How to Verify Research Peptide Purity (COA, HPLC, MS) 2026

For in-vitro laboratory research use only. Not for human consumption.

For examples of the documentation format described below, see the Certificates of Analysis published for GHK-Cu and GHRP-6.

Analytical documentation is the only objective way to evaluate a synthetic peptide. A purity figure printed on a label or a product page is only as credible as the analytical chemistry behind it: without the underlying chromatogram and identity data, the number cannot be checked, and two products carrying the same headline figure may be very different materials.

This guide walks through the four documents that, together, characterize a peptide sample: the Certificate of Analysis (COA), the HPLC chromatogram, the identity result (a mass spectrum or an FTIR spectrum), and the testing laboratory's details. By the end you'll be able to evaluate any supplier's documentation against the same analytical criteria used throughout peptide chemistry.

Why analytical characterization matters in laboratory research

Synthetic peptides are produced by solid-phase peptide synthesis (SPPS). The process is iterative — amino acids are coupled one at a time onto a growing chain — and every coupling step has a yield below completion. Truncated sequences, deletion sequences, and incompletely deprotected intermediates accumulate as impurities. The final crude product is then purified, typically by reverse-phase HPLC, before being lyophilized and vialed.

The purity figure on a COA reflects how successful that purification was. Common impurity classes include truncated sequences, deletion sequences, oxidation products (particularly on methionine, tryptophan, and cysteine residues), trifluoroacetic acid (TFA) counter-ion residues, acetate or formate counter-ions, and residual solvents such as acetonitrile and water.

For in-vitro work, the impurity profile matters because impurities can interfere with binding assays, alter apparent receptor activity, and confound experimental data. A sample containing a measurable fraction of truncated sequence is a different experimental input from a sample in which the target peptide accounts for nearly all of the integrated peak area.

The Certificate of Analysis (COA): what it typically contains

A Certificate of Analysis summarizes the analytical testing performed on a sample of a product. The information a complete COA typically contains:

Product name and sequence — the full amino acid sequence in one-letter or three-letter code
Batch or lot identifier — the production reference the tested sample came from
Test date — when the analysis was performed
Molecular formula and molecular weight — theoretical, calculated from sequence
Appearance — typically "white to off-white lyophilized powder"
HPLC purity — with the chromatogram attached or referenced
Identity confirmation — LC-MS (observed mass vs. theoretical mass) or FTIR (spectral match to a reference)
Counter-ion content — TFA, acetate, etc.
Water content — by Karl Fischer titration
Testing laboratory — name and location of the lab that performed the analysis

A COA that lists purity as a single number without an attached chromatogram is a summary, not the underlying evidence. The chromatogram and the identity data are what allow a reader to check the number and understand the impurity profile behind it.

Warning signs on a COA

The document names a different compound or sequence than the product it accompanies
The identity result is missing, or does not match the stated compound (for LC-MS, an observed mass that disagrees with the theoretical mass)
The testing laboratory is unnamed
Only HPLC is reported (no identity confirmation), or only an identity result (no HPLC)
The document is an image with a summary number and no analytical data attached

Reading an HPLC chromatogram

High-Performance Liquid Chromatography (HPLC) separates the components of a sample by passing them through a column packed with a stationary phase under high pressure. Different molecules elute (exit the column) at different times depending on their interaction with the stationary phase and mobile phase. The detector records absorbance over time, producing a chromatogram — a plot of detector signal vs. retention time.

For peptide analysis, the standard method is reverse-phase HPLC (RP-HPLC) using a C18 column with a water/acetonitrile gradient containing trifluoroacetic acid as an ion-pairing agent, with UV detection at 214 nm or 220 nm (the peptide-bond absorbance).

What a clean chromatogram looks like

One dominant peak representing the target peptide
Baseline noise that is flat and low relative to the main peak
Small impurity peaks before or after the main peak, each small relative to the main peak
Peak shape — symmetrical, with sharp rising and falling edges (no significant tailing)

How HPLC purity is calculated

Purity by HPLC is calculated as the integrated area of the target peak divided by the total integrated area of all detected peaks, expressed as a percentage (area percent). In the chromatogram of a highly purified sample, a single dominant peak accounts for nearly all of the integrated area and impurity peaks are barely distinguishable from baseline. In a less purified sample, one or more impurity peaks are clearly visible and account for a correspondingly larger share of the total area.

Common mistakes when reading a chromatogram

Reading peak height instead of peak area. Tall, narrow peaks can have less area than short, broad peaks. Purity is calculated from area.
Ignoring the y-axis scale. Impurity peaks that look small may be substantial if the y-axis is heavily zoomed on the main peak.
Not checking the gradient. A poorly chosen gradient can fail to separate closely related impurities, inflating the apparent purity number.

Identity confirmation: mass spectrometry and FTIR

HPLC tells you how much of the sample is the main component. An identity test tells you what that component is. HPLC plus identity confirmation (LC-MS or FTIR) is the minimum for peptide characterization.

The most common techniques for peptide characterization are ESI-MS (electrospray ionization mass spectrometry) and MALDI-TOF (matrix-assisted laser desorption/ionization time-of-flight). Both ionize the peptide and measure the mass-to-charge ratio (m/z) of the resulting ions, allowing the observed molecular mass to be calculated and compared to the theoretical mass derived from the sequence.

Reading a mass spectrum

Observed mass vs. theoretical mass — should agree within the tolerance of the instrument used (commonly within one to a few daltons for a typical synthetic peptide)
Charge states — ESI typically produces multiple charge states (e.g., [M+H]⁺, [M+2H]²⁺, [M+3H]³⁺)
Sodium and potassium adducts — common, expected, not a quality issue (roughly +22 or +38 Da above the protonated mass)

What a mass spec discrepancy means

Observed mass lower by the mass of one amino acid residue — a deletion sequence, suggesting an incomplete coupling
Observed mass exactly 16 Da too high — oxidation (commonly on methionine)
Observed mass significantly different — wrong sequence, wrong peptide, or major impurity

If the observed mass on the COA does not match the theoretical mass from the published sequence, the documentation does not confirm identity, regardless of what the HPLC chromatogram shows.

FTIR as an identity method

Fourier-transform infrared spectroscopy (FTIR) is the other identity method commonly reported on peptide COAs. It measures how the sample absorbs infrared light, producing a spectrum shaped by the peptide backbone (the amide I and amide II bands) and by side-chain functional groups. The laboratory compares that spectrum with a reference spectrum for the compound and reports identity as confirmed when they match. FTIR does not give a molecular mass, so it cannot size a deletion sequence the way MS can, but paired with HPLC it confirms that the material is the stated compound. Freedom Diagnostics Testing, the laboratory that tests every Excalibur Peptides product, reports identity by LC-MS.

Third-party testing: what it means

"Third-party tested" is a common phrase in this category. To be meaningful, third-party testing typically satisfies three conditions:

The testing laboratory is named on the COA. An anonymous attestation cannot be checked.
The laboratory is independent of the manufacturer. Same parent company, same ownership, same physical address — not third-party.
The laboratory performed the analyses reported. HPLC and identity data (LC-MS or FTIR) require the instruments that produce them.

A complete COA lists the testing laboratory's name and address and, often, its accreditation. ISO/IEC 17025 is the international standard for the competence of testing and calibration laboratories.

Where to get peptides tested independently

Researchers who want to check a supplier's documentation independently can submit a sample to a contract analytical laboratory. Several categories of US-based options exist:

University-affiliated mass spec cores — many research universities operate fee-for-service mass spectrometry facilities
Independent analytical labs — fee-for-service HPLC and MS, often used for academic and biotech work
ISO/IEC 17025-accredited contract laboratories — accredited for specific methods, typically at higher cost

An independent analysis of a retained sample is a reasonable one-time check whenever documentation is in doubt.

A worked example: reviewing the COA for a vial of BPC-157

Suppose a vial of BPC-157 arrives in the laboratory. To review its documentation:

Locate the supplier's published COA. Check whether a Certificate of Analysis is publicly accessible from the product page or a COA database before purchase, rather than only on request.
Record the identifiers. Note any batch or lot identifier on the COA and the identifier printed on the vial label, and keep both with your laboratory records.
Check the identity result. BPC-157 (the 15-residue sequence GEPPPGKPADDAGLV) has a molecular weight of approximately 1419.5 g/mol (average mass). If the COA reports LC-MS, the observed mass should agree with this within the instrument's tolerance; if it reports FTIR, identity is stated as a spectral match to the reference. The BPC-157 COA published by Excalibur Peptides, issued by Freedom Diagnostics Testing, reports identity by LC-MS.
Inspect the HPLC chromatogram. Look for one dominant peak, flat baseline, and small impurity peaks. The reported purity should reflect what you see in the chromatogram.
Confirm the laboratory. The lab name should be present, distinct from the manufacturer, and ideally accredited for the methods reported.

If all five checks are satisfied, the documentation supports the identity and composition stated for the product. If any one is missing, the documentation is incomplete, and it is reasonable to ask the supplier for the missing data.

Frequently asked questions

What purity is acceptable for research peptides?

There is no single universal threshold. The appropriate specification depends on the experiment: quantitative binding and receptor assays are more sensitive to impurities than qualitative or exploratory work. Rather than relying on a headline figure, review the HPLC chromatogram and identity result (LC-MS or FTIR) on the product's Certificate of Analysis and decide whether the impurity profile is acceptable for the assay you are running.

How is HPLC purity calculated?

As the integrated area of the target peak divided by the total integrated area of all detected peaks, expressed as area percent. The calculation depends on the detection wavelength, the gradient, and the column, which is why the chromatogram should accompany the number.

Can I rely on a purity figure that has no chromatogram?

No. A purity number without an attached chromatogram is an unverified claim. The chromatogram is the underlying evidence; without it, there is no way to confirm how the purity was calculated, what the impurity profile looks like, or whether the analytical method was appropriate.

What does third-party testing mean for peptides?

Third-party testing means an independent analytical laboratory — one not owned by or affiliated with the manufacturer — has run HPLC and an identity test (LC-MS or FTIR) on a sample and issued a report naming the laboratory. HPLC quantifies the target peptide relative to impurities; identity testing confirms the molecule is the one claimed. Independence removes the conflict of interest inherent in self-reported data.

How do I read a peptide COA?

Confirm the compound name and sequence, check that the identity result (an LC-MS mass match or an FTIR spectral match) confirms the compound, inspect the HPLC chromatogram for one dominant peak with small impurity peaks, note any batch or lot identifier for your records, and confirm the testing laboratory is named and independent from the manufacturer.

Where can I get peptides tested independently?

University-affiliated mass spec cores, independent analytical labs offering fee-for-service HPLC and MS, and ISO/IEC 17025-accredited contract testing laboratories all accept outside samples. A single independent analysis is a reasonable check if a supplier's documentation is in doubt.

Where can I look up Excalibur Peptides' COAs?

All 18 products are third-party tested; each product's Certificate of Analysis is published on its product page and in our COA database, with the testing laboratory named on each report.

How to Verify Research Peptide Purity: COAs, HPLC & Mass Spec Explained