What a Certificate of Analysis is — and what it is not
A Certificate of Analysis (COA) is a document issued by a testing laboratory that records the analytical results for a specific batch of a material. When it is issued by an independent, accredited laboratory, it represents an objective, third-party determination of what a particular lot contains and whether it meets defined specifications.
A COA is not a product endorsement. It does not mean a compound is safe, legal, or suitable for any particular use. It is a statement of analytical fact about a defined sample at the time of testing. The distinction matters: the COA tells you what is in the vial; it says nothing about whether it is appropriate for you to use it.
In the UK research peptide market, where no regulatory body has audited the supply chain or licensed the product, the independent COA is the primary instrument of quality verification. But only if you can read it properly — and only if the document you are given is a genuine COA rather than a marketing document dressed up to resemble one.
The independence question first: Before reading any field in detail, ask who issued the document. A COA signed by the selling supplier's own quality team, or bearing the supplier's logo without reference to an external laboratory, carries far less evidential weight than one issued by an accredited analytical facility with no commercial relationship to the seller. Establish independence before you evaluate content.
The fields that matter, one by one
Lot number / batch reference
The lot number is the most important single identifier on a COA. It links the analytical results to one specific production batch and no other. When you receive a vial, the lot number printed on the label should match the lot number on the COA exactly. If the COA refers to a general product line, a product code, or a date range rather than a specific batch reference, it is not a batch-level COA — it is a product-level claim, which tells you nothing about the particular vial in front of you.
UK buyers should also note that the lot number is your reference if you ever need to raise a quality concern, request supporting documentation, or trace the batch back through the supply chain. A COA without a unique, specific lot number has no traceability value.
HPLC purity — the main analytical claim
High-Performance Liquid Chromatography (HPLC) is the standard method for determining purity in peptide analysis. The technique separates the components of a sample by passing them through a chromatography column under high pressure, then detects them — most commonly by ultraviolet absorbance at 220 nm, which responds to the peptide bond. The result is a chromatogram: a graph of detector response against time, with peaks corresponding to the individual components present.
The purity figure reported — say, 98.4% — is the area of the main peak expressed as a proportion of the total peak area detected. This means that 98.4% of what the detector saw was the target compound. The remaining 1.6% is distributed among minor peaks: residual reagents, deletion sequences (fragments missing one or more amino acids), oxidation products, or other impurities.
For UK research applications, the commonly cited minimum threshold is 98% purity by HPLC. Some applications demand higher — 99% or better — particularly where the research design is sensitive to trace impurities. The relevant question is whether the specification matches the research context, not whether a number above 98% is inherently sufficient.
The chromatogram itself, not just the percentage, is what transforms a claim into evidence. A single dominant peak with a clearly resolved baseline, no significant co-eluting impurities, and a visible integration table is what a genuine HPLC result looks like. A percentage stated without the supporting trace is a headline without the article behind it.
LC-MS identity confirmation
Liquid Chromatography–Mass Spectrometry (LC-MS) combines the separation power of HPLC with mass spectrometric detection to confirm the identity of the target compound. Where HPLC measures the relative amount of a peak, LC-MS determines whether the compound producing that peak is actually the molecule claimed on the label.
The principle is straightforward: every molecule has a characteristic mass-to-charge ratio (m/z). A mass spectrometer ionises the sample and sorts the resulting ions by their m/z values, generating a spectrum. If the observed molecular mass matches the calculated theoretical mass of the claimed peptide — within the instrument's tolerance, typically within a few daltons for standard electrospray ionisation — identity is confirmed.
This matters because HPLC purity alone does not establish what the dominant peak actually is. A batch could show 99% purity by HPLC and still be 99% of the wrong peptide. LC-MS is the check that closes this gap. A COA reporting high HPLC purity but no mass spectrometry identity check is analytically incomplete.
Look for the observed m/z or molecular mass alongside the theoretical value and a stated tolerance. Some COAs report multiple charge states (e.g. [M+2H]²⁺, [M+3H]³⁺) for larger peptides, which is appropriate and demonstrates rigorous method execution.
Karl Fischer water content
Peptides are hygroscopic — they absorb water from the atmosphere. The water content of a batch affects its true potency: a sample reported as 10 mg may contain significantly less than 10 mg of active peptide if a substantial fraction of that mass is water. Karl Fischer titration is the standard analytical method for measuring water content in pharmaceutical and research materials, referenced in the ISO 760 family of standards and in the European Pharmacopoeia.
Typical water content for a lyophilised (freeze-dried) research peptide runs between roughly 5% and 15%, though this varies by compound and storage history. A value significantly above this range may indicate poor storage, inadequate lyophilisation, or rehydration during shipping. A water content reported as zero or unrealistically low may indicate the test was not properly conducted or the value was fabricated.
The Karl Fischer result also allows a buyer to calculate the net peptide content more accurately. If a vial nominally contains 10 mg and water content is reported at 8%, the actual peptide content is closer to 9.2 mg. For quantitative research designs, this correction is not trivial.
Endotoxin / pyrogen testing
Endotoxins are lipopolysaccharide components of the outer membrane of Gram-negative bacteria. They are heat-stable, meaning they survive sterilisation processes that would kill the bacteria themselves, and they are potent pyrogens — substances that induce fever and inflammatory responses. For any research application that involves contact with biological systems, the endotoxin content of a research material is a meaningful quality parameter.
The standard method for endotoxin testing is the Limulus Amebocyte Lysate (LAL) assay, which exploits the coagulation response of horseshoe crab blood cells to endotoxins. Results are expressed in Endotoxin Units per milligram (EU/mg). The pharmacopoeial limit for injectable materials is 5 EU/kg body weight per hour, but for research peptides, suppliers typically aim to deliver material below 1 EU/mg or — in higher-specification preparations — below 0.1 EU/mg.
Not all research peptide COAs include endotoxin data. Its presence indicates that the supplier has gone beyond the minimum HPLC and MS checks and is supplying material to a more comprehensive quality standard. For research applications where sterility and biological compatibility matter, this field should be considered essential rather than optional.
Appearance and physical description
Most research peptides are supplied as white to off-white lyophilised powders, though some compounds appear as slightly yellowish or beige solids depending on their composition. The appearance field on a COA records the physical state and colour of the batch as observed at time of testing. It is a simple visual check, but it serves two purposes: it provides a baseline for comparison when you receive the vial, and it flags any significant deviation from the expected physical form that might indicate degradation, contamination, or incorrect material.
If your vial contains material that is visibly darker, has a different texture, or shows signs of clumping that are unusual for the compound, comparing to the appearance recorded on the COA is a reasonable first step. A significant discrepancy is a reason to query the batch before use.
Test date, method reference, and signatory
A COA issued in 2022 for a batch you are purchasing in 2026 is not a current quality certificate — it is a historical record. Peptides can degrade over time, particularly if stored improperly. The test date should be recent relative to the batch's production and dispatch. Many suppliers re-test before dispatch or have COAs generated close to the time of fulfilment. A very old test date, or an undated document, should prompt clarification.
The method reference is the analytical procedure used for each test — for example, referencing a specific HPLC method (column, mobile phase, gradient, detection wavelength) or citing the Karl Fischer titration standard. Method references demonstrate that the analysis was conducted to a defined and reproducible protocol, not ad hoc. Their absence makes the result harder to evaluate and impossible to reproduce or challenge.
The signatory is the person at the issuing laboratory who takes responsibility for the results. A named scientist with a stated role, rather than a generic stamp or no signature at all, turns the document into an auditable record with accountable authorship. For a COA issued by a properly accredited laboratory, you should expect to find a named analyst or quality manager, the laboratory's accreditation details, and a date of issue.
Red flags on a COA: what should concern you
The following are patterns that experienced buyers and analytical chemists have identified as indicators of a document that deserves scepticism:
- No lot number, or a lot number that does not match your vial. If the numbers do not correspond, the COA does not certify what you have received.
- A COA issued by the seller, not an independent laboratory. Self-certification is not verification. The entire value of the COA rests on the independence of the issuing party.
- HPLC percentage only, with no chromatogram. A number without the supporting data is an assertion, not evidence.
- No LC-MS identity confirmation. High purity of the wrong compound is not quality.
- Water content reported as zero. Peptides absorb water. A zero result is almost certainly incorrect or indicates the test was not performed.
- A single COA covering multiple products or a product range. Batch-level analysis applies to one batch. A single document certifying a product line is not a COA — it is a specification sheet.
- No accreditation details for the laboratory. A credible analytical laboratory will reference its accreditation — in the UK context, look for UKAS accreditation (ISO/IEC 17025) or an equivalent international standard.
Why UK buyers should apply these standards consistently
In the United Kingdom, research peptides sit outside the MHRA's licensed medicine framework. There is no compulsory batch-release testing, no mandated COA format, and no regulatory body auditing the analysis that goes into the document you receive. The standards described in this guide are not legal requirements for research compounds — they are the standards a diligent buyer should demand precisely because no one else is requiring them on their behalf.
Reading a COA critically is not a specialist skill. It is the basic due diligence that the absence of regulation makes necessary. The analytical methods involved — HPLC, LC-MS, Karl Fischer, LAL — are well-established, widely understood, and the reports they generate follow recognisable formats. Once you know what to look for, distinguishing a genuine analytical record from a marketing document becomes considerably more straightforward.
Putting it together: a working checklist
When you receive a COA from a supplier, work through the following in order:
- Confirm the lot number on the document matches the lot number on your vial.
- Check who issued the document — is it an independent, named laboratory, or the supplier itself?
- Look for the HPLC purity percentage and the supporting chromatogram. Is the purity at least 98%? Is the chromatogram included?
- Check for LC-MS identity confirmation. Is the observed mass stated alongside the theoretical mass?
- Look for Karl Fischer water content. Is a value given, and is it within a plausible range?
- Check for endotoxin data if biological compatibility is relevant to your application.
- Note the test date and the signatory. Is the test recent? Is there a named analyst?
- Look for the laboratory's accreditation details — ideally a UKAS number or ISO/IEC 17025 reference.
A COA that passes all eight checks is a document that carries genuine evidential weight. One that fails on multiple points — particularly the first two — should prompt you to request a better document or reconsider the supplier.