UV visible spectrophotometerIt is a widely used analytical instrument, applied in various fields such as pharmaceuticals, medical and health care, chemical engineering, metrology science, agriculture, forestry, fisheries, etc. It is used for qualitative analysis, purity inspection, structural analysis, determination of complex composition and stability constants, reaction kinetics research, etc.

UV visible spectrophotometerPrinciple Introduction:

The quantitative analysis basis of UV visible spectrophotometry is Lambert Beer's law. The absorbance of a substance at a certain concentration is directly proportional to the thickness of its absorbing medium.
The color of a substance is closely related to its electronic structure. When radiation (photons) causes electronic transitions, causing (or ions) to rise from the ground state to the excited state, (or ions) will exhibit absorption in the visible or ultraviolet region. The occurrence or change of color is related to the deformation of the normal electronic structure of the molecule. It contains one or more chromogenic genes (i.e. atomic groups with unsaturated bonds), and radiation can cause a change in the energy of electrons.
If two chromophores are separated by a carbon atom, a conjugated group is formed, which will shift the absorption band towards longer wavelengths (i.e. red shift) and significantly increase the intensity of the absorption band. When it contains chromophore groups (groups with unshared electron pairs), a red shift effect will also occur. Common chromophore groups include: - OH-NH2, - SH, - Cl, - Br, - I

UV visible spectrophotometerApplication Introduction:

(1) Quantitative analysis
According to the Lambert Beer law, the concentration of a sample is directly proportional to its absorbance. The higher the concentration, the higher the absorbance value. Therefore, quantitative analysis is more commonly used in spectrophotometers, and there are many types of quantitative analysis. Here are several commonly used quantitative analysis methods:
A、 Method: Method is one of the most commonly used analytical methods in UV visible spectrophotometry. This is an analytical method based on the Lambert Beer law A=ε bC. The ε value of a substance at a certain wavelength is a constant, and the optical path length of a quartz cuvette is known and also a constant. Therefore, a UV visible spectrophotometer can be used to measure the absorbance value A of the sample solution at the λ max wavelength. Then, according to Lambert Beer's law, C=A/ε b can be calculated to determine the content or concentration of the sample solution.
B、 Standard method: At the selected wavelength, under the same testing conditions, test the absorbance A of the standard sample solution C and the absorbance A of the tested sample solution C. Then, calculate the concentration or content of the sample solution according to the following formula.
C sample=A sample/A standard × C standard
C、 Standard curve method
The commonly used quantitative analysis method for UV visible spectrophotometers is the standard curve method. First, prepare a solution of a certain concentration using standard substances, and then prepare the solution into a series of standard solutions. At a certain wavelength, test the absorbance of each standard solution, with the absorbance value as the vertical axis and the corresponding concentration of the standard solution as the horizontal axis, and draw a standard curve. Afterwards, measure the absorbance value of the sample solution according to the standard curve drawing program, and find the corresponding concentration or content of the sample solution on the standard curve.
A、 Other analytical methods
In addition to the above-mentioned analysis methods, there are also commonly used analysis methods such as specific absorption coefficient method, small two multiplication, solution cubic range method, and differential spectrophotometry.
(2) Qualitative analysis
If the large absorption peak wavelength λ max, small absorption peak wavelength λ min, large molar absorption coefficient ε max, as well as the number, position, and inflection point of the absorption peaks in the UV absorption spectrum of an unknown substance are consistent with the standard spectral data, it can be considered as the same compound. The main purpose of qualitative analysis is to know what substances are present in the analyzed sample.
Quantitative analysis and qualitative analysis are the two main functions of a spectrophotometer, especially quantitative analysis. Other analyses should have developed from these two major functions.