Metrohm NIRS XDS MasterLab Analyzer - Manual (Page 78)

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If Wavelength Linearization fails for any reason,
check these items:
• Tablet Transmission Detector in correct
position
• Tablet Transmission Reference in
position on the sample carriage
• Aperture in place
• Instrument cover closed during scanning
If any of these items needs correction, please
set it properly and continue with the test.
7.1.2 Reference Standardization, Tablet Transmission
Reference Standardization is a method to provide a virtual 100% transmittance (transmission)
reference at each data point, to serve as a true spectroscopic reference with no character attributable
to the physical reference used. This is important to achieve a high-quality spectrum on each
instrument, and to enhance transferability between instruments.
The instrument reference (in tablet transmission) is diffusely transmissive, to closely duplicate the
scattering characteristics of tablets. This reference is just under 2 Absorbance Unit (AU) in
absorbance, which should be similar to the lowest absorbance tablets used in the instrument.
Because each reference is slightly different from others, each one is calibrated to the level of
transmittance value. This calibration is performed against a similar standard in the Transmission
Standards Set. (The calibration for that standard is contained on a mini-CD that is shipped with each
standard set.)
The standardization of the instrument transmission reference is performed using Reference
Standardization within Vision. Vision measures the absorbance of the instrument reference (at 0.5nm
intervals) and compares this to a calibrated photometric standard in the Transmission Standard Set. A
difference correction is computed. A second correction, between the calibrated standard, and 0
absorbance (100% transmission) is also stored.
When sample scans are performed on the instrument (in transmission) this correction is applied. The
newt result is that the sample scan is plotted on a true scale of absorbance, starting at 0 AU, and
extending up to the detection limits of the instrument.
The MasterLab Analyzer, when used in tablet transmission mode, has only one Reference
Standardization applied. Vision software stores the Reference Standardization files, which are
downloaded to the instrument, and are applied as a correction to each spectrum. Follow these steps
to create a reference standard:
Select Diagnostics,
Reference Standard,
Create Reference Standard.