BUCHI NIRCal - Manual (Page 18)

NIRCal 5.5 Software Manual
18 NIRCal 5.5 Manual, Version A

In case spectra breaking ranks, show clearly deviating Scores and Residuals (Graphics /
Spectra / Residuals), these spectra are real outlier and should be eliminated from the
calibration / validation.

In case there are big differences between the reference values and the predicted values, but
the Scores of the referring spectra do not have particular deviations with high probability, the
Outliers appear because of false reference value. The lab determination should be repeated.

Group of samples with systematically deviations: this effect can be seen from time to time
when samples are evaluated their reference values have been determined in laboratories not
using exactly the same reference methods. Here only an alignment of the reference methods
can help.

Significantly different results depending on the chosen classification of the samples into the
calibration and validation set: the number of used samples is too small, for instance because
of not considered, hidden properties.
Remedy: Selective completion of the master data set that all possible variations flow into the
calculation.
Application of a quantitative calibration and interpretation of the results
During the application of a quantitative calibration, the referring concentration values of the measured
spectrum are calculated according to equation [1] and indicated.
These calculations always lead to a result, even when performing faulty measurements. (e.g. sample
of completely different, not calibrated substance class). The calculation of the concentration is
therefore enlarged with two further checks:

the concentration values found must be within the original calibration range, a warning- and
action-limit can be adjusted as well.

make sure that the new measured spectrum matches the calibration spectra and that the
Residual is within the allowed limit. A warning appears, when the residual of the measured
spectra is bigger than the maximum allowed residual. Results of the spectra with Residual
outlier are not taken for the average calculation of multiple measurements.
1.2 Introduction to NIRCal
1.2.1 General
The work flow for typical NIR Application with Büchi NIRWare is:
1. Create an Application in NIRWare Application Designer for reference measurements
2. Data Acquisition Spectra collection with NIRWare Operator
NIR- Spectroscopy
3. Assign Property value to spectra with NIRWare Sample Manager
Spectra + Reference Analysis
4. Calibration build mathematical models with NIRCal 5
Correlation known Spectra <- -> Concentrations / Identity
5. Copy and modify the Application for routine measurements
6. Assign the created calibration to the routine application
7. Use the mathematical models/calibrations within an Application in the NIRWare Operator for
Predictions
unknown Spectra -> Concentrations / Identity
In case a calibration after the first trial is not delivering the correct results, the steps 3-7 should be
repeated, the calibration should be expanded with new samples and tested again.
All data (like spectra, property value, projects, calibrations, etc) are saved in the NIRWare Database.