Research Education

How to Read a Peptide Certificate of Analysis: HPLC and Mass Spectrometry Explained

Aūra Research · laboratory reference

A research peptide arrives as white lyophilised powder. The Certificate of Analysis is the only document that says what the powder is. Read properly, it answers two questions: identity and purity.

Almost every peptide COA rests on two techniques, high-performance liquid chromatography and mass spectrometry. One measures how much. The other confirms what.

What a Certificate of Analysis records

A usable peptide COA carries the product name and amino acid sequence, a batch or lot number, HPLC purity as a percentage, molecular weight by mass spectrometry, appearance, net peptide content and the test date with the responsible laboratory. Strong documents attach the raw instrument output too: the chromatogram behind the purity figure and the spectrum behind the mass.

The scope is narrow by design. A COA describes the dry powder as tested. It says nothing about what happens once that powder is dissolved, which depends on storage and on the diluent chosen at reconstitution.

How HPLC purity is calculated

HPLC pumps a sample under pressure through a packed column. Molecules cross at different speeds and leave at different times, so a detector records them separately.

Peptide work uses reversed-phase HPLC almost exclusively. The packing is non-polar, usually silica bonded with C18 chains, and the mobile phase is polar. More hydrophobic molecules hold on longer, then release as the organic proportion rises through the gradient. The mode resolved closely related sequences well, which made it the standard (Mant et al., 2007).

Two terms carry the result. Retention time is how long a component takes to cross the column under a fixed method; the main peak should land in the same place across batches. Peak area is the area under the detector trace, typically UV absorbance at 214 nm where the peptide bond itself absorbs. Purity comes from area, not height: the software integrates every peak and expresses the target as a percentage of the total.

That figure is relative. It ignores salts, water and anything that does not absorb at the detection wavelength, and quantitation without a pure reference sample carries its own error sources (Moffatt et al., 2000). Peaks can also hide inside one another, which is why peak purity assessment turns to two-dimensional chromatography coupled to mass spectrometry (Stoll et al., 2023).

What mass spectrometry confirms

Mass spectrometry measures mass-to-charge ratio. Two ionisation methods dominate peptide work. ESI sprays the sample from a charged capillary, produces multiply charged ions and couples directly to an HPLC system. MALDI-TOF co-crystallises the sample with a matrix, produces mostly singly charged ions and tolerates salts well. The two are complementary for molecular weight determination (Strupat, 2005).

A COA prints two masses. The theoretical value comes from the sequence; the observed value is what the instrument measured. Agreement within the stated tolerance confirms identity. Disagreement points to a wrong sequence, a deletion, incomplete deprotection or an unexpected modification, and the size of the gap is diagnostic, since synthesis impurities carry characteristic mass shifts (Lian et al., 2021).

Reading a COA line by line

1. Product name and sequence. The sequence should appear in one-letter or three-letter code with every modification listed. Modifications shift the theoretical mass, so this line must agree with the mass spectrometry line.
2. Batch or lot number. This is the only link between the paper and the physical vial. The number on the document should match the label.
3. Purity by HPLC. Look for the percentage plus column, gradient and detection wavelength. A bare figure with no method behind it cannot be reproduced.
4. Molecular weight. Compare theoretical against observed and note which ionisation technique produced the number.
5. Appearance and net peptide content. Net peptide content reports how much of the vial mass is peptide rather than counterion salt and residual water. It reads lower than HPLC purity, and the two are not interchangeable.
6. Test date and laboratory. A date and a named laboratory show the report was produced for the lot in hand, not copied from an earlier run.

Red flags on a peptide COA

Ask for the lot-matched COA before ordering, then check the number again on arrival. Aūra Research publishes third-party batch data across the best sellers range, including BPC-157.

All products sold by Aūra Research are strictly for laboratory research purposes only. They are not intended for human or animal consumption, medical, or therapeutic use.