When a research peptide is described as 99 percent pure, that number comes from HPLC. This explains what the test measures, what the number does and does not tell you, and why it has to be run per batch.
What HPLC does
High-performance liquid chromatography pushes a dissolved sample through a column that separates its components by how strongly each one interacts with the column material. Each component leaves the column at a different time and registers as a peak. The purity percentage is the area of the target peptide peak as a fraction of the total peak area. A 99 percent result means the target sequence accounts for 99 percent of what the detector saw.
What the other one percent is
The remainder is impurities from synthesis: truncated sequences that are missing residues, deletion sequences, and residual reagents or salts. These matter for research because they introduce variables. If a batch carries a different impurity profile, results that depend on the peptide can shift for reasons that have nothing to do with the experiment.
Purity is not identity
HPLC answers how much. It does not by itself confirm that the main peak is the correct molecule. That is the job of mass spectrometry, which measures molecular weight and confirms identity. A complete analytical picture uses both: HPLC for purity, MS for identity. A purity figure with no identity confirmation is incomplete.
Why it has to be per batch
Each synthesis run is its own batch with its own impurity profile. A purity figure from an old batch does not describe the batch in your hand. This is why testing has to be lot-specific and why the COA has to match the exact lot you received.
What a purity number does not cover
HPLC purity says nothing about sterility or endotoxin load. Those are separate tests. A high purity result is a statement about composition, not about anything else.
SynproLabs tests every batch by third-party HPLC and reports it on a lot-specific COA. That is the standard the number is only meaningful against.
For laboratory research use only. Not for human consumption.