Wavelength Absorbance Graph
私. 導入
The wavelength absorbance graph is a graphical representation of the relationship between the wavelength of light and the amount of light absorbed by a substance. It is an essential tool in spectroscopy and is commonly used to identify and analyze substances based on their absorption properties.
Ⅱ. Principles of Absorbance
A. Absorption of Light
When light passes through a substance, it can be absorbed, transmitted, or reflected. Absorption occurs when the energy of the light matches the energy required to excite the electrons in the substance. This absorption leads to a decrease in the intensity of the transmitted light.
B. Beer-Lambert Law
The relationship between the absorbance of a substance and its concentration can be described by the Beer-Lambert law: A = εlc, where A is the absorbance, ε is the molar absorptivity, l is the path length of the sample, and c is the concentration of the substance. This law forms the basis for quantitative analysis using absorbance measurements.
Ⅲ. Experimental Setup
A. Spectrophotometer
The wavelength absorbance graph is typically obtained using a spectrophotometer. This device measures the intensity of light before and after passing through a sample. It utilizes a monochromator to select a specific wavelength of light and a photodetector to quantify the intensity.
B. Sample Preparation
To obtain a wavelength absorbance graph, a series of samples with known concentrations of the substance of interest are prepared. The samples should cover a range of concentrations to establish a linear relationship between absorbance and concentration.
Ⅳ. Procedure
A. Wavelength Scan
The spectrophotometer is set to scan a range of wavelengths, typically from ultraviolet (UV) to visible or near-infrared (NIR) regions. The intensity of the transmitted light is recorded at each wavelength.
B. Data Analysis
The recorded data is plotted on a graph with wavelength on the x-axis and absorbance on the y-axis. A curve or peak in the graph represents the wavelength(s) at which the substance absorbs the most light. This information can be used for substance identification and characterization.
V. アプリケーション
A. Qualitative Analysis
The wavelength absorbance graph can be used to identify unknown substances based on their absorption patterns. Each substance has a unique wavelength at which it absorbs light, allowing for the identification of compounds in mixtures or solutions.
B. Quantitative Analysis
By measuring the absorbance of a series of samples with known concentrations, a calibration curve can be established. This curve can then be used to determine the concentration of an unknown sample by measuring its absorbance and using the equation derived from the Beer-Lambert law.
VI. 結論
The wavelength absorbance graph is a valuable tool in spectroscopy, enabling both qualitative and quantitative analysis of substances. Its ability to identify compounds based on their absorption patterns and quantify their concentrations makes it an essential technique in various fields such as chemistry, biology, and environmental science.
