How Research Peptides Are Tested: HPLC & Mass Spectrometry
Two analytical methods do most of the work in characterising a research peptide: reversed-phase HPLC for purity and mass spectrometry for identity. This guide explains what each one measures and why a credible batch needs both.
Reversed-phase HPLC — measuring purity
High-performance liquid chromatography separates the components of a sample as they travel through a column at different speeds. In reversed-phase HPLC (the common mode for peptides), the main peptide and its impurities elute at different times, producing a chromatogram of peaks. Purity is reported as the area of the main peak as a percentage of all peaks — so a single tall, clean peak indicates high purity, while extra peaks indicate impurities.
Mass spectrometry — confirming identity
A mass spectrometer ionises the molecule and measures its mass-to-charge ratio, giving a precise molecular mass. By comparing the detected mass with the expected mass for the target peptide, identity can be confirmed. This is the check that the right molecule was synthesised — HPLC alone cannot tell you that.
Why both are needed
Purity and identity answer different questions. HPLC tells you how much of the main component is present; MS tells you what that component is. A batch documented with HPLC purity AND LC-MS identity (expected vs detected mass) has been checked on both axes; one without the other is only half-characterised.
Independent vs in-house testing
Testing can be done in-house by the manufacturer or by an independent third-party analytical lab. Independent testing reduces the conflict of interest in a supplier certifying its own material. The certificate should state who performed the analysis and when.
How Index Peptides applies this
Each released batch is matched to a certificate of analysis recording RP-HPLC purity and LC-MS identity confirmation, published on the product page and verifiable by lot number on the verify page.
Frequently asked questions
What does RP-HPLC actually measure?
It separates a sample into its components and reports the main peptide's peak area as a percentage of the total — i.e. how pure the material is.
What does LC-MS confirm?
It measures the molecule's mass and compares it to the expected mass for the target compound, confirming the vial contains the right peptide.
Is third-party testing better than in-house?
Independent third-party testing removes the conflict of a supplier certifying its own material. Either way, the COA should name the testing party and date.
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