Subject: Re: CCL:solvent cutoff wavelength

From: Bruce Allan Palfey <[email-masked]>
Date: Sun, 20 Oct 2002 19:29:04 -0400 (EDT)

Tarek

The problem with measuring the absorbance in a region where the solvent
absorbs is that very little light makes it to the instrument's detector,
even for the blank.  Thus you would be trying to detect the difference
between the very low light intensity for your reference and an even lower
intensity for the sample plus solvent.  In practice, most instruments
allow enough stray light to reach the detector to make the measurement
you're describing suspect at best.  Therefore, the solvent blank does not
assure a meaningful result, and subtracting the spectrum of the solvent
> from the spectrum of the solution is not likely to help.  Adherence to
Beer's law (the linearity of absorbance with concentration) would perhaps
suggest that your results are meaningful.

ciao,
Bruce

Bruce Palfey
Department of Biological Chemistry
University of Michigan
Ann Arbor, MI 48109-0606

On Fri, 18 Oct 2002, Tarek Mamoun El-Gogary wrote:

> Dear CCL members,
> I am sorry to post this general question.
> I am using a double beam spectrophotometer to measure the electronic
> absorption spectra of some organic compounds, so I am using the solvent as a
> blank and run autozeroing before scanning the sample. My question is: should
> I stop scanning at the cutoff wavelength (240 nm) of the solvent or may I
> measure the samble beyond the cutoff wavelength of the solvent? As the
> solvent is in the blank cell so its interference will be eliminated, is that
> correct?
> regards
> Tarek
>
>
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