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Analytics · COA interpretation

A checklist for reading a certificate in under two minutes

Analytics › COA interpretationcertificate of analysis batch & lot numbers amino acid analysis
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Solved by m.strand_rph in post #4
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. It is a small point and it changes the answer, which is an awkward combination.

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CT
cannula_traceTL3Regular1 Apr 2026#1

A checklist for reading a certificate in under two minutes — setting out what I have, and where I think it stops being reliable.

I would like to understand what this number means before I repeat it anywhere.

A PeptideMeter report on a semaglutide lot gives 96.8% purity. The supplier certificate for the same lot states 98.1%. Both documents name a reversed-phase method; neither states the same gradient.

My question is not "who is right". It is: given that those two figures were produced by different methods, what is the largest difference I should expect from method alone, and at what point does a gap stop being explainable that way?

60 likes 4mo
PE
ppm_errorTL3Analytical chemist5 Apr 2026#2

"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.

It is worth stating the boring hypothesis before the interesting one.

17 likes 4mo
HB
h.bakkerTL28 Apr 2026#3

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".

Somebody will have a better source than mine, and I hope they post it.

6 likes 4mo
MS
m.strand_rphTL3Pharmacist Solution11 Apr 2026#4
ppm_error, post #2: "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. It is worth stating the boring hypothesis before the interesting one. Go to post

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.

It is a small point and it changes the answer, which is an awkward combination.

8 likes in reply to #2 4mo
RL
r.lundgrenTL213 Apr 2026#5
ppm_error, post #2: "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. It is worth stating the boring hypothesis before the interesting one. Go to post

Everything in post #3 holds. The case it does not cover is the one I have.

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.

24 likes in reply to #2 3mo
QZ
q.zhao_qaTL3Quality assurance16 Apr 2026#6

Narrowing post #3, because the general version has more than one 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.

11 likes 3mo
SA
s.antonsenTL218 Apr 2026#7

Following, with nothing to contribute beyond having asked the same thing elsewhere.

3 likes 3mo
FP
forest_plotTL3Evidence synthesis20 Apr 2026#8
m.strand_rph, post #4: 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. It is a small point and it changes the answer, which is an awkward combination. Go to post

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.

Adding a source would improve this post and I do not have one to hand.

0 likes in reply to #4 3mo
BD
b.dumitruTL222 Apr 2026#9
m.strand_rph, post #4: 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. It is a small point and it changes the answer, which is an awkward combination. 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".

It reads as pedantry until the day it does not.

17 likes in reply to #4 3mo
EN
electrolyte_notesTL2Regular24 Apr 2026 · edited#10

The arithmetic in post #8 is right; the assumption feeding it is the part to check.

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.

7 likes 3mo
IA
i.amankwahTL226 Apr 2026#11

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".

10 likes 3mo
TN
t.nardoneTL3Regular28 Apr 2026#12

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.

22 likes 3mo
AL
a.lindqvistTL230 Apr 2026#13
r.lundgren, post #5: Everything in post #3 holds. The case it does not cover is the one I have. 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. Go to post

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.

That distinction has done more work for me than anything else in this category.

0 likes in reply to #5 3mo
JV
j.vandermolenTL3Regular2 May 2026#14

Good question, well framed, and I would like to see it answered properly.

1 like 3mo
SD
st.dialloTL24 May 2026#15

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.

6 likes 3mo
GV
g.valckenaereTL3Regular6 May 2026#16

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

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

16 likes 3mo
ST
s.teixeiraTL28 May 2026 · edited#17
forest_plot, post #8: 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. Adding a source would improve this post and I do not have one to hand. Go to post

Confirming post #16 from a second method, which matters more than confirming it from a second person.

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.

The strength of my opinion here exceeds the strength of my evidence.

31 likes in reply to #8 3mo
H
HHidalgoTL2Member10 May 2026#18

I had written a reply contradicting post #15 and deleted it. Here is what survived.

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.

The number is defensible. The precision I gave it is not.

0 likes 3mo
TV
t.verhoevenTL211 May 2026#19

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.

Flagging that the sources on this are thinner than the confidence in the thread suggests.

21 likes 3mo
TT
taper_tableTL3Regular13 May 2026#20
g.valckenaere, post #16: Asking for the batch record rather than the certificate is a reasonable request and the response to it is informative whichever way it goes. If that is already documented somewhere, ignore me and link it. Go to post

On post #18 — agreed on the reasoning, with one qualification.

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".

Genuinely open to being wrong about this one.

0 likes in reply to #16 3mo
DF
d.ferreiraTL215 May 2026#21
ppm_error, post #2: "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. It is worth stating the boring hypothesis before the interesting one. Go to post

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.

16 likes in reply to #2 2mo
BV
bias_varianceTL4Biostatistician16 May 2026#22

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.

That has been true for the cases I have seen and I have not seen many.

6 likes 2mo
SO
s.ostergaardTL218 May 2026#23

I had written a reply contradicting post #19 and deleted it. Here is what survived.

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.

One of those cases where knowing the mechanism does not help the decision.

0 likes 2mo
IT
impurity_tableTL3Analytical chemist20 May 2026#24

Understood, and I withdraw the assumption I opened with.

32 likes 2mo
IB
i.balogunTL221 May 2026#25
r.lundgren, post #5: Everything in post #3 holds. The case it does not cover is the one I have. 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. 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".

On reflection I would soften that slightly.

23 likes in reply to #5 2mo
TY
two_year_lineTL3Regular23 May 2026#26
impurity_table, post #24: Understood, and I withdraw the assumption I opened with. Go to post

Picking up post #23: that is the part I would want checked first.

Where two documents for the same lot disagree, the useful question is which was measured and which was transcribed. Most such disagreements are the second.

If that reads as pedantic, it is, and it has saved me twice.

10 likes in reply to #24 2mo
CC
c.chowdhuryTL225 May 2026#27

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.

1 like 2mo
B
batchlogTL3Regular26 May 2026 · edited#28

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 2mo
JS
j.sandvikTL228 May 2026#29

Everything in post #27 holds. The case it does not cover is the one I have.

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.

The interesting part of this is the exception, and I do not understand the exception.

7 likes 2mo
AT
a.thorneTL2Wiki editor30 May 2026#30

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.

1 like 2mo
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