What is a certificate of analysis (COA)?
A certificate of analysis (COA) is a document produced by an analytical laboratory that records the results of the tests run on a specific batch of a material. For a research peptide, it answers two core questions: is this the compound it claims to be (identity), and how much of the sample is that compound (purity). A COA turns an otherwise anonymous vial of white powder into a traceable, documented material.
The most important word in that definition is batch-specific. Each production run — each lot — is tested on its own, and its COA reports the numbers for that lot alone. A meaningful certificate carries a lot or batch number that matches the label on the vial in hand, so the material can always be tied back to the exact data generated from it. A certificate with no lot number, or one reused across every order, documents very little.
The essentials at a glance
Batch-specific proof
Each lot has its own certificate, tied to the lot number on the vial — not a generic, reused document.
HPLC purity
Reversed-phase HPLC separates the sample and reports the target peptide as a percentage of the whole.
Mass-spec identity
Mass spectrometry confirms the molecule is the intended sequence by matching its measured mass to the theoretical mass.
Research use only
A COA documents analytical quality — it makes no claim about efficacy or use in humans or animals.
Every compound ships with its COA
Browse Peptora's catalog of research compounds — each HPLC-verified to 99%+ purity with a batch-specific certificate of analysis, for laboratory research use only.
Shop HPLC-tested compoundsHow HPLC purity testing works
HPLC — high-performance liquid chromatography — is the workhorse method for measuring peptide purity, and the source of the headline purity figure on most COAs. The principle is separation: the dissolved sample is pushed under high pressure through a column packed with a fine stationary material, and different molecules travel through it at different speeds depending on their chemistry.
For peptides the standard approach is reversed-phase HPLC (RP-HPLC), which separates molecules by how strongly they interact with a non-polar surface. As each component leaves the column it passes a detector — most commonly a UV detector — producing a chromatogram: a plot of signal versus time, with each distinct compound appearing as its own peak.
- The main peak represents the target peptide. Its share of the total detected signal — the area percent — is reported as the purity figure (for example, 99.2%).
- Smaller peaks are impurities: closely related sequences, truncated or deleted fragments, or process residues that separated out from the main compound.
- Method conditions matter — the column, solvent gradient, and wavelength are chosen so that impurities actually resolve away from the main peak rather than hiding beneath it.
- Orthogonal checks are used because a single peak can occasionally mask a co-eluting impurity; analysts may pair HPLC with mass spectrometry or a second, differently-selective separation to confirm a peak is truly pure.
Confirming identity with mass spectrometry
HPLC tells you how pure a sample is; it does not, on its own, prove the main peak is the right molecule. That is the job of mass spectrometry (MS). An MS instrument ionizes the sample and measures the mass-to-charge ratio of the resulting ions, letting analysts determine the compound's molecular mass with high precision.
Because a peptide's exact mass is fixed by its amino-acid sequence, the measured mass can be compared directly against the theoretical mass calculated from the intended sequence. When the two agree within the instrument's tolerance, identity is confirmed. Coupling the two techniques — LC-MS, in which the HPLC separation feeds directly into the mass spectrometer — lets a laboratory verify identity and assess purity in a single, linked analysis.
- Identity confirmation — the measured molecular mass matches the mass expected from the target sequence.
- Impurity characterization — the masses of minor peaks can reveal *what* an impurity is (for example, a sequence missing one residue), not just that it exists.
- Orthogonality — MS answers a different question than HPLC (identity vs. relative amount), so the two together give a more complete picture than either alone.
What "99%+ purity" actually means
When a COA reports "99%+ purity," it means that, by the HPLC method used, at least 99% of the detected material is the target compound and less than 1% is made up of impurities. It is a statement about the composition of the powder — a measure of material quality — and nothing more.
Two clarifications keep the figure honest. First, purity is method-dependent: a purity number is only as meaningful as the HPLC method behind it, which is why a COA lists the method conditions alongside the result. Second, purity is not the same as net peptide content — the fraction of the total powder weight that is actually peptide, as opposed to bound water, salts, and counter-ions. A batch can be 99%+ *pure* (little else that is peptide-like) while a separate figure accounts for the non-peptide mass. Good COAs may report both.
This is why documentation is treated as standard rather than optional across the catalog: every compound — from GLP-3 RT to BPC-157 and TB-500 — is characterized the same way and ships with its own batch-specific certificate.
How to read a certificate of analysis
Most COAs share a common anatomy. Once you know what each field reports, a certificate takes only a moment to read — and the fields that are *missing* are often as telling as the ones that are present.
| COA field | What it reports | Why it matters |
|---|---|---|
| Product / peptide name | The identity of the compound tested | Confirms the certificate matches what was ordered |
| Batch / lot number | A unique code for the specific production run | Ties the exact vial in hand to its own test data |
| HPLC purity (%) | The share of the sample that is the target peptide | The headline material-quality figure — e.g. 99%+ |
| Identity (MS) | Measured molecular mass vs. the theoretical mass | Confirms the peptide is the intended sequence |
| Net peptide content | Peptide mass excluding water, salts, and counter-ions | Separates total powder weight from actual peptide mass |
| Appearance / physical form | e.g. white lyophilized powder | A first-pass visual quality check |
| Test date / analyst | When, and by whom, the analysis was run | Establishes the documentation is current and traceable |
Standards bodies formalize this discipline. Bodies such as the United States Pharmacopeia (USP) publish reference standards and analytical procedures, and the International Council for Harmonisation (ICH) guidelines — including Q6 on specifications and Q7 on quality practices — describe how identity, purity, and impurity limits are established and documented. A research supplier's COA borrows the same analytical logic: define the method, report the result, and tie it to a specific lot.
Scientific references
The literature below, indexed in PubMed, describes the analytical techniques behind a peptide certificate of analysis — HPLC purity determination, mass-spectrometric identity confirmation, impurity analysis, and reference standards for quality:
- 1Lian Z, 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):1852-1860. doi:10.1021/jasms.0c00479 (PMID: 34110145).
- 2Karongo R, et al. A selective comprehensive reversed-phase × reversed-phase 2D-liquid chromatography approach with multiple complementary detectors as an advanced generic method for the quality control of synthetic and therapeutic peptides. J Chromatogr A. 2020;1627:461430. doi:10.1016/j.chroma.2020.461430 (PMID: 32823119).
- 3Stoll DR, et al. A strategy for assessing peak purity of pharmaceutical peptides in reversed-phase chromatography methods using two-dimensional liquid chromatography coupled to mass spectrometry. J Chromatogr A. 2023;1693:463873. doi:10.1016/j.chroma.2023.463873 (PMID: 36871316).
- 4Prabhala BK, et al. Characterization of Synthetic Peptides by Mass Spectrometry. Methods Mol Biol. 2015;1348:77-82. doi:10.1007/978-1-4939-2999-3_9 (PMID: 26424265).
- 5McCarthy D, et al. Reference Standards to Support Quality of Synthetic Peptide Therapeutics. Pharm Res. 2023;40(6):1317-1328. doi:10.1007/s11095-023-03493-1 (PMID: 36949371).
- 6Hetrick EM, et al. Mass balance analysis for therapeutic peptides: case studies, applications, and perspectives. J Pharm Biomed Anal. 2024;252:116501. doi:10.1016/j.jpba.2024.116501 (PMID: 39442464).
Compare COAs across the catalog
Every Peptora research compound is HPLC-verified to 99%+ purity and ships with a batch-specific certificate of analysis — for laboratory research use only.
Browse research compoundsKey takeaways
- A certificate of analysis (COA) is a batch-specific laboratory document that reports the identity and purity of a specific production lot of a compound.
- HPLC (high-performance liquid chromatography) is the standard method for quantifying purity — it separates a sample into peaks and reports the target peptide as a percentage of the total detected signal.
- Mass spectrometry confirms identity by measuring the compound's molecular mass and matching it to the theoretical mass of the intended sequence; LC-MS pairs the two techniques.
- "99%+ purity" is a material-quality measure — at least 99% of the sample is the target compound — and says nothing about biological activity, potency, or suitability for any use in humans or animals.
- A trustworthy COA is batch-specific (tied to the lot number on the vial), dated, and lists the analytical method — a generic, lot-less, or undated certificate is a red flag.
- Every Peptora research compound is HPLC-verified to 99%+ purity and ships with a batch-specific COA, for laboratory research use only.
Frequently asked questions
This article is intended solely as an educational summary of publicly available scientific literature. Products offered by Peptora are supplied exclusively for laboratory research purposes and are not approved for human or veterinary use. The information presented should not be interpreted as medical advice, treatment recommendations, or clinical guidance.
