Metrohm Vision – Diagnostics - Manual (Page 42)

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11
Photometric Test
Photometric Test provides a method to verify ongoing photometric performance of the instrument.
This is a requirement for pharmaceutical users. Before the Photometric Test can be run, a file must be
established using IPV Setup, described fully in the next section (D-54).
The IPV Setup file is acquired when the instrument is known to be operating properly, such as at
installation, or immediately after service. It is automatically stored in the C:\Vision directory with a file
name RSSVxxxx.da for reflectance standards.
Click on Diagnostics, IPV Setup to create an initial file for comparison. If more than one module is
used with a monochromator, IPV Setup must be done for each module, and a separate RSVxxxx file
created.
The test uses the same standards used in IPV Setup. Photometric Test compares current spectra of
each standard to those stored during IPV Setup. If any differences exceed normal tolerance values,
the instrument can be assumed to have changed in some manner, and may need service. This
method of instrument photometric testing is one means to demonstrate that the instrument is “in
control” from a regulatory standpoint.
Because the calibrated photometric standards are the link to previous photometric performance, the
standards should always be stored in their wooden box, and protected from fingerprints, dropping,
or other damage. If any cup is opened, dropped, or otherwise altered, Photometric Test results may
fail.
Photometric Test results are stored in the Diagnostic Database, and may be accessed at any time.
Control charts are plotted (after several tests have been stored) to provide an ongoing record of
performance.
During the test, the standards are checked at wavelengths where the response of the standards is
very flat, to eliminate the effect of minor spectral character on the measurement. The regions used
give a good overall picture of instrument performance and repeatability.
Acceptance tolerances are applied based on the type of instrument and sampling system. As long as
the instrument responds within the allowable range, it is assumed to be operating correctly on the
absorbance scale. If the instrument fails the test, the user should investigate the cause, and should
consider requesting a service call on the instrument.
NIRStandards are manufactured from a very stable material, and are certified on the Metrohm master
instrument, calibrated using procedures and materials traceable to the National Institute of Standards
and Technology (NIST) in the US. Each set of standards comes with a certificate of calibration, and
must be recalibrated once per year to assure consistent response, and to verify that no damage has
occurred that could alter the response of the standards. A wavelength standard, for use in
Wavelength Certification, is also included in the set.