Spectrophotometry is one of the most commonly used and effective tools for analysts.Almost every analytical laboratory is dependent on uV-vis spectrophotometers.UV spectrophotometer has the following main characteristics.
1. High sensitivity
Due to the large amount of synthesis of new chromogenic agents and the encouraging progress in the application research, the sensitivity of element determination has been promoted, especially the application research of multi-complex and various surfactants, the molar absorbance coefficient of many elements has been increased from tens of thousands to hundreds of thousands.
2. Be selective
At present, some elements can be determined directly by photometric method as long as appropriate color developing conditions are controlled, such as the determination of cobalt, uranium, nickel, copper, silver, iron and other elements, and there are satisfactory methods.
3. High accuracy
For general spectrophotometry, the relative error of concentration measurement is within the range of 1 ~ 3%. If differential photometry is used for measurement, the error can be reduced to 0.x %.
4. Wide range of applicable concentrations
It can range from constant (1% ~ 50%)(especially using differential method) to trace (10-8 ~ 10-6%)(after preenrichment).
5. Analysis cost is low, easy to operate, fast and widely used
Because all kinds of inorganic substances and organics are absorbed in the uV-visible region, they can be measured by this method.So far, this has been done for almost all elements on the periodic table, with the exception of a few radioactive and inert elements.Photometry accounts for 28% of the papers published internationally, and 33% of the papers published in China.
1. Substance verification
Absorption, especially the maximum absorption wavelength Max and molar absorption coefficient, is a common physical parameter for the determination of a substance according to some characteristics of the absorption spectrum.
2. Compare with standard materials and standard diagrams
The analysis sample and the standard sample were prepared in the same solvent at the same concentration and the uV-VIS spectra were determined under the same conditions.If they are the same substance, the spectra of the two should be identical.If a standard sample is not available, comparisons can also be made against an existing standard spectrogram.This method requires the instrument to be accurate, precise and the measuring conditions to be the same.
3. Compare the consistency of the absorption coefficients of the maximum absorption wavelength
Because the ULTRAVIOLET absorption spectrum contains only 2 ~ 3 wide absorption bands, and the ultraviolet absorption spectrum is mainly produced by the chromophore within the molecule in the ultraviolet region, and has little relationship with the molecule and other parts.Different molecular structures with the same chromophore do not affect the uv absorption spectrum of chromophore in larger molecules. Different molecular structures may have the same UV absorption spectrum, but their absorption coefficients are different.If the absorption wavelength and absorption coefficient of the analysis sample and the standard sample are the same, the analysis sample and the standard sample can be considered to be the same substance.
4. Study on reaction kinetics
Some chemical reaction rate constants can be obtained by means of spectrophotometry, and reaction activation energies can be obtained from velocity data obtained at two or more temperatures.
5. Purity test
Ultraviolet absorption spectrum can determine the compounds contain trace amounts of impurities with ultraviolet absorption.Impurities in the compound can be detected if there is no obvious absorption peak in the ultraviolet visible region of the compound, but its impurities have a strong absorption peak in the ultraviolet region.
6. Determination of hydrogen bond strength
The hydrogen bond strength of different polar solvents is also different. Ultraviolet spectrum can be used to determine the hydrogen bond strength of compounds in different solvents to determine which solvent to choose.
7. Determination of complex composition and stability constant
Metal ions often form complexes with organic compounds, most of which are absorbable in the uV-visible region, and their composition can be studied by spectrophotometry.
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