1. HPLC purity: how clean, not what it is
High-performance liquid chromatography separates the sample into its components and reports the target peak as a percentage of total detected peak area. A figure of 99.1% means the main peak accounts for 99.1% of what the detector saw — usually at 214 or 220 nm, which is where the peptide bond absorbs. Anything below roughly 98% introduces related impurities that you cannot correct for downstream in an assay.
Look for the actual chromatogram, not just a number: retention time, a labelled main peak, and visible baseline. A stated percentage without a trace is an assertion, not a measurement.
2. Mass spectrometry: identity confirmation
MS compares the measured molecular mass against the theoretical mass calculated from the sequence. A match within the instrument's tolerance confirms you have the right molecule. HPLC alone cannot do this — a very pure sample of the wrong compound still reads as pure.
3. Net peptide content
Lyophilised material also contains counter-ions (commonly acetate or trifluoroacetate) and residual water. Net peptide content states how much of the vial mass is actually peptide, typically 75–90%. If your calculations depend on exact mass, this line matters more than the purity percentage.
4. What a genuine report must contain
- Compound name, in-house code and the batch or lot number of your vial
- HPLC chromatogram with calculated purity and method conditions
- Mass spectrum with measured versus theoretical mass
- Net peptide content, appearance and the analysis date
- The name of the laboratory that performed the analysis
Every batch we ship has its report published openly on the lab results page, so you can check the paperwork before ordering rather than after.
5. Red flags
- No batch number, or a batch number that does not match the vial label
- The same chromatogram image reused across different products
- No analysis date, or a date years older than the batch
- No testing laboratory named anywhere in the document
- Purity quoted as ">99%" with nothing behind it
Frequently asked questions
What does HPLC purity measure?
The share of total detected peak area belonging to the target compound.
Why is MS needed too?
Because purity says nothing about identity; MS confirms the molecular mass.
What is net peptide content?
The proportion of the vial mass that is peptide rather than salts and water.
Further reading
See our storage and handling guide, the European buying guide, and what are peptides for the basics. All material is supplied for laboratory research only — see the RUO disclaimer.