You’ve requested a Certificate of Analysis for your peptide order — now what? Here’s a practical guide to understanding what the numbers actually mean.
The two key tests
Most peptide purity reports include results from two primary analytical methods: HPLC and mass spectrometry. Together, they answer two fundamental questions:
- Is this the right peptide? (identity)
- How pure is it? (purity)
HPLC: Measuring purity
What it is
High-Performance Liquid Chromatography (HPLC) is a technique that separates the components of a sample based on their chemical properties. The peptide solution is pushed through a column under high pressure, and different molecules pass through at different speeds.
How to read the results
The output is a chromatogram — a graph showing peaks at different retention times. Here’s what to look for:
Main peak: This represents your target peptide. Its area relative to the total area of all peaks gives you the purity percentage.
- 98%+ purity — research grade, suitable for reliable studies
- 95-98% — acceptable for some applications but may contain interfering impurities
- Below 95% — not recommended for research where accuracy matters
Secondary peaks: These represent impurities — incomplete synthesis products, degradation products, or contaminants. Smaller and fewer secondary peaks indicate a cleaner product.
Retention time: The time at which the main peak appears. This should be consistent with the expected value for that specific peptide.
What affects HPLC results
- Column type and conditions — different columns can give slightly different results
- Solvent gradient — the rate at which the mobile phase changes
- Detection wavelength — typically 214nm or 220nm for peptides
Mass spectrometry: Confirming identity
What it is
Mass spectrometry (MS) measures the molecular weight of compounds in a sample. For peptides, it confirms that the molecule has the correct mass — and therefore the correct amino acid sequence.
How to read the results
Observed mass vs theoretical mass: The report will show:
- Theoretical mass — the calculated molecular weight based on the peptide’s amino acid sequence
- Observed mass — the mass measured by the instrument
These should match within the instrument’s tolerance (typically within 0.1-0.5 Da for modern instruments).
What a mismatch means:
- A significantly different mass suggests the wrong peptide or a synthesis error
- A slightly higher mass might indicate adducts (additional molecules attached)
- A slightly lower mass might indicate truncation (missing amino acids)
Common mass spectrometry methods
- ESI-MS (Electrospray Ionisation) — most common for peptides
- MALDI-TOF — useful for larger peptides and proteins
- LC-MS — combines HPLC separation with mass spectrometry detection
Other tests you might see
Amino acid analysis
Breaks the peptide down into individual amino acids and quantifies each one. Confirms the correct ratio of amino acids is present.
Endotoxin testing
Measures bacterial endotoxin levels. Important for peptides used in sensitive research applications.
Solubility test
Confirms the peptide dissolves properly in the recommended solvent at the expected concentration.
Appearance
Visual description of the lyophilised product — typically “white to off-white powder.”
Putting it all together
A good purity report should give you confidence in three things:
| Question | Test | What to look for |
|---|---|---|
| Is this the right peptide? | Mass spectrometry | Observed mass matches theoretical mass |
| How pure is it? | HPLC | 98%+ main peak area |
| Is the batch traceable? | Lot/batch number | Unique identifier matching your product |
What Eterna Labs provides
Every batch of Eterna Labs peptides is independently tested via HPLC and mass spectrometry. COAs are available on request — just email us with your order number.
We believe if a supplier can’t show you the data, you shouldn’t trust the product.
Eterna Labs supplies third-party tested, research-grade peptides across New Zealand. Browse our range at eternlabs.co.nz/shop.
Research compounds mentioned
- BPC-157— used as a purity report example throughout this article
- Retatrutide— one of the compounds referenced for HPLC purity benchmarking
- GHK-Cu— a flagship peptide whose purity documentation is publicly available