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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 you have 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 D
The short wavelength radiation leading to photodegradation comes from
the light of the D
wavelengths above 400 nm, the D
intensity supplied by the Tungsten lamp is sufficient for a good signal to
noise ratio over the wavelength range 400 nm - 1100 nm.When using cells
with small apertures, check the signal to noise ratio by making sample
measurements under conditions of your application.
Stirring and Temperature Control
Solution homogeneity can be a problem, especially for viscous solutions.
There are cases where, due to convection induced gradients, rapid
absorbance changes may give irreproducible data. These changes can be
observed spectroscopically by taking measurements with short integration
times. To minimize convection effects keep the temperature of your sample
the same as the cell holder or environmental temperature. Problems like
these can also be minimized by using a thermostattable cell holder and/or
a stirring module.
Agilent Cary 8454 UV-Visible Spectroscopy System Installation Guide
-Lamp off
2
- Lamp. For application where readings are taken at
2
Good Measurement Practices
General Considerations
- Lamp can be turned off. The light
2
3
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Troubleshooting
