Glutathione

Sealed lyophilized vials are stored in the dark. The peptide-formulation literature regards the dry solid as the stable state and the solution as the fragile one: refrigeration at 2-8 degrees C is standard for short holding periods, and minus 20 degrees C or colder for long-term storage. Vials are brought to room temperature before opening so that atmospheric moisture does not condense onto the cold solid. Reduced glutathione oxidises readily on exposure to air and to trace metals; solutions are prepared fresh and the dry solid is kept sealed and cold.

For reconstitution, the diluent is added slowly down the inner wall of the vial rather than directly onto the cake, and the vial is swirled rather than shaken - agitation at an air-liquid interface is a well-documented driver of peptide aggregation. The solid should dissolve to a clear, particle-free solution; persistent cloudiness or visible particulate indicates the material should not be used.

Reconstituted solution is held at 2-8 degrees C and protected from light. Freeze-thaw cycling is the single most avoidable cause of loss, so where a solution must be frozen it is aliquoted first into single-use volumes. Working aliquots are labelled with the lot number so that any result can be traced back to the certificate of analysis for that lot.