January 17, 2022, 07:29:18 PM
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Topic: Absorbance Wavelength  (Read 346 times)

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Offline KanizRonakSultana

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Absorbance Wavelength
« on: January 07, 2022, 11:58:43 PM »
Wondering, if anybody could help me out to find the absorbance wavelength of pure Vegetable Glycerin?
Thanks in advance.

Offline Borek

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Re: Absorbance Wavelength
« Reply #1 on: January 08, 2022, 03:39:28 AM »
Standard procedure is to record the spectra and choose whichever wavelength suits your needs best.
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Offline Orcio_87

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Re: Absorbance Wavelength
« Reply #2 on: January 08, 2022, 05:26:26 AM »
For a quantitative measure, the best wavelength is the one which gives the highest absorbance.. if there no other compounds in the sample absorbs at the same wavelenght.

Offline morphism

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Re: Absorbance Wavelength
« Reply #3 on: January 08, 2022, 08:43:14 AM »
First of all, you should get the pure Vegetable Glycerin's spectra and after that use some software or any manuals/procedures "absorbance - frequency". It should be clear, my friend.

Online Babcock_Hall

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Re: Absorbance Wavelength
« Reply #4 on: January 08, 2022, 09:09:04 AM »
Why do you need to do absorption spectrophotometry on glycerin?  What are you trying to accomplish?

Offline rjb

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Re: Absorbance Wavelength
« Reply #5 on: January 09, 2022, 05:52:31 AM »
Just to check, but are we discussing UV-Vis here or something else?

If we are considering UV-Vis, then generally speaking (as Borek stated), lambda max is best determined empirically; presumably you have access to a UV-Vis setup.

That said, I think you're going to struggle as (to the best of my recollection) Glycerin does not absorb in the visible or UV regions which is why it can be used as as solvent above about 230nm.

R
« Last Edit: January 09, 2022, 06:30:22 AM by rjb »

Offline Corribus

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Re: Absorbance Wavelength
« Reply #6 on: January 10, 2022, 11:22:37 AM »
For a quantitative measure, the best wavelength is the one which gives the highest absorbance.
This is not always the case. For UV-Visible spectroscopy, optimal wavelength selection depends on a lot of factors, including the instrument being used, but generally speaking it would be the wavelength at which absorption over the concentration range of interest is between (approximately, depending on instrument) 0.1-1.0 OD. If the molar extinction coefficient is too high at the chosen wavelength, then for certain concentrations of the analyte the absorption will exceed OD values where the measurement becomes less accurate due to reliable instrumental light sensitivity. Sample dilution or using cuvettes with different geometry are options in this case, but the easiest option is frequently just to use a wavelength with lower absorptivity.

There are other situations where the optimal wavelength is not the one where absorptivity is highest. The wavelength should be chosen after careful consideration of the sample/solvent system, specific experimental needs, and instrument limitations.

If the OP is referring to UV-Visible absorption of glycerine, based on comparison to ethanol I would expected no appreciable absorption at wavelengths above 250 nm. We might expect to see some weak absorption by pure glycerine at wavelengths deeper into the UV. Depending on how pure it is, glycerine may also have some contaminants (aldehydes, natural pigments etc.) that absorb weakly in the UV region, so be careful of that. Without more information on what the OP is doing, particularly the wavelength region the OP is interested in, it's impossible to provide further guidance.
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