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How to use Shimadzu infrared spectrometer for quantitative analysis?
Date: 2025-12-07Read: 0
Shimadzu Infrared SpectrometerQuantitative analysis is based on the corresponding relationship between spectral absorbance and component concentration at specific wavenumbers. By measuring and calculating this relationship, the content of the target component in the mixture can be determined. The usage process requires sequential completion of sample preparation, spectral acquisition, feature selection, calibration establishment, and result calculation, while maintaining consistency in each step to reduce errors.
Sample preparation requires ensuring reproducible optical contact and effective signal strength. Solid samples are commonly compressed or attenuated total reflection methods. During compression, pressure and uniformity should be controlled to ensure consistent particle distribution; The attenuated total reflection method requires selecting a crystal that matches the refractive index of the sample and ensuring a smooth contact surface. Liquid samples can be obtained using liquid film method or liquid pool method, with stable liquid film thickness and clean and scratch free pool windows. The gas sample should be filled into a dedicated gas chamber to ensure that the pressure is consistent with the path length. Different forms of samples should avoid mixing impurities or bubbles during sample preparation to prevent additional absorption interference with quantitative peaks.
Spectral collection should be carried out under uniform conditions. Choose an appropriate scanning range and resolution to ensure that the target absorption peak is clear and does not overlap too much with adjacent peaks. Background collection should be completed under the same optical path conditions, and the background material should be consistent or known with the sample matrix in order to effectively deduct environmental and container absorption. To reduce the influence of random noise, multiple scans and accumulations can be performed to make the spectrum smooth and the features stable. During the collection process, the instrument status should be kept unchanged, including light source intensity, detector gain, and environmental temperature and humidity, to prevent signal drift.
The selection of characteristic wavenumbers is a key step in quantitative analysis. An absorption peak that is only related to the target component should be found in the sample spectrum, and this peak should exhibit a linear response within the concentration range to be measured. Avoid using areas that overlap with other components or are significantly disturbed by moisture, carbon dioxide, etc. If necessary, highlight the target peak through differential spectrum or derivative processing, but verify that the relationship between peak area or peak height and concentration remains stable after processing. After selecting the wavenumber, record the response values of the position in the spectra of different concentration standards to form a calibration data set.
The calibration process requires the use of standard samples with known concentrations to establish corresponding relationships. The composition and physical form of the standard sample should be consistent with the sample to be tested, covering the expected concentration range, and measured at at least five different concentration points to verify the linearity and range applicability of the response. Perform linear regression with concentration as the independent variable and peak area or peak height as the dependent variable to obtain the calibration equation and correlation coefficient. If the correlation coefficient is low, the repeatability of sample preparation, selection of characteristic wavenumbers, or instrument status should be checked, and outliers should be removed and re fitted. Polynomial or segmented calibration can be considered for nonlinear intervals, but the applicable scope must be limited.
When quantitatively calculating, the characteristic response values of the test sample measured under the same conditions are substituted into the calibration equation to obtain the concentration value. The sources of uncertainty in the results need to be evaluated, including sample reproducibility, spectral noise, calibration residuals, and environmental fluctuations. If necessary, conduct parallel measurements, calculate the mean and dispersion, and determine whether the analysis requirements are met. If there are differences between the matrix of the test sample and the standard sample, the influence of matrix effects should be investigated, which can be corrected by adding internal standards or using the standard addition method.
useShimadzu Infrared SpectrometerThe core of quantitative analysis lies in the consistency between sample preparation and collection, the specificity of characteristic wavenumbers, and the reliability of calibration models.