BUCHI NIRCal - Manual (Page 32)

NIRCal 5.5 Software Manual
32 NIRCal 5.5 Manual, Version A
NOTE
Loop 1 to Loop 3 represent the sequence for optimising a calibration. After each change in the
selection, the calculation and principal component selection should be repeated.
2.1.3 Selecting the Calibration Method
The calculation method can be selected in the Menubar: [Calibration / Method / CLU Cluster] or by
clicking the icon
2.1.4 Selecting the Calibration and Validation Spectra
Samples of known characteristics, both chemical and physical are used to generate qualitative
calibrations. For each substance classes 5-15 different batches should be used for the calibration. The
measured spectra are divided into two sets:

Calibration Spectra: spectra selected for the calibration: C-Set, about 2/3 of all measured
spectra, at least 3 spectra.
Generally, the calibration spectra should contain all “acceptable extreme information” to
define the limits of acceptance.

Validation Spectra: about 1/3 of all measured spectra selected for the validation V-Set at least
2 spectra. Only if a calibration treats the validation spectra equal to the calibration spectra, the
settings can be considered as OK.
NOTE
These two groups of spectra should be:

independent from each other;

no overlapping allowed.
Suggested selection: Blockwise: 6-3, if always 3 spectra per batch where measured. In case some
extreme samples are in the V-Set, see Loop 3.
It is possible to leave out some spectra from the C- and from the V-Set, these spectra are in the
Unused Set = U-Set:
C-Set + V-Set + U-Set = All Spectra
The U-Set is visible in the calibration results (see
Calibration Protocol ), but will not influence the
calibration and validation results e.g. will not be considered for the Q-Value calculation.
Link:
Spectra selection
2.1.5 Selecting the Calibration Wavelengths
The exact wavelength / wavenumber range measured is dictated by the instrument type used for the
spectrum measurement. The selected wavelength / wavenumber range depends on the application
and the measuring option used.
NOTE
In general the calibration wavelength / wavenumber range should be as wide as possible.
Suggested wavenumber range for NIRFlex N-500 with measuring options

Solids and Liquids: 4'000-10'000 cm
-1
;

Fiber Optics: 4'500-10'000 cm
-1
.

Solids with Tablet Accessory: 6'000-11'520 cm
-1
.
The calibration wavelengths define the spectrum range, where the mathematical algorithms PCA is
applied.