Melanin shows an absorption maxima only at far UV region nearly (180-190 nm).But many assays like Turrick et al 2009 describes the method that use 400 nm for melanin estimation.Why this 400 nm is used instead of 180 nm ?
One reason for not always using the absorbance maximum is to also consider what else absorbs in that range. The problem at 180-190 (actually almost anywhere shorter than 220 nm) is that pretty much everything biological absorbs in that range, and most labs do not have specs that can make decent measurements at that short wavelength. 400 may not be the max, but a number of other things (such as nucleic acids, carbs, salts, colorless proteins, etc) do not interfere in this range.
Hi Nobel
I think below mention link can solve your problem
The spectroscopy of human melanin pigmentation," by N. Kollias. In: Melanin: Its Role in Human Photoprotection, pp. 31 - 38. Valdenmar Publishing Co. (1995).
hi noble sir
hope this ll help u little
http://cebp.aacrjournals.org/content/7/3/203.long
One reason for not always using the absorbance maximum is to also consider what else absorbs in that range. The problem at 180-190 (actually almost anywhere shorter than 220 nm) is that pretty much everything biological absorbs in that range, and most labs do not have specs that can make decent measurements at that short wavelength. 400 may not be the max, but a number of other things (such as nucleic acids, carbs, salts, colorless proteins, etc) do not interfere in this range.
180 is Far UV. You need specialized setup to record absorption in this region (such as continuous flow of Nitrogen). Besides in that region any pi or n electron will be excited. Therefore, the absorption band in that region is not compound specific. Besides melanin absorption maximum is 335nm (http://www.cl.cam.ac.uk/~jgd1000/melanin.html) and it shows substantial absorption at 400nm as well.
Hi james
In my lab too it is difficult get reading on the far UV region as you have mentioned . I had only seen in papers melanin showing maxima at 180-190 range..Then also the Why remains..Why specifically 400 nm ?
Uttam
Thanks for suggesting that paper.I too have seen this type of spectrum for melanin in couple of other papers too..I don't pure melanin gives a maxima at 330nm .It may due to some other impurities.
Alok
The paper you have suggested sounds good.Some facts we can understand from it on the doubt which I have raised..
400nm wavelength used in the spectroscopic estimation of melanin concentration because 400-800 nm is visible range & one can visualize the color easily & one can use easily available colorimeter
Madhukar
Thank you first
During melanin research,most of the scientific people I go through usually ask this question .What is the absorption maxima of melanin ? From the above answers I can conclude melanin has no absorption maxima (specifically).and I can use 400nm as Turrick have done for my further estimations..
Thank you all...
180-190nm is not the wavelength for quantitation of melanin in any crude mixture. Here virtually, everything and anything can show the lambda max. This will give you wrong results. You can use this wavelengths if you have a highly purified sample of melanin. Therefore, 400nm is a better alternative but not the best.
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