically simpler and more compact.
Double / Dual Beam Spectrophotometers
This compares the light intensity between two light paths, one path containing a reference sample and the other a test sample. These measurements are easier and more stable.
Spectrophotometers can deal with visible light, near-ultraviolet and near-infrared light:
The most common spectrophotometers are used in the UV and visible regions of the colour spectrum. UV-Vis Spectrophotometers measure 200 – 400 nm in the UV range and 400 – 1000 nm in the visible range. Solutions of compounds can be clear but absorb in the UV range.
Inrafared is light with a longer wavelength and lower frequency than visible light. Measurements with infared light are more challenging. It is also used to identify and study chemicals. This is used in quality control, dynamic measurement and forensic analysis.
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