A UV spectrophotometer measures the absorbance of ultraviolet and visible light by a sample, providing information about its composition and concentration. The principle relies on the Beer-Lambert Law, which states that the absorbance of a solution is directly proportional to the concentration of the absorbing species and the path length. By measuring the amount of light absorbed at specific wavelengths, the instrument can identify and quantify substances.
Here's a more detailed explanation:
1. Light Source: A UV spectrophotometer uses a light source, typically a tungsten-halogen lamp for the visible region and a deuterium lamp for the ultraviolet region.
2. Monochromator: The light source emits a range of wavelengths. A monochromator, often a grating or prism, is used to isolate a specific wavelength for analysis.
3. Sample Cell: The sample is placed in a cuvette (sample cell) through which the isolated light passes.
4. Detector: The amount of light transmitted through the sample is measured by a detector, which converts the light signal into an electrical signal.
5. Data Processing: The instrument calculates the absorbance (A) or transmittance (T) of the sample based on the ratio of the incident light (I0) to the transmitted light (I). The absorbance is a measure of how much light is absorbed by the sample, and it is directly proportional to the concentration of the absorbing substance according to Beer's Law.
6. Beer-Lambert Law: The relationship between absorbance, concentration, and path length is described by the Beer-Lambert Law: A = ε * b * c, where A is absorbance, ε is the molar absorptivity, b is the path length, and c is the concentration.
In essence: The spectrophotometer shines light of specific wavelengths through a sample and measures how much light is absorbed. This absorption is related to the concentration of the sample and can be used for quantitative analysis.
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