How to Read a Peptide Certificate of Analysis

What is a certificate of analysis?

A certificate of analysis (COA) is a laboratory report stating the results of specified tests on a specified batch of material. For a research peptide it usually carries an HPLC purity percentage and a mass-spectrometry identity check, and sometimes a net peptide content figure; it is a record of a sample, not a guarantee about every vial sold under that name.

Supplier documentation shows the standard package. AAPPTec, a peptide manufacturer, states that the quality control documentation provided with every peptide includes mass spectral and HPLC analyses determining composition and purity, with amino acid analysis available on request. The same FAQ draws the line that matters for anyone injecting a research product: research-grade peptides are for laboratory use only and may not be used as drugs, while GMP active pharmaceutical ingredients are sterile products monitored for chemical and biological contaminants applicable to humans. A COA for a research-grade peptide documents the first category.

HPLC purity

Share of the chromatogram

The area of the main peak as a percentage of all peptide peaks detected.

Mass spectrometry

Identity check

The observed mass compared with the theoretical mass of the sequence.

Net peptide content

Share of the powder

The fraction of gross weight that is peptide; typically 50% to 90%.

Not on a typical COA

Sterility and endotoxin

Separate pharmacopoeial tests that research-grade documents rarely include.

How do you read the HPLC purity trace?

A chromatogram plots detector response against time. The sample is injected onto a reverse-phase column, its components separate by how strongly they stick to the column, and a UV detector records each one as it elutes. The target peptide is the main peak; everything else is an impurity peak. Purity is the area of the main peak divided by the total area of all peaks, as a percentage, so a 98.5% figure means the main peak was 98.5% of what the detector saw. AAPPTec describes the impurities as mostly incorrectly synthesized fragments and deletion sequences, incompletely deprotected peptides and residual water, and lists its purity tiers as 80% or greater, 90% or greater, 95% or greater and 98%, with most catalog peptides at 95% or above and labile sequences, such as those with a free cysteine, lower.

Three things do not appear in that number: water and salts are invisible to the UV detector, so they do not reduce purity; any peptide that elutes with the main peak is counted as the main peak; and the figure belongs to the injected sample, not to the vial on the shelf.

How do you read the mass-spectrometry identity page?

Mass spectrometry answers a different question: is the main peak the right molecule? The instrument ionizes the sample and measures mass-to-charge ratio, and the report compares the observed mass with the theoretical molecular weight of the sequence. Peptides often appear as multiply charged ions, so a report may list [M+2H]2+ or [M+3H]3+ peaks whose values are converted back to the neutral mass. Sodium and potassium adducts, [M+Na]+ and [M+K]+, are also common and normal; the AAPPTec FAQ attributes them to the water and buffers used in purification and notes they can never be removed completely.

The theoretical masses come from the structure, and the compound pages carry them. Ipamorelin is 711.9 g/mol; BPC-157 is 1419.5 g/mol; CJC-1295 without DAC is 3367.9 g/mol and CJC-1295 with DAC is 3647.2 g/mol. That last pair is the clearest example of what the identity page is for: the two molecules differ by about 279 g/mol, the extra lysine and its maleimidopropionyl group, and a mass spectrum resolves that difference without difficulty. In 2010 a Norwegian doping laboratory ran liquid chromatography with high-resolution tandem mass spectrometry on an unknown preparation submitted by police and customs, found a 29-residue peptide with a C-terminal amide, and reconstructed from the fragmentation data a sequence matching the product marketed as CJC-1295: the no-DAC molecule. A matching mass is strong evidence of identity. A mismatched one, or a spectrum whose main ion does not correspond to the label, means the vial is not what it says.

What is the difference between HPLC purity and net peptide content?

Purity describes the peptide fraction; net peptide content describes the powder. The gross weight on a label, say 5 mg, is what the vial weighed in. That powder is not all peptide. Synthetic peptides come off the purification column as salts, usually trifluoroacetate (TFA) or acetate, with a counter-ion attached to the N-terminus and to every arginine, lysine and histidine, and the lyophilized solid holds bound water and traces of solvent. Net peptide content is the percentage of the gross weight that is actually peptide. AAPPTec puts the typical range at 50% to 90%; AmbioPharm says 60% to 90%. Both state that content and purity are independent measurements: a 99% pure peptide can still be 75% peptide by weight.

AAPPTec gives the theoretical calculation. For a 1,000 g/mol peptide with a free N-terminus and one arginine, two TFA counter-ions of 114 g/mol each are needed, so the theoretical content is 1,000 ÷ (1,000 + 2 × 114) = 81%, before any water is counted. A 5 mg gross vial at 80% net peptide content and 99% purity holds 5 × 0.80 × 0.99 = 3.96 mg of the target peptide. Reconstituted with 2 mL it is 1.98 mg/mL rather than 2.5 mg/mL, and a 10-unit draw carries about 198 mcg rather than 250 mcg. The calculator takes whatever mass is entered: if a COA reports net peptide content, gross mass multiplied by that content is the figure that describes the peptide, and if it does not, the label mass is an upper bound. Most research COAs do not report net peptide content, which requires amino acid analysis, elemental analysis or UV spectrophotometry rather than the HPLC and mass-spec pair.

What can a certificate of analysis not tell you?

A COA is a chemistry document about a sample, and four things sit outside it. Sterility: whether the vial is free of viable microorganisms is established by the sterility test of USP chapter 71, a separate test that research-grade documentation rarely includes. Endotoxin: bacterial endotoxins, which cause fever when injected, are measured by the test of USP chapter 85; the pharmacopoeial standard for sterile water for injection, for example, is fewer than 0.25 endotoxin units per mL, and a research COA with no endotoxin line has shown nothing about this. Provenance: a COA describes the batch a laboratory received, which may be a manufacturer lot that a reseller divided into vials months later, so the link between the document and the vial in hand depends on a lot number that matches and a chain of custody that holds. Fill weight: an HPLC trace says nothing about whether the vial contains 5 mg or 4 mg; that is a separate gravimetric measurement.

An independent laboratory test of a blend vial recorded in the compound library illustrates the point from the favorable side: a laboratory found 9.932 mg against a 10 mg label at 99.56% purity, and the report notes that no sterility or heavy-metal screen was performed. Even a good result covers only what was measured.

What has independent testing of internet-sold compounds found?

The most rigorous published test of this supply chain concerns SARMs rather than peptides, but the products were bought the same way. In a 2017 JAMA analysis, researchers searched the web between February and March 2016, purchased 44 products marketed as selective androgen receptor modulators, and analyzed them under chain-of-custody and WADA-approved procedures. Only 23 of the 44 (52%) contained a SARM at all. Another 17 (39%) contained a different unapproved drug, including the growth hormone secretagogue ibutamoren, the PPAR-delta agonist GW501516 and the Rev-ErbA agonist SR9009. No active compound was detected in 4 products (9%); substances not listed on the label were present in 11 (25%); the amount of active compound matched the label in only 18 (41%); and the stated amount differed substantially from the measured amount in 26 (59%). The cardarine and LGD-4033 pages carry the same study because both compounds turned up in it.

For peptides specifically the record is thinner but points the same way: the 2010 Norwegian report identified a seized preparation as the no-DAC peptide sold under the CJC-1295 name, and community-run testing services publish vial-by-vial purity and mass results that vary by vendor and batch. None of this is evidence about any particular vial; it is evidence that the label is a claim, and that a COA, read properly, is the only document between the claim and a measurement.

What this guide does not establish

This article does not establish that any vendor, product or certificate is trustworthy, nor that a clean COA makes a research peptide safe to inject; it explains what each line on the document measures and what no line on it can. The molar masses quoted here are on the compound pages with the PubChem records they come from, the full compound library lists the same data for every entry, and the storage guide covers what happens to a tested vial after water is added. The calculator converts the label mass into volumes, and it will do so just as readily for a mass that was never verified.