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Why must infrared sample cells have windows that transmit infrared radiation?

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Infrared sample cells must use windows that transmit infrared radiation because many common materials, such as standard window glass, absorb infrared light due to the vibration of their constituent atoms. If the cell windows were made of such materials, they would block the radiation from passing through the sample, making it impossible to perform the analysis.1

To ensure the radiation reaches the sample, these cells must be constructed from specialized optical-grade materials that are transparent to infrared light. Common materials used for these windows include sodium chloride, potassium bromide, and cesium iodide. By using these specific substances, researchers can ensure that the infrared beam effectively interacts with the liquid or gas sample contained within the cell, allowing for accurate spectroscopic measurement.2