I have to repeat an experiment a college that worked here a long time ago did. Only his documents are still available.
In the experiment he "simply" did determine the %-content of a powder by comparison with a reference standard based on dry mass.
He dried sample and reference to get loss on drying.
For the UV-Vis measurement he weight in the same ammount of the dried reference and the "wet" sample.
He solved both to about 10µg/1ml in destilled water and measured their absorbance at a single wavelength.
For calculating the %-content he used the formula:
Content (%) = Absorbance of sample / Absorbance of reference x
weight of reference / weight of sample (1- Loss on drying) x 100
I know try to understand where he got this formula/what it is based on to understand what he did - as my results from my first approaches differ significant. He did the experiment in a cooperation - and his results are verified by others/right. But as i said: it was some time ago (1990s) and no one is here that i could ask - so i have to work with the papers i got.
To my knowledge the "only/normal" way to get results for an unknown substance when there is a reference available is to create a calibration curve by solving the reference standard in different concentrations.
Does the formula/approach look familiar to anyone? I am still quite new to UVVis - and this seems to be above my current level.
Dear Daryl,
you can divide the formula in 2 parts. The first one is Absorbance of sample(As)/Absorbance of reference(Ar). If As = Ar the concentration of the sample is the same as the reference material, if As/Ar = 0,5 concentration of sample is half and so one. This is the same you do in a calibration. The second part is weight of reference(wr)/weight of sample(1-loss on drying)*100 is to adjust the weights on a dry base. This is needed because the reference material is used dried whereas the sample is wet. If the sample is completly dry and you use a identical wheight for sample and reference the second term is "1" and thus meaningless.
However, the results is not % content, but % content relative to the reference. If your reference is the pure substance this is identical to % content. What your colleague did is as simple kind of one point calibration.
Kind regards
Dieter
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Powders