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Is underfilling common in research peptides?
The short answer
Quantity against label claim is the most frequently reported failure mode in public peptide testing datasets — more common than wrong identity. Much of it appears to be systematic rather than deliberate: filling by powder weight without correcting for counter-ion and moisture produces consistent under-delivery even from suppliers acting in good faith.
In detail
The distinction between systematic and deliberate is useful because the remedy differs. A supplier correcting for net peptide content fixes it permanently; a supplier who cannot explain their filling basis probably has not thought about it.
It also explains why identity-only testing gives false comfort. Confirming that a vial contains the right peptide says nothing about how much.
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