Reading
a certificate of analysis

A certificate of analysis (CoA) records the results of tests run on one specific lot. It is only meaningful for that lot: a certificate for a different lot number, however good, tells you nothing about the vial in your hand.

Product and sequence

The compound the lab believed it was testing, written out in full.

Lot number

The link between the document and the vial. It should match your label exactly.

Theoretical (calculated) mass

Computed from the sequence and its modifications. Our product pages show both the average and the monoisotopic figure.

Observed mass

What mass spectrometry actually measured. This is the identity test.

Purity

Usually reversed-phase HPLC with UV detection at about 214–220 nm, reported as a percentage of total peak area.

Test date and laboratory

When and where the analysis was done.

1. The lot number matches the vial.

2. The observed mass agrees with the theoretical mass, within the stated tolerance.

   Compare like with like: average with average, monoisotopic with monoisotopic. A typical tolerance is about 1 Da for an average mass, or about 10 ppm from a high-resolution instrument. Electrospray instruments often report several charge states, such as [M+2H]²⁺ and [M+3H]³⁺; the deconvoluted mass is the one to compare.

3. The purity method is stated: column type, wavelength or both.

   A bare number without a method is weaker evidence.

4. The date is plausible for the lot, and the document names who did the testing.

HPLC purity and MS identity say nothing about sterility, endotoxin or how much of the powder’s weight is peptide (water and counter-ions such as acetate or trifluoroacetate also weigh something). If a certificate reports those tests, they appear as separate lines.