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I have several peptides (20-50 amino acids long) which I want to quantify the solubility/concentration in a solvent at certain temperature and pH.

These peptides may or may not contain Tryptophan or Tyrosine (aromatic residues) in them. What's the preferred quantification method for it?

I came to UV-Vis method (e.g. NanoDrop) and Fluorescence method (e.g. Qubit). Do those methods strictly require the presence of Tryptophan or Tyrosine?

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    $\begingroup$ Do you have a spectrophotometer or fluorimeter or both? If you have only one or the other than you have no choice if both measuring fluorescence is generally more sensitive than measuring absorbance. $\endgroup$
    – porphyrin
    Commented Apr 26, 2022 at 8:48
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    $\begingroup$ @porphyrin I have both. Does fluorescence require aromatic residues? Nanodrop-UV seems to require aromatic. $\endgroup$
    – littleworth
    Commented Apr 26, 2022 at 8:51
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    $\begingroup$ What about phenylalanine? Do you have it in your peptides? And do you have an approximate idea of the concentrations to be expected? Of course there are the typical assays for protein quantification (Bradford, BCA...) which you could use. $\endgroup$
    – Snijderfrey
    Commented Apr 26, 2022 at 10:34
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    $\begingroup$ Expensive methods: Mass Spec or FT-IR. $\endgroup$
    – Karsten ♦
    Commented Apr 26, 2022 at 11:41
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    $\begingroup$ Generally yes, fluorescence requires aromatic residues, you should excite from 300 to 310 nm approx to excite tryptophan and not phenylalanine or tyrosine. Detection should be at about 380 nm to see just trp but you should look up details of spectra. It will be hard to tell if your protein contains several trp or just one as the environment changes the fluorescence yield. You may need to do absorption as well. $\endgroup$
    – porphyrin
    Commented Apr 26, 2022 at 15:25

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