The spectrophotometer uses a light source that can generate multiple wavelengths and passes through a series of spectrometers to generate a light source with a specific wavelength. After the light passes through the test sample, part of the light is absorbed, the absorbance of the sample is calculated, and the concentration of the sample is converted. . The absorbance of the sample is proportional to the sample concentration.
When the monochromatic radiation passes through the solution of the measured substance, the amount absorbed by the substance is proportional to the concentration of the substance and the thickness of the liquid layer (length of the optical path). The relationship is as follows:
A=-lg(I/I0)=-lgT=kLc
Where: A is the absorbance;
I0 is the incident monochromatic light intensity;
I is the transmitted monochromatic light intensity;
T is the material transmittance;
k is the molar absorption coefficient;
L is the path length of the material being analyzed, ie the side length of the cuvette;
c is the concentration of the substance;
The selective absorption wavelength of light by a substance and the corresponding absorption coefficient are the physical constants of the substance. When the absorption coefficient of a pure substance under certain conditions is known, the test sample can be formulated into a solution under the same conditions, and the absorbance can be determined. The content of the substance in the test sample can be calculated from the above formula. In the visible light region, except for the absorption of light by certain substances, many substances are not absorbed by themselves but can be added under a certain condition or processed to make them colorable. It is also called colorimetric analysis. Due to the fact that there are many factors that affect the color depth during coloration, and instruments with poor purity of monochromatic light are often used, standard products or reference materials are used for simultaneous measurement.
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