What Testing Methods Appear on a Peptide Certificate of Analysis

A certificate of analysis, usually shortened to CoA, is the lab document a peptide listing points to as proof of what is actually in the vial. The testing methods that appear on a peptide certificate of analysis generally fall into a few groups: confirming the molecule’s identity, measuring its purity, checking for contaminants that should not be present, and recording physical properties like appearance and mass. Knowing what each method checks makes it easier to read a CoA critically rather than treating the presence of a document as proof on its own.

What a Certificate of Analysis Actually Documents

A CoA is a batch-specific lab report, not a general product spec sheet. It should carry a lot number, a test date, and a set of results tied to that specific production run. When a listing links a CoA that has no batch number, or that reads identically across multiple different products, the document is functioning as decoration rather than as batch-level evidence. The testing methods themselves are what give the report its substance, so it helps to know what each one is actually checking for.

Identity Testing: Confirming the Molecule

Identity testing answers a narrow question: is this peptide the sequence it claims to be, and not a different compound entirely. The two methods that show up most often for this purpose are mass spectrometry and amino acid analysis.

Mass spectrometry measures the molecular weight of the peptide and compares it against the expected weight for the correct amino acid sequence. A result that lands close to the calculated mass supports the identity claim; a result that is noticeably off suggests a synthesis error, a truncated sequence, or an entirely different substance. Amino acid analysis works differently, breaking the peptide down into its component residues and confirming that the ratio of amino acids present matches what the sequence predicts. Some CoAs also list a high-performance liquid chromatography, or HPLC, retention time as a secondary identity marker, since a known peptide should elute from the column at a consistent, reproducible time under fixed conditions.

Purity Testing: HPLC and Related Assays

Purity testing is where HPLC does most of the work. The method separates the contents of a sample by passing it through a column, and a detector records each compound as a peak on a chromatogram. The peptide’s own peak is compared against the total area of all peaks in the run, which produces a purity percentage. A listing describing “98% purity by HPLC” is describing exactly this calculation: the target peptide’s peak area as a proportion of everything the detector picked up, including truncated sequences, deletion products, and residual reagents left over from synthesis.

Some certificates supplement HPLC with mass spectrometry-based purity confirmation, running the sample through a combined LC-MS system that separates and identifies each peak rather than just measuring its size. This catches impurities that happen to co-elute at the same retention time as the main peptide peak but would otherwise go unflagged by HPLC alone.

Testing for What Shouldn’t Be There

A separate category of testing methods on a peptide certificate of analysis looks for contamination rather than confirming the peptide itself. Endotoxin testing, most commonly run as a Limulus Amebocyte Lysate (LAL) assay, measures bacterial endotoxin levels, which is a standard check for materials associated with any injectable-grade research context. Bioburden or sterility testing checks for viable microorganisms in the sample. Residual solvent testing, often done by gas chromatography, screens for leftover organic solvents from the synthesis and purification process. None of these methods say anything about the peptide’s identity or purity — they exist to catch different failure modes, which is why a thorough CoA lists them as separate line items rather than folding them into the purity result.

Physical and Compositional Checks

Beyond identity, purity, and contamination, a CoA often records simpler physical data: appearance (typically a white to off-white lyophilized powder), and water content, measured by Karl Fischer titration. Water content matters because residual moisture affects both the peptide’s measured mass and its long-term stability, so a listing’s stated peptide content assumes the water percentage reported on the CoA is accurate. Some certificates also include a trifluoroacetic acid (TFA) content figure, since TFA is used as an ion-pairing agent during HPLC purification and can remain in trace amounts in the final product.

Common Testing Methods at a Glance

Testing method	What it checks	Typical CoA line item
Mass spectrometry	Molecular weight vs. expected sequence mass	Identity confirmation
Amino acid analysis	Ratio of residues in the sequence	Identity confirmation
HPLC	Peak area of target peptide vs. total peaks	Purity percentage
LC-MS	Peak identity plus peak size	Purity confirmation
LAL assay	Bacterial endotoxin level	Endotoxin testing
Gas chromatography	Leftover synthesis solvents	Residual solvent testing
Karl Fischer titration	Moisture content of the lyophilized powder	Water content

Reading a Certificate of Analysis Against the Listing

The most useful check a reader can do is match the lot number on the CoA to the lot number, if any, printed on the vial or listed on the product page. A CoA without a lot number, or one dated years before the listing went live, cannot be verified against the specific batch being described. A supplier’s BPC-157 product listing, for instance, ties its certificate of analysis to a specific batch number, which is the detail that lets a reader confirm the document corresponds to the actual vial rather than a generic manufacturer template reused across every batch. It is also worth checking whether the CoA names the testing method for each result, rather than just stating a number — a purity figure with no method attached gives no way to judge how it was measured or how reliable the number is. Readers comparing listings across the broader research peptide catalogue will notice that suppliers vary widely in how much of this testing detail they disclose alongside a product.

Summary

The testing methods that appear on a peptide certificate of analysis break down into identity checks (mass spectrometry, amino acid analysis), purity checks (HPLC, LC-MS), contamination checks (endotoxin, bioburden, residual solvent testing), and physical checks (appearance, water content). A complete CoA ties these results to a specific batch number and names the method behind each figure, which is what turns the document from a marketing attachment into something that can actually be evaluated.