What a high purity percentage can support

A high purity percentage can support one useful conclusion: under the stated analytical conditions, the main detectable peptide-related component represented most of the measured response. That makes the number valuable for lot screening, purification assessment, and estimating whether related byproducts are likely to interfere with a sensitive laboratory workflow. In research settings, this is meaningful because peptide-related impurities are not just paperwork problems. They can alter assay interpretation if they are present at meaningful levels or if they co-elute with the target compound. 

D’Hondt and co-authors review peptide impurities in detail and note that synthesis-related and degradation-related impurities can influence early functionality studies and even lead to erroneous conclusions. That review is one reason purity percentage remains a legitimate research buying metric. A cleaner chromatographic profile usually means fewer obvious related contaminants competing for interpretation. What it does not mean is that every other analytically relevant question has already been answered. 

Purity percentage can also support lot-to-lot comparison, but only when the same or demonstrably comparable method is used. If the method changes, the number may move partly because the chemistry moved and partly because the analytical window moved. For qualified laboratory buyers, comparability is strongest when the same method, reporting thresholds, detector, and documentation standard are used across lots.