Chemical Storage of Moisture-Sensitive Chemicals
Moisture-sensitive chemicals may oxidize, decompose or even evolve flammable gases when exposed to moisture or oxygen in the atmosphere. Therefore, proper storage and handling practices for moisture-sensitive chemicals play an important role in maintaining a safe laboratory environment.
Chemicals that absorb water vapor from the air (hygroscopic and deliquescent chemicals) are not easy to store. If they are not stored properly, massing a small amount can be a challenge. For example, ammonium chloride, a commonly used inorganic salt, is a hygroscopic chemical with a fair to poor shelf life. Over time, it can change from free-flowing crystals to a rigid mass that is nearly impossible to remove from the bottle. A deliquescent chemical such as iron(II) chloride can absorb a large amount of water vapor from the air, to the point that it dissolves in the absorbed water turning into a solution.
Here are some ideas and tips to help you safely store and protect your moisture-sensitive chemicals. Some suggestions are simple and economical while others are sophisticated and more costly. Pick the techniques that meet your needs and budget.
Simple Tips
- Wrap Parafilm® around the cap of the chemical bottle. The Parafilm® will adhere tightly to the cap/bottle and minimize the amount of moisture that enters the bottle.
- A simple plastic poly bag, twist tie and desiccant packet can help preserve moisture-sensitive chemicals. Place the bottle in a bag, add a desiccant packet inside the bag and twist tie closed.
- Use a new, clean paint can and kitty litter to provide another layer of protection. Place the chemical bottle in a poly bag, add a shallow layer of kitty litter on the bottom of the can, put the bagged bottle in the can and fill the can with kitty litter. Then place the lid on the can.
- Order only the chemicals needed for a semester or one school year. Upon receipt, add the chemicals to your inventory list or program and label the chemical containers with the date of purchase.
Sophisticated Equipment Options
Desiccators provide a more advanced method of safely storing moisture-sensitive chemicals. Many varieties and sizes are available. They are typically made of plastic or glass, and some desiccators have valves for vacuum pump evacuation, which can remove moisture from the desiccator. Simply add desiccant (sold separately) to the compartment, add the chemical bottles and place the lid on the desiccator. Your best choice for a desiccant is anhydrous calcium sulfate or calcium chloride. Sometimes these are available in two forms: indicating and non-indicating. Indicating means the desiccant will change color when fully saturated and replacement is needed.
Glove Boxes offer highly specialized chambers for effectively storing and handling moisture-sensitive chemicals. In fact, some research labs keep their most dangerous chemicals such as potassium or sodium metals in glove boxes. Gas ports allow the creation of a high purity atmosphere using an inert gas such as argon or nitrogen. The user inserts chemicals, weighing materials, etc. via a portal that is evacuated of any ambient air. Once evacuation is done, the chemical is only exposed to a moisture- and oxygen-free atmosphere, which allows for prolonged, safe chemical storage.
I hope this information helps you conveniently and safely store your moisture-sensitive chemicals so they are ready to use when you need them.
Sincerely,
Joan Berry
Senior Chemist