Moisture Control in Laboratory Storage

Lyophilised research peptides are supplied as dry powders, and keeping them dry is central to maintaining their condition in storage. Moisture, meaning water present as absorbed liquid or as humidity in the surrounding air, can drive chemical reactions including hydrolysis and deamidation. Even small amounts of absorbed water can accelerate these reactions over time, particularly when material is stored for extended periods. The overview below describes moisture management in general laboratory storage terms; it contains no instructions for any use of a material.

Relative humidity (RH) is the amount of water vapour in air expressed as a percentage of the maximum amount the air can hold at a given temperature. A material stored in a humid environment will absorb moisture from the air until it reaches equilibrium with the surrounding humidity. The amount of water a dry material absorbs at a given relative humidity is its equilibrium moisture content, which varies between materials depending on their chemical composition and physical form.

Reducing the relative humidity of the storage environment reduces the amount of moisture available for absorption. Cold storage contributes to this indirectly: cold air holds less water vapour than warm air at the same relative humidity, so a sealed cold storage unit with low initial humidity maintains a drier atmosphere than ambient storage in a typical laboratory.

What desiccants do

A desiccant is a material that absorbs moisture from the surrounding air, reducing the local humidity within a sealed container. Desiccants are commonly used in the packaging of dry research materials and in the storage containers or boxes used to hold vials in the laboratory. By absorbing moisture from the air inside a sealed container, a desiccant helps maintain a low-humidity environment around the stored material.

Common desiccant types

Silica gel is the most widely encountered desiccant in laboratory and pharmaceutical packaging. It is available in indicating forms that change colour when saturated with moisture, providing a visual indicator of desiccant condition. Molecular sieves, which are porous materials with precisely controlled pore sizes, are used where very low humidity levels must be maintained. Calcium sulfate and calcium chloride are also used in various applications. Desiccants have a finite capacity and must be replaced or regenerated once saturated.

A common source of unintended moisture exposure is condensation that forms on a cold vial when it is removed from frozen storage into warmer, more humid laboratory air. Water vapour from the air condenses on the cold surface of the vial, and if the vial is opened before it has warmed to room temperature, this condensed water can come into contact with the dry material inside.

The standard practice to avoid this is straightforward: allow the sealed vial to equilibrate to room temperature before opening. The equilibration time needed depends on the temperature difference and the volume of the vial, but allowing a vial to stand sealed for several minutes at room temperature before opening is generally sufficient to prevent condensation from forming on the material inside. This is discussed as a common avoidable storage issue in Common Laboratory Storage Mistakes.

Keeping vials sealed until use is the most direct form of moisture control available during laboratory handling. A sealed vial does not exchange moisture with the surrounding atmosphere. Once a vial is opened, the material inside is in equilibrium with the ambient humidity for the duration of the handling, so minimising the time material is exposed to open air and resealing promptly are both important practices.

For research materials stored in secondary containers such as boxes or bags alongside desiccant, keeping those containers sealed until material is needed extends the benefit of the desiccant to the entire storage batch. For the broader context of how research materials are packaged for supply, see How Research Materials Are Packaged.

The lyophilised format of most research peptides is itself a form of moisture control at the manufacturing stage. Freeze drying removes water from the material by sublimation, leaving behind a dry solid with very low residual moisture content. The resulting powder is then sealed into a vial, which protects it from reabsorbing moisture. Understanding the process behind the format helps explain why the sealed vial is effective at maintaining dryness, and why storage practices focus on preserving the seal and the dry atmosphere inside it. For a description of the freeze drying process itself, see Understanding the Freeze Drying Process. General storage guidance is given in Peptide Storage Guidelines.