Identifying Organic Contaminants in Sub Tier Castings Using FTIR Fingerprinting
Attenuated total reflectance FTIR identifies organic parting agents on raw castings before expensive coating processes fail on customer lines.
Infrared Absorption Bands
Meaning
Spectral signatures resulting from the absorption of electromagnetic radiation by molecular vibrations allow for the identification of chemical functional groups in a substance. Each set of infrared absorption bands corresponds to specific stretching or bending motions within the molecules of the sample. Scientists use these patterns as a fingerprint to verify the identity of raw materials and finished products.
Frequency Identification
Absorption occurs at precise wavelengths that match the natural resonant frequencies of the chemical bonds. The position of infrared absorption bands is typically measured in wavenumbers, ranging from 4000 to 400 inverse centimeters. High-frequency regions often indicate the presence of hydrogen-bonded groups like hydroxyl or amine functions.
Lower frequencies are associated with heavier atoms or complex skeletal vibrations of the entire molecule.
Structural Correlation
Relationship between the intensity of a peak and the concentration of the corresponding chemical group follows the Beer-Lambert law. When infrared absorption bands are analyzed, the shape and width of the peak provide information about the molecular environment and inter-molecular forces. A sharp peak suggests a well-defined crystalline structure, while broad bands indicate an amorphous or hydrogen-bonded system.
This data is used to differentiate between different grades of polyethylene or to detect the presence of additives.
Measurement Reliability
Accuracy of the spectral data depends on the resolution of the spectrometer and the quality of the sample preparation. Variations in infrared absorption bands can occur due to changes in the physical state of the material or the presence of moisture. In the context of Chinese import inspections, the consistency of these bands against a known reference standard is used to identify counterfeit or mislabeled chemicals.
Laboratorians must account for instrument noise and atmospheric CO2 when interpreting the results.