Absorbance

Absorbance 

　　Absorbance measurement is an old technique that is the most widely used spectroscopy for studying liquids and gases, because of its simplicity, nondestructive, accuracy. Absorbance measurement can identify material fingerprint or the concentration of a molecule in solution. Absorbance measurements work equally well for gases and liquids to analyze consumer products as well as industrial application.

　　The most classic introductory chemistry lab experiment of absorbance measurement is a solution in a cuvette, measured in transmission with a dual-beam spectrometer. Modular spectroscopy becomes much more flexible for choosing the wavelength range and resolution needed, moving between sampling optics at quick and easy measurement in the lab or field. Optosky provides a wide range of spectrometers, light sources, and accessories to assist you to create a flexible system to measure solutions and concentrations. The measurement can be performed without altering the sample and can accurately quantify absorbance to no more than 0.001 absorbance units.

　　It's assumed that absorbance measurement is based on scattering is zero, suppose all light not transmitted to the detector is absorbed by the sample, i.e., Transmittance + Absorbance = 1.  It's true for the ideal condition of an infinitely dilute solution of infinitely small particles in a transparent solvent. or it is also true for a wider range of absorbing substances, solvents, and concentrations. Absorbance occurs when the light transmitted encounter the molecule matches frequency vibrations or molecule transitions in energy level. How absorbance is determined by the cross section of the molecule for a particular energy level transition. The chance of absorption depends on both the path length and concentration of the solution, which has been quantified in the Beer’s Law.

What Is Beer-Lambert Law?

       Beer-Lambert Law states that the absorbance of a solution will depend on the concentration of the absorbing molecules and the optical length traveled by light through the solution. At high concentrations, the molecules are closer to each other and begin to interact with each other. This interaction will change several properties of the molecule, and thus will change the attenuation. Beers' Law

　　A=kpc

　　where

　　A is Absorbance

　　K is molar attenuation coefficient

　　b is the optical length traveled by light

　　c is the amount concentration

　　How much light is absorbed can be deducted by light transmitted through the sample. Provided the sample has very low scattering, almost all of the light not absorbed will be transmitted. The transmission will decrease with increasing optical length or concentration.

　　Applications:

　　Environmental: Water quality monitoring, CEMS monitoring

　　Kinetics: concentration changes monitoring during a reaction

　　QA/QC: concentration changes monitoring during manufacturing

　　Chemical reaction monitoring

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