Ultraviolet and visible Spectroscopy(UV-vis)
Introduction:
UV-Vis spectroscopy, also known as UV-Visible analysis, is a widely used technique in chemistry, biosciences, engineering, and environmental sciences. This method is based on measuring the amount of light absorbed by a sample in the ultraviolet and visible wavelength ranges. Its applications are highly diverse, with the primary use being the determination of the concentration of chemical compounds, ions, and molecules.
Additionally, UV-Vis analysis is used for measuring energy band gaps in semiconductors, studying reaction progress, monitoring chemical reactions, and determining nanoparticle size. Electromagnetic waves in the visible and ultraviolet light spectrum are directed at the sample, where phenomena such as absorption, reflection, and refraction occur. Measuring nanoparticle size is among its other applications.
Test Principle:
When an electromagnetic beam interacts with a sample, certain frequencies are absorbed, weakening the beam. Every material has unique absorption mechanisms, and when the outgoing beam is analyzed using a prism, the intensity of each wavelength is measured by a detector. The results are displayed as a graph, which helps identify the compounds present in the sample.
The absorption intensity depends on the concentration of the substance, allowing UV-Vis spectroscopy to be used for comparing different quantities or measuring concentrations. The relationship between absorption and concentration follows the Beer-Lambert law, which states that absorption is proportional to the path length and concentration of the substance.
This law also applies to multi-component solutions, provided that there are no interactions between different species. At high concentrations, particle interactions may affect absorption capacity, requiring these factors to be considered.
Measurement Benefits:
1. Measuring light absorption
2. Determining solution concentration
3. Studying drug release
4. Analyzing the absorption and transmission properties of a material within a specific wavelength range
5. Observing changes in absorption and transmission at a specific wavelength over time
6. Measuring absorption at multiple specific wavelengths
7. Determining the energy band gap (using the DRS technique)
8. Qualitative and quantitative identification of one or more specific species in a mixture
Test Conditions:
Samples can be in the form of a solution, emulsion, or powder.
Powdered samples must be dispersed in a suitable medium (usually water or alcohol) to form an emulsion.
For emulsified samples, it is recommended to use an ultrasonic bath before testing to achieve better results.
Results Interpretation:
Interpreting UV-Vis analysis results involves several key steps:
1. Spectrum Plotting:
After the analysis, a spectrum is plotted, showing absorption intensity (A) on the vertical axis and wavelength (λ) on the horizontal axis. Peaks in the spectrum indicate specific absorption regions.
2. Peak Identification:
The spectrum peaks correspond to absorbed wavelengths. This information can be used to identify chemical substances in the sample based on a known database.
3. Measuring Absorption Intensity:
The absorption intensity at each wavelength provides information about the concentration of the substance, following the Beer-Lambert law.
4. Results Analysis:
High absorption: Usually indicates a high concentration of the absorbing substance.
Low absorption: May indicate a low concentration or the absence of the substance.
Time-based absorption measurements: Can reveal how absorption changes over time, providing insights into reaction dynamics or sample stability.