Introduction
Peptide purity is one of the most critical variables in research reproducibility. Impurities — whether residual synthesis reagents, truncated sequences, or oxidised variants — can confound experimental results and compromise data integrity. This guide should be read alongside our Peptide Storage & Stability guide and Peptide Reconstitution guide for a complete quality assurance workflow.
For research and laboratory use only. Not intended for human or veterinary use.
What Does Purity Percentage Mean?
Purity is expressed as the percentage of the target peptide relative to all UV-absorbing species detected in the analytical sample. A peptide stated as ≥98% pure contains no more than 2% combined impurities by this measure.
- ≥98% purity: Research grade — suitable for most in vitro and in vivo studies. All Vanta Labs peptides are supplied at ≥98% purity.
- ≥95% purity: Acceptable for many screening assays; less suitable for dose-response or mechanistic studies.
- <95% purity: Generally not appropriate for quantitative research applications.
Analytical Methods Used to Verify Purity
High-Performance Liquid Chromatography (HPLC)
- The gold standard for peptide purity analysis.
- Reverse-phase HPLC (RP-HPLC) separates peptide components by hydrophobicity.
- Results expressed as area-under-curve (AUC) percentage at 214 nm or 220 nm UV absorbance.
- A Certificate of Analysis (CoA) should include the HPLC chromatogram and stated purity value.
Mass Spectrometry (MS)
- Confirms molecular identity by verifying the molecular weight of the target peptide.
- Electrospray ionisation (ESI-MS) is most commonly used for research peptides.
- MS confirms correct sequence but does not quantify impurity levels — used in conjunction with HPLC, not as a standalone purity measure.
Common Impurity Types
- Truncated sequences: Incomplete synthesis products missing one or more amino acids.
- Deletion sequences: Peptides with internal amino acid omissions from failed coupling steps.
- Oxidised variants: Methionine- or tryptophan-containing peptides are susceptible to oxidation during synthesis or storage. GHK-Cu and AHK-Cu are particularly sensitive — see our Cosmetic & Skin Peptides overview for handling notes.
- Residual reagents: Synthesis solvents or protecting groups not fully removed during purification.
What to Look for in a Certificate of Analysis (CoA)
- Stated purity (%) with analytical method specified (e.g. RP-HPLC)
- Observed molecular weight vs theoretical molecular weight (MS confirmation)
- Batch/lot number for traceability
- Storage conditions and expiry/retest date
- Manufacturer or testing laboratory identification
Storage Impact on Purity
- Lyophilised peptides stored at −20°C in dry, dark conditions maintain purity for 24+ months in most cases.
- Repeated freeze-thaw cycles accelerate degradation — aliquot before freezing where possible.
- Reconstituted peptides degrade faster; use within recommended timeframes and re-verify purity if extended storage is required.
- Reconstitute with bacteriostatic water for multi-dose vials to extend reconstituted stability. Note: IGF peptides require acetic acid solution as primary solvent.
See our Peptide Dosing Protocols guide for guidance on concentration calculations and volume preparation.
All products supplied by Vanta Labs are intended strictly for laboratory and research purposes.