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I have three chromatograms of the same eluted protein but at different concentrations, since it got diluted during purification process) and hence peak maximums at very different absorbances.

The highest is around 100 AU and lowest 20 AU. I want to present these and look at the difference in peak shape (because I want to look at aggregation). Can I simply multiply the data that generated the peak max at 20 AU by 5? Because then it is easier to compare the shapes of the peaks when they overlay each other.

Is this something one would do or is it totally forbidden?

Thanks in advice.

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    $\begingroup$ 1 kilogram times 5 is 5 kilograms, which is a totally different thing. But 1 arbitrary unit times 5 is another arbitrary unit, which is pretty much the same thing. $\endgroup$ Aug 14, 2019 at 21:04
  • $\begingroup$ Where readings such as absorbance 120 (AU) come from? There is nothing arbitrary in absorbance which is a well defined quantity withno units per se. $\endgroup$
    – Alchimista
    Aug 15, 2019 at 8:35

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I assume you have a UV/Vis absorbance based measurement. Then the absorbance should follow Beer´s Law which states that absorbance is proportional to concentration. Therefore you should be fine with your normalization approach. You could check if you are in the linear range by performing a calibration.

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    $\begingroup$ Strictly speaking: the fact that data are from UV/Vis measurements doesn't imply that the samples obey Beer law. Moreover absorbance is the peak integral not the height. Checking linearity could be done by diluting the samples but it is not inherent to the question nor necessary. All that is required is comparing shapes, and this is easier at the same scale and can be done. What could be the actual shape of one of the two features at a different concentration is right matter for discussion. And it seems what the OP want to do. $\endgroup$
    – Alchimista
    Aug 15, 2019 at 8:48
  • $\begingroup$ Agree. But linearity is absolutely necessary in order to be able to compare peak shapes directly because otherwise the shape depends also on the peak witdth. $\endgroup$ Aug 15, 2019 at 15:13
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You can conveniently normalize the peak height to unity, if your sole purpose is to compare the peak shapes. It is not forbidden at all. However you should not attempt any quantitation.

You can read the paper here Total peak shape analysis: detection and quantitation of concurrent fronting, tailing, and their effect on asymmetry measurements

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