How to Read a Peptide Certificate of Analysis (COA)

What a certificate of analysis is

A certificate of analysis (COA) is a laboratory's report on one submitted sample of one lot. It names the material, the lot or batch identifier, the tests that were run, the specification each result was compared against, the result, and whether the result met the specification. It is signed or verifiable by the laboratory that did the work, and it applies only to the sample that was tested; every certificate in our library says so in its own terms.

Three things a COA is not: it is not a general description of a product, it is not a guarantee about vials that were never sampled, and it is not an assessment of anything that was not tested. Reading those caveats is part of reading the certificate.

Why researchers review COAs

A research-use-only peptide is sold as a reference material for laboratory work. Its value depends on three independent facts: that the vial contains the compound named on the label (identity), that most of the peptide material is that compound rather than related impurities (purity), and that the vial contains the quantity the label states (content). Regulatory guidance lists identity, purity and quantity (assay) as separate attributes, each needing its own test ^[4][3], and a COA is where a laboratory reports each one.

Reviewing the certificate before an experiment lets a researcher record the lot, the measured purity and the measured content in the lab notebook, use the measured content for concentration calculations, and compare lots over time.

What HPLC testing measures

High-performance liquid chromatography (HPLC) pumps a dissolved sample through a column packed with fine particles. Components separate because they interact with the column packing to different degrees; for peptides the usual mode is reversed-phase chromatography on a C18 column, where more hydrophobic molecules are retained longer. A detector at the column outlet records a signal over time. The plot of that signal is the chromatogram, and each separated component appears as a peak ^[1].

Two numbers describe a peak: its retention time, the minutes between the sample entering the column and the peak maximum, and its area, the integrated signal under the peak. On our certificates the detector is ultraviolet absorbance, usually at 214 nm or with a diode-array detector (DAD) that records a full spectrum ^[1].

Understanding HPLC purity percentages

Chromatographic purity is the main peak's area expressed as a percentage of the summed area of every integrated peak. A result of 99.99 % means that 99.99 % of the integrated signal came from the main peak. Three limits of the number follow directly from how it is calculated:

• It counts only what the detector can see. A substance that does not absorb at the detection wavelength, or that elutes outside the analysed window, is not in the denominator.
• It is a percentage of detected peptide-related material, not a percentage of the powder's mass. Water, counter-ions such as trifluoroacetate or acetate, and residual solvent do not appear as peaks, so a 99.99 % purity vial can still hold less peptide by mass than its label states. The KMD certificates say this directly: chromatographic purity "is not a measure of net peptide mass content (what fraction of the powder is peptide versus counter-ion, water, or residual solvent)".
• Closely related impurities can co-elute with the main peak. Deletion sequences, diastereomers and oxidised forms are the common synthesis-related impurities in peptides ^[5], and a single HPLC method does not separate every one of them. That is why regulators set thresholds above which peptide-related impurities must be reported, identified and qualified, expect additional independent methods when one method cannot separate them, and rely on mass spectrometry to establish their structures ^[3][6].

The Thymosin Alpha-1 10 mg certificate above (KMD Analytical, certificate PPL-20261102-X2NF-01, analysed November 2, 2026) is a clear example. The laboratory reports chromatographic purity of 99.99 % of total peak area with the main peak at 6.899 minutes, and separately reports content per vial of 9.22 mg against a 10 mg label claim, which is 92.2 % of claim and within the laboratory's stated specification of at least 90 %. The certificate's own note makes the distinction explicit: chromatographic purity "is not a measure of net peptide mass content". A reader who stopped at 99.99 % would miss that the vial holds 9.22 mg, not 10 mg.

How peptide identity may be established, and what HPLC purity alone cannot show

Purity tells you how much of the detected material is one compound. It does not tell you which compound. Identity is established separately, and certificates differ in how they do it:

Mass spectrometry, usually coupled to liquid chromatography, is the technique regulators and the analytical literature point to for confirming peptide identity and characterising peptide-related impurities; European guidance recommends at least two orthogonal identification methods and names LC-MS and peptide mapping among them ^[3][6]. When a certificate establishes identity only by retention time and UV spectrum, read the identity statement as consistency with the reference rather than as proof of sequence. The certificate wording matters: KMD states "Identity Conforms (RT + UV vs. reference)", which is exactly that.

Purity versus measured net content

These are the two numbers most often confused, and they answer different questions:

A peptide can be 99.99 % pure and still measure 9.22 mg in a 10 mg vial (the Thymosin Alpha-1 example). It can also measure above its label, as the GHK-Cu 100 mg certificate in our library does at 112.00 mg. Neither result contradicts the purity figure; they are different measurements.

Labeled amount versus the amount measured by the laboratory

The label claim is what the supplier intends to fill. The measured content is what the laboratory found in the sample it dissolved and analysed. Certificates express the comparison in one of two ways:

• As a percentage of claim with a specification, as KMD does: "9.22 mg (92.2 % of claim)" against "≥ 90 % of label claim". The result conforms because it clears the specification, not because it equals the label.
• As a measured value per component, as blend certificates do. The BPC-157 + TB-500 10 mg vial is labelled as 5 mg of BPC-157 plus 5 mg of TB-500. On the certificate below, Freedom Diagnostics reports each component separately: BPC-157 at 6.29 mg in vial 1 and 6.00 mg in vial 2 (mean 6.14 mg), and thymosin beta-4 at 6.74 mg and 6.23 mg (mean 6.49 mg). Each component is reported on its own, which is the only way to check that a blend contains both peptides in the expected proportion. The certificate prints no combined total and no specification column; the 12.63 mg shown in our COA Library for this certificate is the sum of the two component means (6.14 mg + 6.49 mg), recorded so that the library can show one net-content figure per entry.

The blend certificate (accession 2607200743, received July 20 and reported July 22, 2026, identity by LC-MS, purity by HPLC-UV) is also an example of a two-vial sample: it lists purity for vial 1 (99.15 %) and vial 2 (99.22 %) and reports 99.19 % as the result. When a laboratory tests more than one vial, the certificate normally shows the individual values and the mean; a spread between vials, such as 6.29 mg against 6.00 mg of BPC-157 here, is itself information about fill consistency. Two limits of this particular certificate are worth noting: it identifies the lot only by cap colour ("Red Cap"), and it reports results without a specification column, so the reader, not the certificate, judges them against the label.

Batch numbers, sample identification and traceability

A certificate is only useful if it can be tied to the vial in hand. Look for three identifiers:

1. The lot or batch number printed on the vial. Our 2026 lots carry identifiers of the form PPL-2611-TA10 (product and month) which appear on the certificate as "Client batch / lot".
2. The laboratory's own certificate or sample number, for example PPL-20261102-X2NF-01 (KMD), AX-2026-2696-CYB5 (Axiom) or accession 2607200743 (Freedom Diagnostics). This is the number to quote when verifying a certificate with the laboratory, and each of the four laboratories named in this article prints a verification address, code or search code on its certificates.
3. The sample description: form, cap and crimp colour, contents colour, seal condition, number of vials. Axiom's certificates photograph the vial as received and record "sealed, intact".

Some older certificates in our library identify the lot only by cap colour ("Red Cap", "White Cap") because the laboratory recorded what the client submitted and no batch number was supplied. Those certificates are still genuine reports on the sample tested, but they cannot be matched to a vial as precisely as a numbered lot can. We keep them in the COA Library with their original wording rather than editing them.

Testing dates and laboratory information

A certificate carries several dates, and they mean different things: the date the sample was received, the date it was analysed, and the date the certificate was issued or the data were sealed. Our COA Library lists the date each certificate was added to the library, which can be one or two days after the analysis date on the document. For record-keeping, use the analysis date from the certificate.

The laboratory should be named, with a way to verify the document. The certificates in our library come from independent laboratories that identify themselves and publish verification tools: KMD Analytical (kmdanalytical.com/verify), Axiom Analytics Laboratories (axiomanalyticslab.com, verification code on each certificate), Kovera Labs (koveralabs.com/verify, with an access code) and Freedom Diagnostics Testing (search code on each certificate). Each laboratory also states the limits of its work on the certificate itself; KMD, for instance, states that it is an independent testing laboratory and that it does not perform GMP release testing. We report those statements as written and make no claim about any laboratory beyond what its certificate says.

How to interpret specifications, results and testing methods

Every result on a certificate sits next to a specification. Reading them together answers three questions:

• Who set the specification? Some are compendial (USP <85> sets the method and the way endotoxin limits are expressed ^[7]); some are the laboratory's standard criteria; some are agreed with the client. KMD prints "SPEC SET IS CLIENT / METHOD-DEFINED" on its certificates, and Axiom labels each row "research screen", "validated in house" or "verified compendial". Those labels tell you how much weight the comparison carries.
• What does "conforms" or "PASS" mean? Only that the measured result met the specification shown. Axiom states this directly: a PASS "does not establish safety, efficacy, regulatory approval, legality, or suitability for human or animal use". A result can conform and still be worth noting, as 92.2 % of label claim is.
• Which method produced the result? The method determines what the number can mean. "HPLC, area %" is a chromatographic purity; "LC-MS" identity is a mass match; "kinetic chromogenic LAL, USP <85>" is a compendial endotoxin method. Validated methods are expected to have demonstrated specificity, accuracy and precision for their purpose ^[2]; a certificate rarely shows the validation data, but it should at least name the method and the detection conditions.

The Klow 80 mg certificate above (Axiom Analytics Laboratories, AX-2026-2696-CYB5, lot PPL-2610-KLOW, issued October 15, 2026) shows how much a fuller panel adds. For a four-component blend it reports identity by mass for each declared component, purity of 99.67 %, net peptide content as a mean of 83.45 mg over two vials with the range (83.37–83.53 mg), a container-to-container consistency check per component, a rapid-PCR sterility screen, endotoxin of 0.094 EU/mg by the USP <85> method against a stated house limit, an elemental impurities screen referenced to ICH Q3D ^[8], and a fentanyl screen. The same certificate labels which rows are compendial and which are research screens, and it states that unless the laboratory performed the sampling it does not attest that the sample represents the wider lot. That sentence applies to every certificate in our library.

Understanding chromatograms where supporting data is available

Most of our certificates reproduce the chromatogram. When you look at one, check four things:

1. One dominant peak at the stated retention time. The main-peak retention time on the certificate (6.899 minutes for the Thymosin Alpha-1 sample, 6.546 minutes for BPC-157 under the same laboratory's method) should match the peak you see.
2. Small peaks near the main peak. These are the related impurities that make up the difference between the purity figure and 100 %. Their size relative to the main peak is what the area percentage summarises.
3. The baseline. A flat baseline on either side of the peaks indicates a clean run; a rising baseline or broad humps can mean the method's gradient is still eluting material.
4. The detection wavelength and column. Kovera's certificate for the earlier Klow lot states "RP-HPLC, C18, DAD at 214 nm", which is the standard peptide-bond absorbance wavelength. Peak areas are only comparable between certificates that used comparable detection.

Limitations of laboratory testing and certificates

A certificate is strong evidence about one sample on one day. Its limits are worth stating plainly:

• Sample, not lot. Unless the laboratory drew the sample itself, the certificate describes the submitted vials. Fill variation between vials is not captured by a single-vial test, which is why two-vial certificates with a reported range are more informative.
• Tested parameters only. KMD's certificates state that no assessment was made of sterility, endotoxin, microbial, heavy-metal or residual-solvent content unless expressly noted. A purity certificate says nothing about those attributes.
• Client-supplied information. Label claim, lot number and sample identity are recorded as supplied by the client and are not independently verified by the laboratory.
• A point in time. Peptides degrade with heat, moisture and repeated freeze-thaw cycles. A certificate does not describe the material after storage and handling.
• No determination of suitability for any use. Every laboratory in our library states that its certificate is not a determination of safety or fitness for any purpose. Precise Pep Labs sells these materials for in vitro research use only, and nothing on a certificate changes that.

How to locate and interpret Precise Pep Labs' COA reports

Every active product's certificates are in the COA Library, grouped by product and size, newest first, with the reported purity and net content shown beside each entry and a "View COA" link to the laboratory's document. The current certificate is also linked from each product page, for example Thymosin Alpha-1 10 mg, Klow 80 mg and BPC-157 + TB-500 10 mg.

To read an entry: note the product and size, open the certificate, match the lot number on the certificate to the lot on your vial, then record the laboratory, certificate number, analysis date, purity, net content and method in your notebook. When a product has more than one certificate, the library keeps the earlier ones under "Previous COAs" so that lots can be compared; an older certificate describes an older lot, not the one currently shipping.

Articles in this library that cite a certificate pin it by its library record, so the figures shown here stay tied to the document they came from even after a newer lot is tested.

Common questions about COA verification

How can I confirm a certificate is genuine? Use the laboratory's verification page with the certificate or sample number printed on the document. KMD, Axiom and Kovera print a verification address or code on every certificate; Freedom Diagnostics prints a search code.

Why does the COA Library date differ from the date on the certificate? The library shows the date the certificate was added. The certificate shows when the sample was received, analysed and issued. Use the certificate's dates for records.

Why do two certificates for the same product show different numbers? Because they describe different lots, or different samples of a lot, tested at different times and sometimes by different laboratories with different methods. The Klow 80 mg entries in the library are an example: Kovera reported 99.881 % and 88.61 mg for a sample received in July 2026, and Axiom reported 99.67 % and 83.45 mg for lot PPL-2610-KLOW in October 2026.

What should I do if the lot on my vial is not in the library? Contact Precise Pep Labs with the lot number before using the material. The library is updated when a certificate is received, and a missing entry should be resolved before the lot is relied on.