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c/coa·posted 1 year ago by u/reflux_report

[PSA] area percent is not what most of this community thinks it is

Question

area percent is not what most of this community thinks it is. If you already knew this, the post is not for you and you can scroll on.

Net peptide content is the fraction of the powder that is actually peptide once counterion, water and residual solvent are accounted for. A 99% pure acetate salt can still be about 85% peptide by mass.

Related substances itemised individually is a much stronger document than a single total, because it tells you the shape of the impurity profile rather than its size.

UV at 214nm sees the peptide bond and picks up almost everything; at 280nm you are looking at aromatics only. Which wavelength the number came from is part of the number.

Tell me where this is wrong. That is the useful part of posting it.

0 up / 0 down47% upvoted4 commentsid 10ivak29 Apr 2025

4 comments

4 in this archive, depth 4

best — the order this archive was captured in

u/dead_space_doug1 point·1 year ago

Area percent is the peak area of your compound over the total integrated area, at one wavelength, on one gradient. It is a relative measure of what the detector saw, not a mass fraction of the vial.

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u/milos_trevino-5 points·1 year ago

That is not what the method line says. It names the technique; it does not certify the operator.

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u/anecdata_annie1 point·1 year ago

Pushing back a little: a missing field is usually presentation, not concealment. Ask for the full document before drawing conclusions.

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u/tuva_aalto1 point·1 year ago·edited

water content is on there and everyone skips it

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About c/coa

How to read a certificate of analysis and what it does and does not tell you. Area% versus mass%, identity versus quantity, water content, related substances, acetate counterions, and the difference between a vendor-supplied COA and an independent test on the vial you actually received.

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