HPLC vs LC-MS vs FTIR — Which Peptide Test Matters and Why
Four methods you'll see cited on peptide COAs: HPLC, LC-MS, FTIR, and CLND. Each answers a different question. This is what each test actually measures — and which ones matter for what you're trying to do.
Quick comparison
| Method | What it measures | What it misses |
|---|---|---|
| HPLC | Purity percentage (target peptide vs. chromatographic impurities) | Identity (similar compounds can co-elute); absolute peptide content |
| LC-MS | Identity (molecular mass confirmation) | Absolute content; secondary structure |
| FTIR | Secondary structure integrity (folding, aggregation) | Purity; identity (similar peptides can show similar spectra); content |
| CLND | Absolute peptide content (grams peptide per gram sample) | Identity; purity; structure |
HPLC — the minimum
High-Performance Liquid Chromatography is the industry baseline. Sample is pushed through a column; compounds elute at different times based on their interactions with the stationary phase. The chromatogram shows peaks; the target peptide has a characteristic retention time. Purity is reported as the percentage of the total peak area attributable to the target peak.
Strength: Precise, quantitative, reproducible. Industry-standard for ≥ 98% research-peptide purity claims.
Weakness:HPLC can't distinguish between the target peptide and a different compound with the same retention time. A deamidated impurity or a compound from incomplete deprotection could co-elute and be counted as target. LC-MS catches this.
LC-MS — identity confirmation
Liquid Chromatography – Mass Spectrometry adds a mass-spec detector downstream of the HPLC column. Each peak is ionised and its mass-to-charge (m/z) ratio measured. For a pentadecapeptide like BPC-157 (expected m/z ~ 1419), LC-MS will report the observed m/z and the expected m/z side by side.
Why it matters:if HPLC says "99% pure" and LC-MS says the observed mass is 1405 when 1419 was expected, you have a pure peptide — just not the one you ordered. HPLC alone can't catch this.
CLND — the one most vendors skip
Chemiluminescent Nitrogen Detector measures nitrogen content, which is nearly stoichiometric with peptide content. This gives you an absolute number: grams of peptide per gram of sample. HPLC tells you "of the compounds in your vial, 99% is the target peptide." CLND tells you "of the total mass in your vial, 72% is the target peptide — the rest is water, salts, and counter-ions."
The distinction matters most when you're dosing by weight in a research protocol. A 5 mg vial labelled as 99% pure peptide might deliver 3.6 mg of actual peptide if the CLND content is 72%. That's a 28% dosing error if you don't know to correct for it.
Currently in the EU segment, Particle Peptides is the only vendor reporting CLND as a standard parameter on every batch. That's the single biggest testing-transparency differentiator in the EU peptide market in 2026.
FTIR — structural integrity
Fourier-Transform Infrared Spectroscopy measures bond vibrations. The resulting IR spectrum is a fingerprint of the peptide's secondary structure. FTIR catches post-synthesis defects that HPLC and LC-MS can miss — aggregation, unwanted folding, oxidative modifications. Research Peptides Europe is currently the only EU vendor reporting FTIR as standard. FTIR alone is not sufficient — it's a complementary method that catches a narrow but important class of problems.
What a comprehensive COA actually uses
A comprehensivepeptide COA uses HPLC (purity) + LC-MS (identity) + CLND (content) + FTIR (structure) + LAL (endotoxin) + heavy metals screening + bioburden. That's the 7-parameter standard Particle Peptides publishes. Most EU vendors hit 2 or 3 of these (HPLC + LC-MS typically, sometimes LAL). The full set is the ceiling; the minimum that keeps a vendor credible is HPLC + LC-MS.
FAQ
Which testing method is most important?
HPLC is the non-negotiable minimum — it measures purity. LC-MS is the next step up because it confirms you actually have the peptide you expected, not a similar compound that elutes at the same retention time. FTIR and CLND add structural and content information respectively. In order of marginal value: HPLC (essential) → LC-MS (high) → CLND (meaningful for accurate dosing by weight) → FTIR (catches a narrow class of post-synthesis defects).
Why does CLND change the picture?
CLND measures actual peptide content in the vial — grams of peptide per gram of sample. HPLC purity is a ratio: what percentage of the chromatographic peaks is the target peptide. A vial can be 99% pure by HPLC (target peptide dominates the peaks) and only 70% peptide by CLND (residual water, salts, counter-ions making up the rest). If you dose by weight, CLND is the number that tells you how much peptide you're actually working with.
Can FTIR alone tell me a peptide is good?
No. FTIR confirms structural integrity but doesn't tell you purity or identity — a pure-but-wrong peptide can have a valid FTIR signature. FTIR is useful as one of several confirmatory methods, not as a standalone test.
What if my vendor only reports HPLC?
HPLC alone is acceptable for most research use cases, especially for well-characterised peptides from established vendors. The risk with HPLC-only: a contaminant that co-elutes with the target would be missed. LC-MS adds mass confirmation that catches that scenario. If the peptide is expensive or the experiment is dose-sensitive, the LC-MS upgrade is worth paying for.
Is an independent lab always better than in-house?
Independent is almost always stronger signal. Janoshik Analytical (Czech Republic) is the community-standard independent lab for research peptides. An in-house COA is not worthless — it's often the same analytical equipment run by trained staff — but the operator has an incentive to round up, and you as buyer have no way to verify that didn't happen. Independent reports remove the incentive conflict.