Laboratory Drying Agents

Classes of Drying Agents

Physically active agents adsorb water on the surface and in the pores of the matrices and can be regenerated by heating or applying a vacuum. Examples include: t.h.e.® Desiccant, silica gel, molecular sieve, aluminum oxide, etc. Chemically active agents have two possible modes of action.

Chemically Active Agents have two possible modes of action. Chemically active drying agents that bind the water in the form of crystallization may be regenerated by heating. These include calcium chloride, sodium sulfate, magnesium perchlorate, etc. Those chemically active drying agents that react with water cannot be regenerated. Examples of these include: Sicacide® and Sicapent®.

Types of Drying Agents

Indicating drying agents will change color in the presence of water. Exhaustion of such drying agents is easily detectable from the different color that develops upon saturation with water. After regeneration, an indicating drying agent will return to its original color and can be used again. For example, indicating silica gel contains minute quantities of an indicator which is orange in the anhydrous state. Exhaustion of the gel is easily detectable from the pink color that develops upon saturation with water. After being heated at 150-250°C in a drying oven, the silica gel will revert to its original orange color and can be re-used.