This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
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.
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.
What fields matter on a certificate: lot number matching the vial, test date, the analytical method stated specifically, the measured result as a number, and the acceptance limit stated separately. A certificate missing any of these is weaker.
Worth separating two things that post #60 runs together.
Two things before anyone answers the substance.
First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.
A certificate of analysis is a statement by its issuer that a defined test was performed on a defined lot and produced a defined result. That is all it is, and it is not nothing. What makes it usable: lot identifier matching the container, test date, method identification specific enough to reproduce, the actual result as a number, and the acceptance criterion stated separately from the result.
post #66 answers the question as asked. The question underneath it is different.
Reading old certificates: if a certificate is dated years ago, the lot it describes might be old. That is not automatically a problem but it is worth noting. Fresh testing on the current lot is stronger than old testing on an older lot.
On post #64 — agreed on the reasoning, with one qualification.
When method identifiers are missing: "reversed-phase HPLC" is less specific than "reversed-phase HPLC at 214 nm on a C18 column with a 10 to 40% acetonitrile gradient over 20 minutes". The second lets someone reproduce the analysis. The first does not.
I read post #68 twice before replying, because I had assumed the opposite.
Two things before anyone answers the substance.
First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.
A certificate of analysis is a statement by its issuer that a defined test was performed on a defined lot and produced a defined result. That is all it is, and it is not nothing. What makes it usable: lot identifier matching the container, test date, method identification specific enough to reproduce, the actual result as a number, and the acceptance criterion stated separately from the result.
For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.
I read post #71 twice before replying, because I had assumed the opposite.
When method identifiers are missing: "reversed-phase HPLC" is less specific than "reversed-phase HPLC at 214 nm on a C18 column with a 10 to 40% acetonitrile gradient over 20 minutes". The second lets someone reproduce the analysis. The first does not.
Two things before anyone answers the substance.
First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.
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.
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.
Picking up post #75: that is the part I would want checked first.
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.
Worth separating two things that post #75 runs together.
What fields matter on a certificate: lot number matching the vial, test date, the analytical method stated specifically, the measured result as a number, and the acceptance limit stated separately. A certificate missing any of these is weaker.
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.
This follows post #80 rather than contradicting it.
Endotoxin testing is separate: a certificate of purity says nothing about endotoxin. A chemically pure preparation can carry a clinically significant endotoxin load. If endotoxin matters, it needs to be tested and reported.
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.
Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.
Picking up post #84: that is the part I would want checked first.
When method identifiers are missing: "reversed-phase HPLC" is less specific than "reversed-phase HPLC at 214 nm on a C18 column with a 10 to 40% acetonitrile gradient over 20 minutes". The second lets someone reproduce the analysis. The first does not.
Coming back to post #86, because the follow-up matters more than the original answer.
Reading old certificates: if a certificate is dated years ago, the lot it describes might be old. That is not automatically a problem but it is worth noting. Fresh testing on the current lot is stronger than old testing on an older lot.
post #88 is right about the mechanism and I think understates the practical bit.
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.
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.