Definition
An infrared spectrometer is an instrument that analyzes the absorption characteristics of infrared radiation based on substances. It is used for qualitative and quantitative analysis of substances by measuring the absorption spectrum of the sample in the infrared light region to obtain information on molecular vibration and rotational energy level transitions. This technology is widely used in chemical, materials, pharmaceutical, food and environmental monitoring fields.
Principle
The core principle of infrared spectroscopy analysis is molecular vibration and rotational energy level transition. When infrared light irradiates a sample, a specific wavelength of infrared light is absorbed if the photon energy matches the vibration or rotational energy level difference of the chemical bonds in the molecule. The absorption intensity is related to the concentration and molecular structure of the substance, according to the Lambert-Beale law:
A = εbc
Where A is absorbance, ε is the molar absorbance coefficient, b is the path length, and c is the sample concentration. By recording absorption at different wavelengths, infrared spectra reflecting molecular characteristics can be obtained.
Measurement method
Common measurement methods include transmission, attenuated total reflectance, and diffuse reflectance. Transmission methods are suitable for transparent or translucent samples, where the sample is placed in the optical path and the transmitted light intensity is measured directly. Attenuated total reflectance is commonly used for liquid, colloidal or surface analysis to obtain information on the surface of a sample using total reflection. The diffuse reflection method is mostly used for powder or opaque solid samples to obtain spectral data by detecting scattered light. Depending on the sample state and analytical needs, the corresponding method can be selected with appropriate sample preparation techniques, such as tablet pressing or liquid film method.
Influencing factors
Infrared spectroscopy measurements are influenced by a variety of factors. Sample preparation methods, such as thickness, uniformity, and particle size, can alter spectral characteristics. Water vapor and carbon dioxide in the environment can interfere with specific wave bands. Instrument parameter settings, including resolution, number of scans, and signal-to-noise ratio, can also affect data quality. In addition, changes in sample temperature can cause peak shifts or shape changes. These variables need to be controlled during the analysis to ensure the reliability of the results.
Application
Infrared spectrometers have practical value in many fields. In chemical research, it is used to identify functional groups and molecular structures. The pharmaceutical industry uses it for raw material identification and quality control. It can be used in food testing for ingredient analysis and adulteration identification. Environmental monitoring can detect pollutants such as organic volatiles. In materials science, it is used for polymer characterization and surface analysis. These applications are based on the high specificity of infrared spectroscopy for the recognition of molecular fingerprint regions.
Selection
When choosing an infrared spectrometer, it is necessary to comprehensively consider the technical parameters and application requirements. The spectral range should cover the mid-infrared region, and some applications need to be extended to the near-infrared or far-infrared. Resolution affects peak separation ability, and medium resolution is available for general analysis. Detector type such as DTGS or MCT is selected according to sensitivity requirements. The functionality and data processing capabilities of the operating software are also worth paying attention to. In addition, instrument stability, maintenance costs, and subsequent technical support are factors that need to be evaluated in actual work. Comprehensive judgment based on specific sample types and analysis goals can help to select suitable instruments.