What is penetration depth of ATR FTIR?
ATR-FTIR spectroscopy is a powerful analytical tool that provides detailed information about the surface chemical composition and structure of materials. It utilizes the principle of total internal reflection (TIR), where infrared light undergoes multiple reflections between a high-refractive-index crystal (e.g., diamond, germanium) and the sample, generating an evanescent wave that penetrates the sample surface.
Due to the shallow penetration depth of the evanescent wave, typically only a few micrometers, ATR-FTIR spectroscopy is particularly well-suited for analyzing thin films, coatings, and surface layers of materials.
Advantages of ATR-FTIR Spectroscopy
• Minimal Sample Preparation: Since ATR only probes the shallow region of the sample, it eliminates the need for extensive sample preparation steps, such as slicing, grinding, or dissolving, which is particularly beneficial for analyzing difficult-to-prepare or destructive samples.
• Analyzing Heterogeneous Samples: ATR can provide localized information about different regions or layers, making it ideal for analyzing heterogeneous samples with varying compositions or structures.
• High Sensitivity: Due to the intimate interaction between the evanescent wave and the sample surface, ATR-FTIR spectroscopy can achieve high-sensitivity signals, enabling the detection of even trace amounts of surface components.
Limitations of ATR-FTIR Spectroscopy
• Limited Penetration Depth: ATR's shallow penetration depth may not provide accurate information for components located deeper within the sample's bulk.
• Signal Intensity Affected by Penetration Depth: As the penetration depth increases, the infrared signal weakens due to absorption and scattering processes within the sample, potentially affecting spectral comparison or quantitative analysis.
Conclusion
ATR-FTIR spectroscopy offers a robust analytical technique for gleaning valuable insights into the surface chemistry and structure of materials. Its shallow sampling depth and high sensitivity make it an excellent choice for analyzing thin films, coatings, and heterogeneous samples. However, when employing ATR-FTIR spectroscopy, one should also consider the potential impact of its limited penetration depth.