Re: How to correct absorption spectrum of a fluorescent compound?

Marvin wrote:
> Farooq W wrote:
> > I came across a related problem (of academic interest) in Galen Ewing's
> > book on Instrumental Analysis.
> >
> > "The absorption spectrum of a fluorescent substance determined with a
> > coventional spectrophotometer is likely to be in error because of
> > fluorescence. Suppose a compound has an absorption maximum (hence an
> > excitation maximum) at 290 nm and a fluorescence maximum at 350 nm. At
> > what wavelength would you expect the greatest error. Would the observed
> > absorbance be too large or too small at this point. Would your answers
> > be different for a spectrophotometer in which the radiation from the
> > lamp passes through the cuvet before dispersion in the monochromator"
> >
> > I think the greatest error would be at 290 nm, where the absorbance
> > recorded would be too low because "extra" light due to excitation would
> > be reaching the detector.
> > For the second spectrophotometer which uses dipersion deivce between
> > sample and detector one would get the correct spectrum.
> >
> > Does anyone else has more practical suggestions for the correction of
> > such spectrum?
> >
> If you know the wavelength range of the fluorescence, you can insert a band-pass filter
> between the sample and the detector, to block the fluorescent wavelength. If the
> wavelength you are scanning reaches the fluorescent wavelength, you have to remove the
> bandpass filter.
>
> An instrument with monochromators on both sides of the sample, with the wavelengths
> synchronized, would be ideal. Not likely you have it.

Are such absorption spectrophotometers available? What are they called?

.

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