Peptide Testing Explained: Purity, Identity & COA

A clear guide to the lab methods used to check peptide identity, purity, and fill weight.

What Is Peptide Testing?

Peptide testing is the lab analysis of a peptide sample used to verify three key traits: identity (is the peptide what the label claims?), purity (how much of the vial is the target peptide vs. other material?), and fill weight (how much material is in the vial?). These three checks help researchers trust that the sample meets spec and is fit for research.

This kind of analysis of peptides is common in peptide research and testing peptides for lab use. The same workflow can also help with diagnostic peptides. PepsReview offers free peptide testing with HPLC and LC-MS. It is a lab service, not a peptide testing kit. An outside lab runs the tests, and results arrive in 5-7 business days. Request a free test here.

The Peptide Testing Process: Step by Step

  1. Sample receipt: Your peptide sample, usually a lyophilized powder, arrives at the lab. The vial gets a sample ID and is photographed for chain-of-custody records.
  2. Sample prep: The lab dissolves the peptide in a proper solvent, usually water, acetonitrile, or buffer, at a known concentration for analysis.
  3. HPLC analysis: The dissolved sample is injected into an HPLC system. The peptide separates on a reverse-phase C18 column, and a UV detector reads absorbance at 214 nm (peptide bond absorbance) and 280 nm (aromatic amino acids). The chromatogram shows peaks for each part, with retention times used for ID and peak areas used for purity.
  4. Mass spectrometry (LC-MS): If identity proof is needed, the sample is also run by mass spectrometry. The mass-to-charge ratio (m/z) is measured and compared with the claimed peptide's theoretical molecular weight. A match within a tight range, usually ±0.1%, confirms identity. It can also support peptide sequence analysis when you need a closer check on the expected mass.
  5. Fill weight measurement: The empty vial is weighed before and after the peptide is removed, and the difference gives the net fill weight. This shows how much material was really in the vial.
  6. Report generation: A Certificate of Analysis (COA) is made with all results: identity check, purity percentage, fill weight, and any extra tests done. The report includes chromatograms, mass spectra, and raw data.

What HPLC Tells You About Your Peptide

HPLC (High-Performance Liquid Chromatography) is the top method for peptide purity testing. When your sample runs through an HPLC system, the chromatogram shows several things:

  • Main peak: The biggest peak in the chromatogram is your target peptide. Its retention time, or how long it takes to leave the column, helps identify the compound.
  • Purity percentage: The area under the main peak divided by the total area of all peaks gives the purity percentage. A research-grade peptide should be ≥98% pure.
  • Impurities: Smaller peaks beside the main peak are impurities. These may be short sequences, deleted peptides, leftover protecting groups from synthesis, or breakdown products.
  • Retention time consistency: Compare your sample's retention time with a reference standard of the same peptide. That confirms identity at the HPLC level.

What Mass Spectrometry (LC-MS) Adds

While HPLC tells you how pure your sample is, mass spectrometry tells you what the peptide is. LC-MS measures the peptide's mass with high precision. If the measured mass matches the mass your vendor claimed to sell, identity is confirmed. If the mass is off, you may have the wrong peptide, a modified version, or a degraded product.

For example, if you ordered a peptide with a theoretical mass of 4,813.52 Da and the LC-MS shows 4,813.5 Da, identity is confirmed. But if the mass is 4,695 Da, you have a different compound, maybe a truncated or modified version.

FAQ: Peptide Testing

What is peptide testing?

Peptide testing is the lab analysis of a peptide sample to verify its identity, purity, and quantity. The most common methods are HPLC for purity and LC-MS for identity proof. This is a core part of peptide purity testing and peptide analysis.

How does HPLC peptide testing work?

HPLC splits the parts of a peptide sample by passing it through a column under high pressure. Each part leaves at a different retention time, which lets the lab check identity and purity by comparing the peptide peak area to impurities.

What is the difference between identity and purity testing?

Identity testing confirms that the peptide is what the label claims, using mass spectrometry to match the molecular weight. Purity testing measures how much of the sample is the target peptide versus contaminants, breakdown products, or leftover solvents.

How long does peptide testing take?

Standard HPLC peptide testing takes 5-7 business days from sample receipt. Extra tests like endotoxin screening, heavy metals analysis, or LC-MS confirmation may add 2-3 days.

How much peptide do I need to send for testing?

Most HPLC and LC-MS tests need only 0.5-1 mg of peptide. The test does not destroy the rest of the sample, which can be sent back if asked.

Is peptide testing confidential?

Yes. PepsReview's testing service is 100% confidential. Your sample data, results, and personal information are never shared with third parties. Results are sent only to the email address you provide.

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