Two analytical methods dominate research peptide quality control: high-performance liquid chromatography (HPLC) and mass spectrometry (MS). They are often mentioned together, sometimes interchangeably — but they answer two completely different questions. A supplier quoting only one of them has told you half the story.
The two questions every lot must answer
- Is it the right molecule? → identity → mass spectrometry
- How much of the vial is that molecule? → purity → HPLC
How HPLC purity works
In reversed-phase HPLC, the dissolved sample is pushed through a column that separates molecules by hydrophobicity. Each component exits (“elutes”) at a characteristic retention time and is measured by UV absorbance, typically at 214–220 nm where peptide bonds absorb. The result is a chromatogram — a series of peaks.
Purity is the target peak’s percentage of total peak area. A ≥99% purity result means the impurities visible to the method — truncated sequences from synthesis, deletion products, oxidized variants — together account for less than 1% of the signal.
What HPLC cannot tell you: that the main peak is actually your peptide. A completely wrong compound can produce one beautiful, sharp, 99.9% peak. Purity without identity is a percentage of an unknown.
How mass spectrometry identity works
Mass spectrometry ionizes the peptide and measures its mass-to-charge ratio with high precision. The observed mass is compared to the theoretical mass calculated from the amino-acid sequence. Agreement within the instrument’s tolerance confirms the molecular composition; disagreement means the wrong sequence, a major modification, or a different compound entirely.
Two instruments are common in peptide QC: ESI-MS (electrospray ionization, often coupled directly to an LC system as LC-MS) and MALDI-TOF (matrix-assisted laser desorption, time-of-flight). Either is acceptable — what matters is that the COA states the observed mass next to the theoretical one.
What MS cannot tell you: how much of the vial is that molecule. A correct identity result can coexist with poor purity.
Why both, always
Only the pair closes the loop: MS proves the molecule, HPLC proves the proportion. That is why every Heartland Bio Labs research compound is released with both results on its certificate — ≥99% HPLC purity and mass-spec identity — published lot-by-lot in the public COA portal.
Reading the results like a reviewer
- Find the theoretical mass and the observed mass — they should agree closely.
- Check the purity method: HPLC with stated detection wavelength beats an unlabeled “purity” number.
- Match the lot number on the certificate to the vial.
- Prefer suppliers that publish certificates publicly rather than on request. (Here is how to read a full COA, section by section.)
All compounds discussed are for in vitro laboratory research use only — not for human or veterinary use.