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New SRMS for Near Infrared and Raman Spectroscopy
Abstract:
Standard Reference Materials (SRMs) 2241 and 2036 are a
newly introduced Raman intensity standard and diffuse reflectance
near-infrared wavelength standard. These standards were
developed to correct a samples’ spectrum for instrument
response and to validate the performance of the spectrometer.
These standards are primarily intended for use by the pharmaceutical
community and other industries that require traceabilitiy.
These new standards enable the calibration of these spectrometers
at a fraction of the cost of current methods and resolve
several technical issues with an existing SRM. The use of
these standards will enable the development of standardized
Raman spectral libraries, instrument–to-instrument comparisons,
and transfer of calibration methods between labs and instruments.
Purpose:
To provide users of Raman and NIR instrumentation a set
of performance validation standards.
Major
Accomplishment: No standardized Raman libraries exist
because of the lack of adequate calibration methods and
standards. To this date, Raman spectra are instrument dependent
and a convolution of the spectrometer instrument response
and scattering characteristics of the sample. The series
of SRM 224x standards is intended to largely solve this
problem. These are glasses that luminesce when irradiated
with the spectrometers’ laser. The shape of this luminescence
is certified by NIST and is described by a simple polynomial
expression. This polynomial, together with a measurement
of the luminescence spectrum of the SRM, can be used to
determine the spectral response correction that is unique
to each instrument. This will enable the correction of a
sample Raman spectrum so that it is system independent.
SRM
2241 -- "Raman intensity correction standard for systems
operating with 785 nm excitation"-- was certified this year.
SRM
2036 is a newly introduced NIR diffuse reflectance wavelength
standard. This standard provides the same level of calibration
confidence as NIST’s existing SRM 1920a but is easier to
produce, utilizes the same materials as SRM
2035 and SRM
2065, and eliminates the strong dependence of band position
on the resolution of the instrument that is inherent in
the use of SRM
1920a.
Impact:
The introduction of SRM 2241 and the next set of glasses
for 532 nm, 488-514 nm and 1064 nm Raman excitation sources
will enable the use of this technique in industries that
are regulated by the FDA. The lack of performance validation
and system correction standards has inhibited this technique
from being widely used in the pharmaceutical, chemical,
and forensics community.
The
introduction of SRM 2036, "NIR Reflectance standard," will
enable the calibration of a number of common sampling accessories
currently in use by the pharmaceutical industry. As SRM
1920a is no longer available it will replace this routinely
requested SRM.
Future
Plans: We are currently developing five additional glasses
that will be used for laser excitation frequencies between
488nm and 1064 nm. This suite of glasses will provide the
basis for developing system independent Raman libraries.
Future
plans for our NIR standards work include further work to
reduce the band location uncertainties of SRM 2036, the
incorporation of an internal reference for this sample,
and a transition plan to help secondary standard vendors
produce this SRM as well as the 2035/2065 series NIR wavelength
standards.
Contact:
Steven Choquette |
