Ultraviolet spectrophotometer is an effective means to study the composition, structure and interaction of substances based on their absorption spectra. The ultraviolet spectrophotometer can arbitrarily choose different wavelengths of light in the ultraviolet visible region. The absorption spectrum of a substance is that the molecules and atoms in the substance absorb the light energy of certain specific wavelengths in the incident light, and the molecular vibrational energy level transition and the electronic energy level transition occur accordingly. Since various substances have their own different molecules, atoms and different molecular space structures, their absorption of light energy will not be the same. Therefore, each substance has its own unique and fixed absorption spectrum curve. The absorbance at certain characteristic wavelengths on the spectrum can be used to determine or determine the content of the substance.
working principle
The absorption spectrum of a substance is essentially that the molecules and atoms in the substance absorb the light energy of certain specific wavelengths in the incident light, and the molecular vibrational energy level transition and the electronic energy level transition occur accordingly. Because various substances have their own different molecules, atoms and different molecular spatial structures, their absorption of light energy will not be the same. Therefore, each substance has its own unique and fixed absorption spectrum curve, and the content of the substance can be judged or determined according to the absorbance at certain characteristic wavelengths on the absorption spectrum, which is the basis of qualitative and quantitative analysis of spectrophotometry . Spectrophotometric analysis is an effective means to study the composition, structure and interaction of substances based on their absorption spectra.
And because many substances have characteristic absorption peaks in the ultraviolet-visible region, ultraviolet spectrophotometry can be used to determine these substances (quantitative analysis and qualitative analysis). Ultraviolet spectrophotometry is based on Lambert-Beer law.
Lambert-Beer's law (Lambert-Beer) is the basic law of light absorption, commonly known as the law of light absorption, and is the basis and basis for quantitative analysis of spectrophotometry. When the wavelength of the incident light is constant, the absorbance A of the solution is a function of the concentration C of the light-absorbing substance and the thickness l (absorption optical path) of the absorption medium.
Spectrophotometry
First determine the experimental conditions, and measure the absorption peak of the standard substance and its corresponding wavelength value under this condition; and then within the selected wavelength range (, respectively, the absorbance and solution concentration of the (different concentration) standard solution are horizontal and vertical Coordinate draw the standard curve of the compound solution to obtain the corresponding mathematical equation; then prepare the solution to be tested under the same experimental conditions, measure the absorbance of the solution to be measured, and use the obtained standard curve equation to find the required solution Determination of the content of compounds
Range of use
Any organic compound with an aromatic ring or conjugated double bond structure can be used for drug identification, purity inspection, and content determination based on the absorbance measured at a specific absorption wavelength.
Wavelength range
Visible-ultraviolet spectrophotometer. Its application wavelength range is 200-400nm ultraviolet region, 400-850nm visible region. It is mainly composed of radiation source (light source), dispersion system, detection system, absorption cell, data processor, automatic recorder and display.
application
1 Test substances
According to some characteristic absorption on the absorption spectrum, especially the maximum absorption wavelength, although ax and molar absorption coefficient are commonly used physical parameters of the test substance. This has a wide range of applications in drug analysis. In the pharmacopoeia at home and abroad, the maximum absorption wavelength and absorption coefficient of the ultraviolet absorption spectrum of many drugs have been loaded into it, which provides a good means for drug analysis.
2 Comparison with standards and standard spectra
The analytical sample and the standard sample were prepared in the same solvent at the same concentration, and the ultraviolet-visible absorption spectra were measured under the same conditions. If the two are the same substance, the spectra of the two should be exactly the same. If there is no standard sample, it can also be compared with the existing standard spectrum. This method requires accurate instruments, high precision, and the same measurement conditions.
3 Compare the consistency of the absorption coefficient of the maximum absorption wavelength
4 Purity inspection
5 Infer the molecular structure of the compound
6 Determination of hydrogen bond strength
Experiments show that different polar solvents have different hydrogen bond strengths, which can be used to determine the hydrogen bond strength of compounds in different solvents using ultraviolet spectroscopy to determine which solvent to choose.
7 Determination of complex composition and stability constant
8 Reaction kinetics research
9 Application in organic analysis
Organic analysis is a science that studies the separation, identification and composition of organic compounds. It is a comprehensive discipline developed on the basis of organic chemistry and analytical chemistry.
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