Metrohm NIRS XDS MultiVial Analyzer - Manual (Page 72)

70 ▪▪▪▪▪▪▪
Information about the wavelength standard:
The wavelength standard used is directly traceable to NIST SRM-1920a, through direct comparison
on the Metrohm master reflectance instrument, and in chemical formulation. In addition to the
prescribed formulation, one additional ingredient is added, in a small amount, to provide peaks
beyond those normally found in SRM-1920a. This material has very sharp bands, which are found to
be stable and repeatable.
Spectra of each are as described:
The darker spectrum, which has no discernible peaks beyond about 2150nm, is SRM-1920a.
The FOSS WSR Wavelength Standard is the lighter spectrum, and has clear peaks visible at above
2200nm. These additional peaks are used to set the wavelength scale of the instrument to aid in
instrument matching. This is one important step in method transfer.
The Foss WSR Wavelength Standard exhibits slightly different absorbance and baseline levels, due to
the reflectivity of the added ingredient. The peaks, however, are in the same wavelength positions,
and are similar in shape to SRM-1920a.
The XDS instrument is set to NIST nominals during Instrument Calibration, since these are the best
known information for NIR peak wavelengths. Peaks for the additional ingredient are set to peak
nominals determined by measurement on several different types of research instrumentation.
In Wavelength Certification, the NIST-stated uncertainty of 1.0nm is applied. Tighter tolerances are
not appropriate, unless NIST revises the stated uncertainty of SRM-1920a at some point in the future.