Absorbance: refers to the logarithm to the base 10 of the ratio of the incident light intensity before the light passes through the solution or a substance to the transmitted light intensity after the light passes through the solution or substance (ie lg(I0/I1)), Among them, I0 is the incident light intensity, and I1 is the transmitted light intensity. The factors affecting it are solvent, concentration, temperature and so on.
The absorption coefficient is related to the wavelength of the incident light and the substance through which the light passes. As long as the wavelength of the light is fixed, the absorption coefficient of the same substance will not change.
When a beam of light passes through a light-absorbing substance (usually a solution), the solute absorbs the light energy and the intensity of the light decreases. Absorbance is a physical quantity used to measure the degree to which light is absorbed.
The absorbance is represented by A.
A=abc, where a absorbs the coefficient, the unit is L/(g cm), b is the distance that the light passes in the sample (usually the thickness of the cuvette), the unit is cm, and c is the solution concentration, the unit is g/L
A=Ecl
Factors affecting absorbance are b and c. a is a constant related to the solute. Furthermore, temperature affects A by affecting c.
The symbol A represents the degree of absorption of light by the substance. lg(I0/I1) In the formula, I0 is the intensity of incident light of a beam of parallel light passing through a uniform liquid medium; It is the intensity of transmitted light; T is the transmittance. The larger the value of A, the greater the absorption of light by the substance. According to Beer's law, the absorbance is proportional to the concentration c of the light-absorbing substance, and the calibration curve of photometric analysis can be obtained by plotting A against c. In a multi-component system, if the light-absorbing particles of each component do not interact with each other, then the absorbance is equal to the sum of the absorbance of each component. This rule is called the additivity of absorbance. Based on this, simultaneous determination of multiple components and determination of equilibrium constants of certain chemical reactions can be carried out. In the absorbance measurement, in order to offset the absorption and reflection of the incident light by the absorption cell and the absorption and scattering of the incident light by solvents and reagents, a double-beam Spectrophotometer can be used, and an absorption cell with the same optical properties and equal thickness can be selected. Hold the solution to be tested and the reference solution separately.
