GLP Peptide Content Accuracy: Verifying a Label Claim on a Research COA

A label claim on a research vial makes two separate assertions, and a purity percentage tests neither of them completely. The first assertion is identity: that the molecule inside is the peptide named on the label, which is demonstrated by mass spectrometry comparing an observed mass against a theoretical mass. The second is content: that a stated number of milligrams of that peptide is present, which is demonstrated only by a quantitative assay run against a reference standard. HPLC purity is an area-percent figure and answers a third, narrower question - what fraction of the integrated peak area was the target. Published analysis of GLP-class vials bought from illegal no-prescription sellers showed how far those numbers can decouple: measured content ran 28.56% to 38.69% above the labelled amount while measured purity was 7.70% to 14.37% against a 99% label claim. The practical test for a reader is narrow: can you obtain a batch-specific third-party report that states an observed mass and an assayed milligram content, and can you confirm that report with the issuing laboratory rather than with the seller?

Published 2026 - For research use only (RUO). Nothing here is medical advice, a dosing protocol, or a human-use recommendation. This page is about analytical verification of label claims on research-use material and nothing else.

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Purity is not content: why most label claims are untested

Almost every certificate circulating in this market leads with a purity number. That number is usually real and usually measured. It does not mean what the listing implies it means.

HPLC purity is an area-percent figure. The detector integrates the peaks it sees and reports the target peak as a fraction of total integrated peak area. It answers “of the material that eluted and absorbed at the detection wavelength, how much was the target?” It does not answer “how much material is in this vial?” Those require different experiments.

Three distinct concepts sit between an area-percent number and a milligram claim:

Concept	What it measures	What it cannot tell you
Chromatographic purity (area %)	Target peak area as a fraction of total integrated peak area	Absolute quantity; anything that does not absorb at the detection wavelength
Net peptide content	Weight fraction of the lyophilized powder that is actually peptide	Whether that peptide is the correct one
Assay / content (mg per vial)	Absolute mass of target peptide, quantified against a reference standard	Sterility, endotoxin, or non-peptide contaminants

Bachem’s quality-control guidance defines net peptide content as “the percentage of peptides relative to non-peptidic material (mostly counterions and moisture),” notes that most peptides carry trifluoroacetic or acetic acid bound as the salt, and states plainly that “NPC and purity are not equivalent, because the former includes peptidic contaminants” [1]. Lyophilized material also carries residual water, determined by Karl Fischer titration rather than inferred from a chromatogram [1].

So a vendor can be literally truthful with “99% HPLC purity” and still ship a vial whose milligram claim has never been tested by anybody. The two statements are compatible. Our COA glossary defines each term individually; the point here is what happens when only one of the three is ever reported.

What independent testing of GLP-class vials showed

In November 2024 researchers published a multi-method market-surveillance study in the Journal of Medical Internet Research that mapped illegal no-prescription online sellers of GLP-class product, made test purchases, and analysed what arrived by liquid chromatography with mass spectrometry, plus sterility and bacterial endotoxin testing [2].

The scale is worth stating because it establishes what the sample is. The team evaluated 1,080 search-engine result links, identified 134 links leading to 59 unique illegal online pharmacy sites, and placed six test purchases. Three arrived as vials. Three prefilled-pen orders never arrived at all - straightforward non-delivery, before any analytical question arises.

The published findings on the three delivered vials [2]:

Measurement	Result
Content vs label claim	28.56% to 38.69% above the labelled amount
Purity measured vs 99% claimed	7.70% to 14.37%
Sterility	No viable microorganisms detected in any sample
Bacterial endotoxin	Detected in every sample, 2.1645 to 8.9511 EU/mg
Packaging and labelling inspection	59% to 63% non-compliance against a standardised checklist

Two things follow, and the second is the one this article exists for.

First, the direction of the content error. Every delivered sample was over the label, not under it. The common assumption that gray-market vials are simply underfilled is not what this dataset showed. Overfill is the same defect as underfill - an uncontrolled process that nobody measured - and it is equally invisible without a quantitative assay.

Second, the decoupling. Content ran above label while purity ran roughly an order of magnitude below the claim. Those two facts can only coexist if the vials held far more total powder than the label implied, with the target peptide a small minority of that mass. Read that as arithmetic rather than as a reported figure: it is what a high content result and a single-digit purity result jointly require. A buyer checking only “is there enough peptide in the vial” would have passed those samples. A buyer checking only purity would have had no idea how much peptide was there.

For the wider picture of how often analysed peptide products miss their label across published studies, we keep that evidence in a separate piece on what independent testing shows about failure rates. This page is narrower: it is about the two measurements that make a label claim checkable in the first place.

Regulators describe the same failure mode in blunter language. FDA states that counterfeit and illegally marketed versions of these products “could contain the wrong ingredients or harmful ingredients” and “could contain too little, too much or no active ingredient at all” [3]. The agency has also stated that salt forms of a GLP-class active ingredient “are different active ingredients than are used in the approved drugs” [3] - which is a naming problem as much as a chemistry one, because a certificate that prints a compound name with no observed mass and no stated counterion has not resolved which material was assayed.

The four checks that answer the label-claim question

Reduced to what you can do with a PDF open in front of you.

1. Confirm identity by observed mass, not by the name in the header. The report should state an observed mass from a mass-spectrometry experiment and compare it to a theoretical value for the intended sequence. Theoretical masses for common research peptides are public and we tabulate them in our molecular weight reference. If a report names a peptide but shows no mass, identity has been asserted, not demonstrated. A name in a header is typed by a human; an observed mass is produced by an instrument.

2. Find the milligram number, or conclude there is not one. Search the document for a quantitative result expressed in mg or mg per vial, with a named method and a named reference standard. “99.6% purity by HPLC” is not that number. If no milligram figure appears anywhere in the report, the label claim has not been tested, and no amount of chromatogram detail changes that. This is also why cross-vendor price comparison is close to meaningless without it - our cost-per-mg calculator normalises listings to a per-milligram figure, but the output is only as honest as the milligram number you feed it.

3. Match the batch, not the product. A report is evidence about one batch. Check that the lot or accession identifier on the report matches the vial in hand, and that the test date is plausibly close to the manufacturing date. A certificate issued for a product line rather than a batch is marketing collateral wearing a lab coat.

4. Verify with the laboratory, not with the seller. This is the step that separates checkable evidence from a PDF anyone can edit in a browser. If the issuing laboratory publishes an accession lookup, use it, and confirm the numbers on the seller’s copy match the laboratory’s own record. A certificate hosted only on the seller’s domain has a single point of failure, and that point is the party with the financial interest. The mechanics are in our COA lookup walkthrough.

One further item is worth flagging even though it is not a content-accuracy check: endotoxin and sterility are separate assays that a purity-and-content report does not cover. The surveillance data above is unambiguous on this - every sample was free of viable microorganisms and every sample carried detectable endotoxin [2]. Those are independent questions, treated on their own terms in our endotoxin and sterility guide.

Scope of testing: the failure mode nobody audits

The criteria below hold up when applied adversarially, and most vendors in this category fail them.

Criterion	Passing evidence	What a failure looks like
Third-party, not in-house	Report on the testing laboratory’s letterhead, laboratory independently identifiable	Unbranded PDF, or a “lab” with no traceable corporate existence
Batch-linked	Lot or accession ID printed on both report and vial	One undated report reused across a whole product line
Identity demonstrated	Observed mass reported and compared to theoretical	Compound name in the header only
Content quantified	Assay in mg against a named reference standard	Area-percent purity presented as if it were content
Independently verifiable	Accession lookup hosted by the laboratory, not the seller	PDF available only from the vendor’s own server
Scope stated honestly	Vendor says which SKUs are tested and which are not	Blanket “all products third-party tested” with four PDFs on the site

That last row is where most of the deception in this market actually lives, and it is the one nobody checks. Outright forged reports are rare. What is common is a genuine report for one SKU presented so that it implies coverage of a catalogue. The audit is arithmetic: count the distinct batch reports, count the SKUs, compare the two numbers. If the second is larger than the first, the difference is untested and should be treated that way.

Two related notes on labelling integrity. FDA has issued warning letters to online sellers of unapproved GLP-class products that were labelled “for research purposes” or “not for human consumption” while the sellers’ own websites established that the products were intended as drugs for human use [3][4]. A peer-reviewed commentary in Annals of Pharmacotherapy documented the same use of research-only framing as a supply-chain workaround [5]. The relevance to vetting is direct and it is not a legal aside: a vendor whose RUO labelling is genuine does not pair it with consumer-facing use instructions. One that does has told you something about how it treats every other claim printed on the site, including the number on the label.

How Pepora scores

Applying the grid above to peporalabs.com, including the part that does not score well.

What is verifiable. Four products carry batch-specific third-party certificates from Freedom Diagnostics, a US laboratory, run by HPLC with UV and mass spectrometry, each with an accession number that can be looked up on the laboratory’s own site rather than only on the store’s [6]:

Product	Reported purity	Freedom Diagnostics accession
GHK-Cu	99.98%	Pepo2603130126
Tesamorelin	99.348%	Pepo2603130125
TB-500 (Thymosin Beta-4)	99.699%	Pepo2603130123
GLP-3 RT	99.67%	Pepo2603130122

That combination clears the checks most of this market fails: an independent laboratory, a batch-linked accession, mass-spec identity alongside the purity figure, and verification hosted by the laboratory rather than the vendor.

The caveat, stated plainly. Four accessions is four accessions. Pepora’s catalogue also includes BPC-157, Epitalon, Thymosin Alpha-1, ARA-290 and the KLOW, Glow and Wolverine blends, and those do not carry a Freedom Diagnostics report of the kind listed above. For any of them the honest position is that the label claim is not independently documented in the same way and should not be treated as though it were. Ask before assuming, and do not let four good certificates imply coverage of eleven products. That is precisely the failure mode described in the table above, and it applies here as much as anywhere.

What the reports do not cover. None of these certificates address sterility or endotoxin, which the surveillance data shows are independent failure modes [2]. A purity-and-identity certificate is one layer of evidence, not a clean bill of anything.

The disclosed pick

FAQ

Does a 99% purity COA mean the vial contains the labelled milligrams? No, and this is the single most misunderstood point in the category. HPLC purity is an area-percent figure: it describes what fraction of the integrated peak area is the target peptide, relative to other peaks. It says nothing about how much material is in the vial. Lyophilized peptides also carry water and counterion mass, so gross powder weight overstates net peptide. Purity and content are two different measurements and a complete report needs both.

What is the difference between identity and content on a COA? Identity asks whether the molecule in the vial is the peptide named on the label, and it is answered by mass spectrometry comparing an observed mass against a theoretical mass. Content asks how many milligrams of that peptide are present, and it is answered only by a quantitative assay against a reference standard. A report can demonstrate one and not the other. A compound name typed into a header demonstrates neither.

What did independent testing of gray-market GLP-class vials actually find? A 2024 market-surveillance study in the Journal of Medical Internet Research (PMID 39509151) test-purchased from illegal no-prescription online sellers. Three vials were delivered and three prefilled-pen orders never arrived. In the delivered vials, measured content exceeded the labelled amount by 28.56% to 38.69%, while measured purity was 7.70% to 14.37% against a 99% label claim. Endotoxin was detected in every sample, from 2.1645 to 8.9511 EU/mg.

Why does over-label content matter as much as under-label content? Because both are the same underlying defect: nobody measured. The published gray-market data ran over the label, not under it, which contradicts the common assumption that the risk is only underfill. An unmeasured vial can deviate in either direction, and no amount of chromatogram detail reveals which. Only a quantitative assay figure expressed in milligrams makes the label claim checkable at all.

What is the salt-form problem and does it show on a COA? Synthetic peptides are usually isolated as salts, most often trifluoroacetate from reverse-phase purification, and the counterion is part of the powder mass. FDA has stated that salt forms of a GLP-class active ingredient are different active ingredients than are used in the approved drugs. A mass-spectrometry trace can distinguish the peptide itself, but a report that lists only a compound name with no observed mass and no stated counterion leaves the question open.

How much variance from a label claim is normal? Pharmacopeial monographs for finished products commonly specify an assay window near 90 to 110 percent of label claim, and independent peptide laboratories often report against a wider tolerance band. The number matters less than whether a number exists at all. A batch report stating an assayed milligram content with a named method and a named reference standard is checkable. A report carrying only a purity percentage cannot be checked against the label claim in any direction.

References

1. Bachem. Quality Control of Amino Acids and Peptides: A Guide (net peptide content, counterion and moisture). https://www.bachem.com/knowledge-center/quality-control-of-amino-acids-peptides-a-guide/
2. Ashraf AR, Mackey TK, Vida RG, Kulcsár G, Schmidt J, Balázs O, Domián BM, Li J, Csákó I, Fittler A. Multifactor Quality and Safety Analysis of [GLP-1 Receptor Agonist] Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. J Med Internet Res. 2024;26:e65440. PMID 39509151. DOI 10.2196/65440. https://pubmed.ncbi.nlm.nih.gov/39509151/ (One generic drug name in the original title is redacted to category language for compliance; the PMID and DOI resolve to the unaltered record.)
3. US Food and Drug Administration. FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. FDA Drug Alerts and Statements. https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
4. US Food and Drug Administration. Warning Letter, GLP-1 Solution, WL #715883, 9 September 2025. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/glp-1-solution-715883-09092025
5. Belcourt J, Ly P, White CM. Bypassing Prescribers and Pharmacists: Online Purchasing of [GLP-1 Receptor Agonists] “For Research Purposes”. Ann Pharmacother. 2025 May;59(5):485-490. PMID 39285774. https://pubmed.ncbi.nlm.nih.gov/39285774/ (Two generic drug names in the original title are redacted to category language for compliance; the PMID resolves to the unaltered record.)
6. Freedom Diagnostics Testing. Certificate of Analysis lookup by accession number. https://freedomdiagnosticstesting.com/search-for-your-coa-based-on-the-unique-accession-number/

coaindex is a Pepora affiliate (peporalabs.com) and earns a commission on purchases made with the code above. This is affiliate education, not journalism, and it ranks vendors on checkable, independently verifiable third-party-COA criteria. Research use only. Not for human or veterinary use, and nothing here is medical advice.