I want to do the standard curve for quercetin that will be used in total flavonoid content test. However, what I have currently is isoquercetin. Can it be used?
Thank you ;-)
These compounds have different moleculat weight. I think you may use it taking into account that isoquercetin has different absorbance pattern in UV-Vis spectrum in respect to quercetin so you should read the absorbance at the correct wave length. Then you may report the results also in quercetin equivalent taking into account the difference in molecular weight between these compounds.
Although Alessandro is right, you don't have the standard of quercetin in hand, which is your problem. However, based on the structure of them, the super conjugated structure of them are exactly the same. I am sure they will have almost the same the same UV-vis spectrum. (Similar example: Methylparaben and propylparaben have the same UV-vis spectum). Since they have different molecular weights, you need to use mol/L instead of g/L as the concentration unit when you get the calibration curve.
The lambda max of quercetin is 369 nm, and for isoquercetin is 352.6 nm.
These compounds have also different solubility since one is a glycoside and should be more soluble in polar solvents.
It is very interesting, since shifting of 13 nm is very significant. If I have these two chemicals, I will do the experiments by myself. I just search the internet to see any useful information about them. (1) There are three lambda max located at around 200 nm, 250 nm, and 370 nm for both of them. (2) For isoquercetin, it is 365 nm instead of 352.6 nm (see Figure 3 in paper 1 attached). I only saw 352.6 nm from the wikipedia which don't provide any reference. The same wavelength of 365 nm in Figure 3 of Paper 2. (3) I didn't see the whole spectrum of them. However, I found some very useful information in Figure 7 of Paper 3 to support my assumption. You can see the spectrum are the same between Quercetin and isohamnetin. Unfortunately, they didn't provide isoquercetin. In the end, I don't suggest Afifah to use isoquercetin to make the calibration curve for quercetin, if you want to publish a peer reviewed article. However, if you only need to know the approximate concentration of quercetin, then you can either use this way or use the molar extinction coefficient of quercetin from others' work.
Thank you Allesandro and Hongzhu for the answers. Really appreciate the efforts. Will use the information and read the attached references :-)
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