# How to Read a Peptide Certificate of Analysis

A certificate of analysis is the document that says what is in the vial and how it was tested. This guide explains what the purity percentage measures, why purity alone does not prove you have the right compound, what each of the two standard tests proves, how to read a certificate field by field, and the warning signs worth knowing.

- Source: https://www.australianresearchpeptides.au/articles/peptide-testing-purity-coa
- Reading time: 6 minute read
- Published: 2026-08-10
- Updated: 2026-09-02
- Publisher: Australian Research Peptides

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## What Does the Purity Percentage Mean?

It is the share of the sample that is the compound you ordered. A batch reported at 99% means the target compound made up 99% of what the instrument detected.

The number exists because peptides are built one piece at a time. Each step is a chance for something to go slightly wrong — a piece that fails to attach, or a side reaction that makes a near-copy. So the raw product of any synthesis is never one clean substance. It is the peptide you wanted plus a crowd of close relatives, and purification is the work of removing as many relatives as possible.

The purity figure describes what survived that clean-up.

## Why Purity Alone Is Not Enough

Here is the thing almost nobody is told: **a high purity figure does not prove you have the right compound.**

Purity measures whether the sample is _one thing_. It does not measure whether that one thing is the _right_ thing.

Picture a synthesis that consistently misses a single amino acid. The result is a peptide one piece short. If that peptide cleans up nicely, the purity test reports an excellent result — because the sample really is almost entirely one substance. It is just the wrong substance.

Only weighing the molecule catches that. Which is why a certificate needs two tests, not one.

## Why Two Tests Instead of One?

A certificate carries two tests because they answer different questions.

_The two standard tests on a peptide certificate and the question each one answers_

| Test | The question it answers |
| --- | --- |
| HPLC | How much of this sample is one substance? |
| Mass spectrometry | Is that substance the one on the label? |

**HPLC** pushes the dissolved sample through a packed tube. Different molecules travel through at different speeds, so they come out separated. A detector counts what comes out and when, and the result is a graph of peaks. Comparing the size of the target peak against all the peaks gives the purity percentage.

**Mass spectrometry** weighs the molecule. Because a peptide’s exact weight can be calculated in advance from its recipe, the test is simple: does the measured weight match the calculated one? A good certificate prints both figures side by side so you can check.

Reading a purity graph in ten seconds.

One tall sharp peak with a flat line either side, plus a few small ones, is what a well-purified peptide looks like. A broad peak, a bump on the side of the main peak, or several peaks of similar height means a mixture.

_Figure: Reading a chromatogram and a mass spectrum — What the two traces look like side by side, and which question each one answers about the same batch._

## Which Question Does Each Test Answer?

Every line on a certificate answers one question and leaves others open. Reading a document well is mostly a matter of not letting a result travel further than the method behind it.

_Each kind of evidence on a certificate, what it can support, and what it does not establish on its own_

| Evidence on the document | What it can support | What it does not establish by itself |
| --- | --- | --- |
| HPLC chromatogram and area result | The separation profile under the stated method, and the relative detected peak area | Molecular identity, total vial mass, sterility or endotoxin state |
| Mass spectrum or LC–MS result | An observed mass consistent with the expected molecule | Chromatographic purity, the exact quantity in the vial, sterility or endotoxin state |
| Assay or content result | The amount present under the specified assay, where an actual assay is reported | Identity, unless the method also supports it |
| Batch or lot identifier | A traceability key, when the same identifier appears on the record being offered | That a differently labelled vial came from that batch |
| Laboratory, method and test date | Who reported what, by which method, and when | Independence, accreditation or authenticity, unless separately verified |

## What the Tests Cannot Tell You

Three limits are worth knowing, because none of them is obvious.

- **The percentage is not a weight.** The detector mostly sees peptide-like material. Salt and water barely register. So a vial can be 99% pure by the test and still be a fair amount of salt and moisture by weight. That is normal for freeze-dried peptides and is not a sign of a problem — it is simply a different measurement.
- **Anything invisible to the detector is not counted.** The figure compares the peaks that appeared. Something that does not show up at all cannot be in the sum.
- **Neither test says anything about biology.** A batch can be analytically excellent and still behave unexpectedly in an experiment. And neither test says anything about safety or suitability for use in humans or animals.

## What Is a Certificate of Analysis?

It is the document that records what a batch is and how it tested: this compound, this batch, this method, this date, this result.

Most people meet their first one as a PDF and skim it for the purity number, which on its own is the least useful thing on the page. Break any link in that chain — the compound, the method, the date — and the number stops meaning much.

The one check worth doing every time.

Find the stock code for your material — it is on the product page and on your order — then open the certificate filed under it in the

[CoA library](https://www.australianresearchpeptides.au/coa)

. Check that the compound and the strength on the certificate are the ones you are buying. If you need the certificate for one particular parcel,

[ask us](https://www.australianresearchpeptides.au/contact)

with the order reference.

_Figure: A Certificate of Analysis, read field by field — A screen walkthrough of a real certificate — identity block, method, result and dates, in the order they appear._

## How Do You Read a Certificate?

Four things are worth finding, in this order.

### The Compound Named at the Top

Check it against your order and the product page. It costs nothing and catches the errors that matter most. A blend should name both of its components. If the certificate uses a name you do not recognise, that is usually just a synonym rather than a problem — peptides collect alternative names freely.

### The Result, With Its Method

A result should say how it was measured. “98.4% by HPLC” is more informative than “over 99% pure” with no method and no date, even though the second one reads better.

**Treat round numbers with mild suspicion.** Real measurements come out untidy. A supplier reporting exactly 99.0% across an entire catalogue is quoting a target, not a set of measurements.

The figure ARP publishes on product pages is a minimum a batch must clear, not a reading from any particular vial. The measured number for your batch is on the certificate, which is why the certificate is the document that counts.

### The Dates

Two are worth finding: when the material was made, and when it was tested. The gap between them tells you whether it was tested fresh. A large gap is not automatically a problem, but it is context.

Some certificates carry a retest or expiry date. That is a statement about how long the supplier stands behind the result, not a prediction that the compound falls apart the next morning. In practice, [how the powder is stored](https://www.australianresearchpeptides.au/articles/lyophilised-peptides-storage-handling) matters more than the printed date.

### Who Issued It

A certificate should name the laboratory and carry a signature and contact details. That is what makes it traceable, so somebody can be asked about it. An anonymous certificate cannot be followed up, which limits how much it is worth.

Testing by an independent laboratory carries more weight than in-house testing, for the obvious reason that the party doing the measuring has no stake in the answer.

## How Do You Match a Certificate to a Product?

A shared compound name is the weakest possible link between a document and a vial. The connection worth trusting runs through a batch or lot identifier that appears on both.

1. Start on the exact product and strength record, not a parent page.
2. Note the product identity, the nominal strength, the stock code and any displayed batch or lot reference.
3. Follow the certificate link published for that record. Do not pick a document because its compound name looks similar.
4. Check that the document’s sample identity and batch reference agree with the record you started from.
5. Read the method and the result together. A percentage with no method and no traceable sample context is incomplete evidence.
6. Check the laboratory identity and the test date, then follow whatever verification route the laboratory itself provides.
7. Write down what the document does **not** test. An HPLC and mass-spectrometry report is not a sterility result, an endotoxin result, or a statement of total vial content.

### A Current Example, Field by Field

The record below is chosen from this site’s published certificates at build time, so it is a current one rather than an illustration. Each row says what that field genuinely means — and the last two rows are the ones most often over-read.

_A currently published certificate, field by field, with what each field does and does not mean_

| Field | What it means | On this record |
| --- | --- | --- |
| Supplier record | The exact listing the document is published against — not the compound in general | [Retatrutide 10 mg](https://www.australianresearchpeptides.au/products/retatrutide/10mg) |
| Stock code | The identifier that ties the listing, the order line and the vial together | ARP-RET-10 |
| Sample identity | The name and nominal amount the laboratory was asked to analyse | Retatrutide, 10 mg nominal |
| Batch or lot | The traceability key. Without one shared by both the listing and the document, the two are connected only by a compound name | Printed on the document. This site publishes no separate batch register, so read it from the certificate itself |
| Laboratory and test date | Who reported the result and when. Neither is evidence of independence or accreditation on its own | Both printed at the head of the document |
| Method | A purity figure means nothing without the method that produced it | Chromatographic purity with mass confirmation, as stated on the report |
| Purity result | Detected peak area under the stated method — a separation result, not a statement of identity or of vial mass | 99.861% |
| Not tested | The most useful line on any certificate is the list of questions it did not ask | Sterility, endotoxin content and total vial mass are not established by this report |

[Open the certificate for Retatrutide 10 mg](https://www.australianresearchpeptides.au/assets/coa/retatrutide-10-coa.png?v=111) and check each row against the document, or browse every published record in the [certificate library](https://www.australianresearchpeptides.au/coa).

A disclosure.

Australian Research Peptides sells products discussed in this guide. The example above is a first-party catalogue record linked to its own laboratory document; it is not an independent review of this business. Every figure in it can be checked against the original certificate, and the

[editorial policy](https://www.australianresearchpeptides.au/editorial-policy)

sets out how these guides are written.

## What Are the Warning Signs?

- A purity figure with no method stated.
- Purity reported but identity never confirmed.
- No dates anywhere on the document.
- Identical figures across an entire catalogue.
- No laboratory named, and no signature.
- A certificate that cannot be matched to the batch you actually received.

## What ARP Publishes

The [CoA library](https://www.australianresearchpeptides.au/coa) lists every peptide product and strength Australian Research Peptides supplies, with the laboratory’s own certificate attached wherever one has been issued. It is worth opening in a second tab while reading this page, because every section above describes something you can go and look at.

If you need the certificate covering one specific consignment rather than the published one, [ask us](https://www.australianresearchpeptides.au/contact) with your order reference.

In vitro research purposes only.

This article describes laboratory testing and the documents that report it. Certificates of Analysis describe chemical identity and purity. They are not quality, safety or suitability statements for any use in humans or animals, and nothing here is medical, therapeutic or dosing guidance. All products supplied by Australian Research Peptides are for in vitro research purposes only.

Australian Research Peptides publishes the laboratory's own report rather than retyping a figure out of it — 12 of them are on the [certificates page](https://www.australianresearchpeptides.au/coa), one per product and strength, against material tested batch by batch and held in Sydney.

## References

1. [ICH Q6A. Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical Substances. Step 4, 6 October 1999](https://database.ich.org/sites/default/files/Q6A%20Guideline.pdf)
2. [Wu LC, Chen F, Lee SL, et al. Building parity between brand and generic peptide products: regulatory and scientific considerations for quality of synthetic peptides. Int J Pharm 2017;518(1-2):320-34 (PMID 28027918)](https://pubmed.ncbi.nlm.nih.gov/28027918/)
3. [Lian Z, Wang N, Tian Y, et al. Characterization of synthetic peptide therapeutics using liquid chromatography-mass spectrometry: challenges, solutions, pitfalls, and future perspectives. J Am Soc Mass Spectrom 2021;32(8):1852-60 (PMID 34110145)](https://pubmed.ncbi.nlm.nih.gov/34110145/)
4. [Qian Cutrone JJ, Huang XS, Kozlowski ES, et al. Tiered analytics for purity assessment of macrocyclic peptides in drug discovery: analytical consideration and method development. J Pharm Biomed Anal 2017;138:166-74 (PMID 28213177)](https://pubmed.ncbi.nlm.nih.gov/28213177/)
5. [Chatterjee S, Bandyopadhyay A. Synthesis and characterization of two potential impurities (des-ethyl-Ganirelix) generated in the Ganirelix manufacturing process. J Pept Sci 2023;29(9):e3489 (PMID 36967632)](https://pubmed.ncbi.nlm.nih.gov/36967632/)

## Related guides

- [Storing Freeze-Dried Peptides: A Plain Guide](https://www.australianresearchpeptides.au/articles/lyophilised-peptides-storage-handling)
- [Peptide Types, Categories and Blends](https://www.australianresearchpeptides.au/articles/peptide-types-categories-blends)

## Related compounds

- [Retatrutide](https://www.australianresearchpeptides.au/products/retatrutide)
- [GHK-Cu](https://www.australianresearchpeptides.au/products/ghk-cu)
- [BPC-157](https://www.australianresearchpeptides.au/products/bpc-157)

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_All products supplied by Australian Research Peptides are for in vitro research purposes only._