Analytics · COA interpretation

A field-by-field walk through a certificate of analysis

Analytics › COA interpretation documentation quality amino acid analysis certificate of analysis batch & lot numbers reference standards

Solved

Solved by NLoughran in post #3

Peptide content and chromatographic purity are separate determinations and a certificate that reports only one has answered only one question. Content is the one that tells you how much is in the vial.

Jump to the accepted answer →

ambient_reviewTL3Regular13 Jul 2025#1

Posting this under the heading it deserves: A field-by-field walk through a certificate of analysis Everything below is what sits behind that.

I have spent a fortnight trying to pin field-by-field walk through a certificate down and I want to set out where I have got to, because I suspect the honest answer is duller than the thread this will produce.

What I have: a consistent observation across a small number of cases, collected the same way each time. What I do not have: any controlled comparison, or any reason to think my cases are representative.

The specific question is whether the pattern survives once the obvious confounder is removed. I cannot remove it with what I have.

27 likes 13mo

v.malinowskiTL213 Jul 2025#2

On the opening post — agreed on the reasoning, with one qualification.

The most useful thing anyone has posted about field-by-field walk through a certificate in this category was a table of what had been measured and by whom. That is what I would want again.

29 likes 13mo

NLoughranTL3Regular Solution13 Jul 2025#3

Peptide content and chromatographic purity are separate determinations and a certificate that reports only one has answered only one question. Content is the one that tells you how much is in the vial.

7 likes 12mo

k.karlsenTL213 Jul 2025#4

"Not less than 98 per cent" is a specification. "98.3 per cent" is a result. A certificate carrying only the first has not told you what was measured.

The step people skip is the one I have spelled out.

5 likes 12mo

h.nicolaidesTL3Regular14 Jul 2025#5

v.malinowski, post #2: On the opening post — agreed on the reasoning, with one qualification. The most useful thing anyone has posted about field-by-field walk through a certificate in this category was a table of what had been measured and by whom. That is what I would want again. Go to post

Two claims get bundled together under field-by-field walk through a certificate and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.

Almost every disagreement in threads like this one dissolves once you say which of the two you are making.

10 likes in reply to #2 12mo

p.onwukaTL214 Jul 2025#6

NLoughran, post #3: Peptide content and chromatographic purity are separate determinations and a certificate that reports only one has answered only one question. Content is the one that tells you how much is in the vial. Go to post

Worth separating two things that post #2 runs together.

I changed my mind about field-by-field walk through a certificate after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.

22 likes in reply to #3 12mo

l.aaltonenTL314 Jul 2025#7

Collapsed as off-topic by two members at trust level 3 or above

Post #4 is right about the mechanism and I think understates the practical bit.

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.

so.mbekiTL214 Jul 2025 · edited#8

No notes. Posting so the count is not one.

3 likes 12mo

WickramasingheTL2Member14 Jul 2025#9

p.onwuka, post #6: Worth separating two things that post #2 runs together. I changed my mind about field-by-field walk through a certificate after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens. Go to post

Adding a data point of agreement rather than a data point.

28 likes in reply to #6 12mo

w.moreauTL214 Jul 2025#10

so.mbeki, post #8: No notes. Posting so the count is not one. Go to post

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.

That is the honest state of it as of this week.

0 likes in reply to #8 12mo

c.wijnbergTL214 Jul 2025#11

Collapsed as off-topic by two members at trust level 3 or above

Agreed on field-by-field walk through a certificate, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.

da.bakkerTL214 Jul 2025#12

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.

Filing this under things that are true until someone shows me otherwise.

9 likes in reply to #6 12mo

cannula_traceTL3Regular14 Jul 2025#13

On post #10 — agreed on the reasoning, with one qualification.

Two people in this thread mean different things by field-by-field walk through a certificate and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.

2 likes 12mo

j.restrepoTL214 Jul 2025#14

Picking up post #13: that is the part I would want checked first.

A methods point on field-by-field walk through a certificate rather than a substantive one: if the comparison is not like for like, the difference you are measuring is the difference in method.

0 likes 12mo

footnote_entryTL3Regular14 Jul 2025#15

Coming back to post #13, because the follow-up matters more than the original answer.

A chromatogram supplied as a small image is legible for peak shape and not for baseline detail. That is enough to sanity-check an integration and not enough to reproduce it.

If this contradicts something upthread, the upthread version may well be the better one.

14 likes 12mo

k.kuuselaTL214 Jul 2025 · edited#16

The version of field-by-field walk through a certificate that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.

5 likes 12mo

n.rowntreeTL3Regular14 Jul 2025#17

Asking for the batch record rather than the certificate is a reasonable request and the response to it is informative whichever way it goes.

0 likes in reply to #3 12mo

r.bakkenTL214 Jul 2025#18

This follows post #17 rather than contradicting it.

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.

0 likes 12mo

IsaksenTL3Regular14 Jul 2025 · edited#19

Post #17 put the caveat in the right place and I want to underline it.

The failure mode on field-by-field walk through a certificate is boring rather than dramatic. It is almost always the step everyone assumes was done correctly because it is too simple to get wrong.

9 likes 12mo

t.ibarraTL214 Jul 2025#20

Collapsed as off-topic by two members at trust level 3 or above

Appreciated. The plain phrasing does more work here than a longer post would.

ZieglerTL3Regular14 Jul 2025#21

Isaksen, post #19: Post #17 put the caveat in the right place and I want to underline it. The failure mode on field-by-field walk through a certificate is boring rather than dramatic. It is almost always the step everyone assumes was done correctly because it is too simple to get wrong. Go to post

Field-by-field walk through a certificate is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.

0 likes in reply to #19 12mo

g.verhoevenTL214 Jul 2025#22

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.

0 likes 12mo

diluent_watchTL2Member14 Jul 2025#23

An itemised related-substances table with retention times says considerably more about the synthesis than a single total. A total tells you how much is not the main peak and nothing about what it is.

9 likes 12mo

m.dumitruTL214 Jul 2025#24

Quietly grateful for the plain phrasing. Not every thread gets that.

21 likes 12mo

glossary_lineTL1Member14 Jul 2025#25

Post #22 is right about the mechanism and I think understates the practical bit.

A certificate 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.

I am confident about the direction and much less about the magnitude.

29 likes 12mo

z.vogelTL214 Jul 2025#26

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.

If that is already documented somewhere, ignore me and link it.

0 likes 12mo

h.nicolaidesTL3Regular15 Jul 2025#27

The most useful reply I ever got about field-by-field walk through a certificate was a request to state my units. It sounds like pedantry and it has saved me twice.

5 likes 12mo

ca.vermeulenTL215 Jul 2025#28

k.kuusela, post #16: The version of field-by-field walk through a certificate that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live. Go to post

The distinction between release testing and characterisation is one industrial documents make and retail ones usually do not. It is the difference between "we tested every lot for this" and "we established this once".

14 likes in reply to #16 12mo

r.villalobosTL215 Jul 2025#29

k.karlsen, post #4: "Not less than 98 per cent" is a specification. "98.3 per cent" is a result. A certificate carrying only the first has not told you what was measured. The step people skip is the one I have spelled out. Go to post

Post #26 answers the question as asked. The question underneath it is different.

I have no financial interest in anything named in this thread and I want to say so before I comment on field-by-field walk through a certificate, because it is the sort of subject where it matters.

0 likes in reply to #4 12mo

r.danquahTL215 Jul 2025#30

w.moreau, post #10: 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. That is the honest state of it as of this week. Go to post

I read post #28 twice before replying, because I had assumed the opposite.

Practical answer on field-by-field walk through a certificate, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.

5 likes in reply to #10 12mo

Sponsored Janoshik Analytical — independent third-party testingHPLC purity and mass-spectrometric identity on submitted samples, reported with the method stated. The laboratory most often cited in this community’s verification records.Independent testing → Sponsored GL Biochem (Shanghai) Ltd. — synthesis, directFounded 1998. ISO 9001 and cGMP certified, over 1,500 staff and 200-plus patents. Custom peptide synthesis and amino acid derivatives, with a batch certificate on every order.Custom synthesis →