Infrared Composition Analyzers: Principle and Operation

Infrared (IR) composition analyzers are widely used in food, pharmaceutical, chemical, and agricultural industries to identify and quantify components in a sample. They are fast, non-destructive, and suitable for both laboratory and online analysis.

Working Principle

IR analyzers are based on the interaction between infrared radiation and molecules. When IR light passes through a sample, certain chemical bonds absorb energy at specific wavelengths. These absorptions correspond to molecular vibrations, such as stretching and bending of O–H, C–H, N–H, C=O, and other functional groups. Because different substances have different molecular structures, their IR spectra produce unique absorption patterns, often called “fingerprints.”

In quantitative analysis, the amount of absorbed light is related to the concentration of the target component. By building calibration models with known samples, the analyzer can convert spectral data into concentration values. Many modern instruments use Fourier transform infrared (FTIR) technology, which collects an interferogram and converts it into a spectrum. Near-infrared (NIR) analyzers are also common for rapid composition analysis, especially in production environments.

Operation Steps

First, prepare the instrument. Check the power supply, purge gas, and environmental conditions. Turn on the analyzer and allow it to warm up and stabilize. If required, run a self-test or diagnostic check.

Second, collect a background or reference spectrum. This step corrects for the instrument’s own response, air components such as water vapor and carbon dioxide, and the optical path. Always collect a fresh background when conditions change.

Third, prepare the sample. The sample must be representative and free from contamination. Liquids may be placed in a suitable cell, solids may be powdered or pressed into a pellet, and powders may be measured by diffuse reflectance. For online analysis, ensure the sampling interface is clean and the material flow is stable.

Fourth, perform the measurement. Place the sample in the sampling accessory, select the appropriate method, and start the scan. The instrument records the spectrum and processes it automatically.

Fifth, analyze the results. Compare the spectrum with reference libraries for identification, or apply a calibration model for quantitative results. Check peak positions, peak heights, and baseline quality. If the result is abnormal, repeat the measurement and verify sample preparation.