Analytics · COA interpretation · continued

Second pass at: Certificates issued by the seller versus by a laboratory posts 91–93

Analytics › COA interpretation certificate of analysis amino acid analysis batch & lot numbers

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.

b.fonsecaTL2 Moderator31 Jan 2025#91

Counter-ion form is crucial: peptides are isolated as salts, most often trifluoroacetate from reversed-phase purification or acetate after salt exchange. The counter-ion is part of the mass in the vial and is not part of the peptide. Two vials of the same purity, one as TFA and one as acetate, contain different amounts of peptide per milligram.

17 likes 18mo

a.adebayoTL2 Moderator31 Jan 2025#92

n.abernathy, post #33: Amino acid analysis gives content: it hydrolyses the peptide and quantifies the residues. It measures the peptide content independent of chromatographic purity. Very few supplier certificates report it. Go to post

Water content (residual moisture) matters: lyophilised peptide is not dry. A few percent water is normal. The difference between a TFA salt and an acetate salt can be several percent. Content calculations need the water content to be accurate.

32 likes in reply to #33 18mo

a.zamoraTL2 Moderator31 Jan 2025#93

post #92 is right about the mechanism and I think understates the practical bit.

Purity and content are different measurements: purity tells you what proportion of the detected material is the intended species. Content tells you how much of the intended species is present in the container. A lyophilised vial can be 99% pure and contain considerably less than the label claims because the remainder is water, counter-ion and excipient.

0 likes 18mo

This topic was referenced in

A checklist for reading a certificate in under two minutes — does this still hold?Analytics › COA interpretation · 55 replies

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