FTIR (Fourier-transform infrared) spectroscopy is used to measure the molecular structure of a sample. This technique involves the analysis of how infrared light interacts with the chemical bonds in a sample, providing insights into the types of bonds and functional groups present.
Detailed Explanation:
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Principle of FTIR Spectroscopy: FTIR spectroscopy works by exposing a sample to infrared light, which is absorbed by the sample at specific frequencies corresponding to the vibrational modes of its constituent molecules. Each type of bond (e.g., C-H, N-H, O-H) absorbs light at specific wavelengths, creating a unique pattern of absorption peaks in the spectrum. This pattern serves as a molecular "fingerprint" that can be used to identify the components of the sample.
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Sample Preparation and Measurement Methods: The method of measurement in FTIR depends on the form of the sample. For powder samples, common methods include the KBr pellet method, the Nujol method, and the diffuse reflection method. The KBr pellet method involves diluting the sample in potassium bromide and pressing it into a solid pellet using a hydraulic press. The Nujol method uses a mineral oil mull to prepare the sample. The diffuse reflection method, increasingly popular with the advent of FTIR, allows for the direct measurement of powder samples without the need for extensive sample preparation. Attenuated total reflection (ATR) is another technique that enables direct measurement of samples, including powders, by placing the sample in contact with a crystal that reflects the infrared light through the sample.
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Applications and Advantages: FTIR is widely used in various fields, including chemistry, material science, and pharmaceuticals, for qualitative and quantitative analysis. It is particularly useful for identifying unknown substances, monitoring the progress of chemical reactions, and determining the purity of compounds. The use of in situ FTIR reaction monitoring, for example, can reduce the number of experiments needed, speed up the process of scaling up a reaction, and improve safety and yield by providing real-time analysis of the reaction mixture.
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Comparison with Other Techniques: While XRF (X-ray fluorescence) spectroscopy uses X-rays to analyze samples, FTIR uses infrared light. This fundamental difference in the type of radiation used leads to different types of information being gathered. XRF is primarily used for elemental analysis, whereas FTIR focuses on molecular structure and functional groups.
In summary, FTIR spectroscopy is a powerful analytical tool used to measure the molecular structure of samples by analyzing the absorption of infrared light by the chemical bonds in the sample. The choice of measurement method depends on the sample's form, with various techniques available to accommodate different sample types.
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