Construction of a calibration model stable to structural

changes in a grain analyzer

P.A. Luzanov, K.A.Zharinov , V.A.Zubkov

LUMEX Ltd., St. Petersburg, Russia

The InfraLUM FT-10 analyzer optical diagram

 1. Radiation source unit 5. Sampler 2. Interferometer 6. Cell with a sample 3. Optical unit 7. Photodetector 4. Cell compartment

Calibration equation

y=XT *p+e

y is the vector of the reference values of dimension n, n is the number of spectra included in the calibration;

XT is the transpose of the matrix of the spectral data of dimension f by n, f being the number of the discrete wavenumbers at which the spectra were measured;

p is the calibration factors vector of dimension f; ande is the error vector of dimension n.

Calibration of the instrument

- protein

wheat properties the ranges of reference

values 10.5-15.7%

15.1-26.2%- gluten

Calibration of the instrument

Results of verification of the initial calibrations on the

instrument with different beamsplitters by validation using

additional set of samples

Algorithm of calibration model correction, step 1

Selection a calibration set of samples

Registration their spectra on an instrument

Construction a PLS calibration model allowing for the current condition of the analyzer

Algorithm of calibration model correction, step 2

Selection a set of representative samples

from the calibration set of samples with the maximum and minimum values of the score parameter for each of the analyzed properties

Algorithm of calibration model correction, step 3

Changes are artificially introduced in the design features of the instrument, which lead to the largest deviation of the analysis results from the initial calibration model

Algorithm of calibration model correction, step 4

Registration the transmittance spectra of the selected samples on the instrument with the changes introduced in its design features

Algorithm of calibration model correction, step 5

Construction a PLS calibration model using the spectra of the calibration samples recorded on the original instrument and the spectra of the samples from the selected set recorded on the instrument with changes introduced in its design features

Comparison of calibrations

Initial calibrations 

Calibrations corrected allowing for the replacement of the beamsplitter

Verification of calibrations on the instrument with different beamsplitters

Initial calibrations 

Calibrations corrected allowing for the replacement of the beamsplitter

Conclusions

The study of various structural components of the instrument under investigation and the extent of their influence on variation in calibration and, accordingly, on the quality of the analysis, has demonstrated that one of the main affecting factors is the beamsplitter;

The obtained experimental data have confirmed the operability of the algorithm used for constructing a calibration model that is stable to a change in the performance characteristics of the instrument due to its ageing, repair, replacement, or readjustment of any of its units.