Photosensitive Samples - Agilent Technologies Cary 8454 Operator's Manual

Good Measurement Practices 4
General Considerations

Photosensitive Samples

A few substances are very photosensitive. They degrade or undergo
photochemical reactions if exposed to light. This can be easily seen by a
decrease of sample absorbance over time.
Use of Filters
The shorter wavelength, higher-energy UV light is most likely to degrade
photosensitive samples. If this is a problem, you can selectively block portions
of the UV spectrum with a UV cut-off filter. An optical filter wheel assembly
with three cut-off filters is available for the spectrophotometer. The cut-off
wavelength of the filter you choose should be low enough that it does not
eliminate important spectral information, but high enough that it blocks the
light that could degrade your sample. If you use a filter with your samples, you
must use the same filter when you make your blank measurement.
Turning the D2-Lamp off
The short wavelength radiation leading to photodegradation comes from the
light of the D2-lamp. For application where readings are taken at wavelengths
above 400 nm, the D2-lamp can be turned off. The light intensity supplied by
the Tungsten lamp is sufficient for a good signal to noise ratio over the
wavelength range 400–1100 nm. When using cells with small apertures, you
should check the signal to noise ratio by making sample measurements under
the conditions of your application.
Agilent Cary 8454 UV-Visible Spectroscopy System Operator's Manual 61