Peptides usually are provided as lyophilizates, which tend to be hygroscopic. Adsorption of humidity will reduce the peptide content and adhered water may decrease stability. Before opening, the vial should be allowed to reach ambient temperature in a desiccator. Lyophilizates often “stick” due to electrostatic charging. The peptide has to be weighed out quickly and the vial resealed.
Except for handling very short peptides or large amounts, reconstituting the peptide and aliquoting the resulting solution is preferable to weighing out.