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B. Igne et al.
12.3.7.1 Referencing
One potential difference between method development and method use is the requirement for referencing the spectrometer. Off-line or at-line methods will usually call
for referencing either before each sample (this is very common when the reference
standards are built in the instrument) or at a set frequency that has been proven
to sustain method performance. However, for on-line or in-line deployments, other
considerations are at play. If the instrument is located in a manufacturing suite or
technical space and these environments are expected to change in thermal conditions during use, the stability of the lamps and detectors may be affected. In such
case, the referencing of the instrument (white reference (e.g., 99% reflectance standard) and potentially dark reference) may be required more frequently. The chosen
rate/periodicity should ensure suitable spectrometer performance.
For in-line applications, it may not be possible to remove and clean the probe
for referencing. Off-the-shelf commercial systems allow for the probe to be automatically removed from the process, cleaned and referenced. In addition, probes and
spectrometer systems are commercially available with built-in referencing that allows
the system to avoid drifts for extended periods of use (several days). But regardless
of how the referencing is performed, it must be done at a relevant frequency to ensure
that any change in the analytical system is accommodated for.
12.3.7.2 System Suitability
Turning on a spectrometer, letting it warm up, and collecting a reference should not
be the only actions performed prior to use. Instruments usually follow a scheduled
performance qualification program either completed by the vendor or the user, but
these could be completed once a year or once every few months. Additional tests are
necessary prior to use and during use to confirm that the instrument and sampling
system are performing as intended when compared against acceptance criteria and
these should be trended against historical values. These tests, often called system
suitability tests or on-going performance verifications, will often use traceable standards to confirm that the equipment is meeting acceptance criteria and can be used to
generate data as per the method procedure. System suitability is specifically discussed
in guidelines and standards [7, 20].
12.3.7.3 Method Performance Monitoring
With chromatographic methods, it is typical to run a known working standard reference sample before and periodically throughout a sample set run to confirm that, over
the duration of the run, the system performed as intended. In addition, these measurements are used to generate the model calibration curve at the time of use. However,
as described earlier, typical NIR methods rely on a priori established calibration
curves, and future samples will be projected onto that model. To ensure that the
B. Igne et al.
12.3.7.1 Referencing
One potential difference between method development and method use is the requirement for referencing the spectrometer. Off-line or at-line methods will usually call
for referencing either before each sample (this is very common when the reference
standards are built in the instrument) or at a set frequency that has been proven
to sustain method performance. However, for on-line or in-line deployments, other
considerations are at play. If the instrument is located in a manufacturing suite or
technical space and these environments are expected to change in thermal conditions during use, the stability of the lamps and detectors may be affected. In such
case, the referencing of the instrument (white reference (e.g., 99% reflectance standard) and potentially dark reference) may be required more frequently. The chosen
rate/periodicity should ensure suitable spectrometer performance.
For in-line applications, it may not be possible to remove and clean the probe
for referencing. Off-the-shelf commercial systems allow for the probe to be automatically removed from the process, cleaned and referenced. In addition, probes and
spectrometer systems are commercially available with built-in referencing that allows
the system to avoid drifts for extended periods of use (several days). But regardless
of how the referencing is performed, it must be done at a relevant frequency to ensure
that any change in the analytical system is accommodated for.
12.3.7.2 System Suitability
Turning on a spectrometer, letting it warm up, and collecting a reference should not
be the only actions performed prior to use. Instruments usually follow a scheduled
performance qualification program either completed by the vendor or the user, but
these could be completed once a year or once every few months. Additional tests are
necessary prior to use and during use to confirm that the instrument and sampling
system are performing as intended when compared against acceptance criteria and
these should be trended against historical values. These tests, often called system
suitability tests or on-going performance verifications, will often use traceable standards to confirm that the equipment is meeting acceptance criteria and can be used to
generate data as per the method procedure. System suitability is specifically discussed
in guidelines and standards [7, 20].
12.3.7.3 Method Performance Monitoring
With chromatographic methods, it is typical to run a known working standard reference sample before and periodically throughout a sample set run to confirm that, over
the duration of the run, the system performed as intended. In addition, these measurements are used to generate the model calibration curve at the time of use. However,
as described earlier, typical NIR methods rely on a priori established calibration
curves, and future samples will be projected onto that model. To ensure that the