Lyophilized peptides want three things: low temperature, low humidity, and darkness. A frost-free freezer that cycles is worse than a stable −20 °C chest. Desiccant in the vial or bag is not optional if the cake will be opened more than once.
Once water is back in the vial, hydrolysis starts. Refrigerate reconstituted stocks at 2–8 °C. Do not freeze–thaw as a habit; ice crystals and pH micro-shifts chew sequences. If you need months of working solution, aliquot.
What ‘purity’ means
HPLC purity is the area of the main peak versus other UV-active species. It is not identity. A 99% peak can still be the wrong peptide if the sequence was never confirmed by mass spectrometry. Vought lists HPLC because that is what catalogs list; MS and amino-acid analysis are how you actually know.
Acetate and TFA are counter-ions, not contaminants in the moral sense, but TFA can irritate cells. Research that cares about cell assays often exchanges TFA for acetate.