Storing cryovials in liquid nitrogen is a reliable way to preserve biological samples for long periods. Liquid nitrogen provides ultra-low temperatures of -196°C (-321°F), which stop biological processes and keep samples like cells, tissues, and DNA intact. However, proper storage techniques are essential to maintain sample quality and ensure safety while handling liquid nitrogen.
Understand Liquid Nitrogen Storage
Liquid nitrogen has a temperature of -196°C (-321°F), ideal for halting biological activity and preserving cells, tissues, and other samples. It is used in two main types of storage systems: liquid phase and vapor phase. In liquid phase storage, cryovials are fully submerged in liquid nitrogen, providing consistent ultra-low temperatures. In vapor phase storage, the vials are stored above the liquid surface in nitrogen vapor. Vapor phase storage is generally considered safer as it minimizes the risk of contamination and prevents liquid nitrogen from entering the vials, which could cause them to burst when warmed.
Select the Right Cryovials
High-quality cryovials designed for cryogenic temperatures are essential. Look for:
- Leak-proof caps to prevent nitrogen entry.
- Sterile, durable materials resistant to cracking at low temperatures.
- Internal or external threading based on your storage preference. Ensure the vials are compatible with your storage system (liquid or vapor phase).
Prepare Samples for Storage
Proper preparation is essential to keep samples safe in cryovials. Make sure to label each vial clearly with a permanent marker or cryo labels that won’t fade or peel in freezing temperatures. When filling the vials, leave a small air gap to allow for any expansion during freezing. These simple steps help protect the samples and prevent problems during storage.
Safety Precautions
Working with liquid nitrogen involves risks:
- Wear cryogenic gloves and a face shield to prevent burns.
- Use lab coats and closed-toe shoes.
- Always work in a well-ventilated area to avoid nitrogen gas buildup, which can displace oxygen and pose a suffocation risk.
Use Cryogenic Storage Racks
Organize your cryovials using cryogenic racks or boxes specifically designed for liquid nitrogen storage. These racks help maximize storage efficiency by allowing you to store more vials in a limited space. They also make it easy to retrieve specific samples quickly, saving you time when you need to access your materials. Additionally, using cryogenic racks reduces the amount of time the vials spend outside the storage environment, which helps maintain the necessary low temperatures and ensures your samples remain properly preserved.
Storing Cryovials in the Liquid Phase
For liquid phase storage:
- Submerge the cryovials in liquid nitrogen using a rack.
- Ensure the caps are tightly sealed to prevent liquid nitrogen from entering the vials.
- Avoid frequent handling to minimize contamination risk.
Storing Cryovials in the Vapor Phase
For vapor phase storage:
- Place the cryovials in a designated rack above the liquid nitrogen surface.
- Ensure the level of liquid nitrogen is sufficient to maintain a stable vapor environment.
- Periodically check the nitrogen level to avoid temperature fluctuations.
Handling and Retrieval
To minimize temperature fluctuations during handling, use specialized cryogenic tools to retrieve vials quickly and efficiently. Avoid keeping the storage container open for long periods, as this can cause the temperature to rise and compromise the samples. Maintaining a detailed log of stored samples is also essential for quick identification and tracking, reducing the need to search through the storage system unnecessarily.
Key Considerations for Long-Term Storage
- Regularly review and update inventory records.
- Avoid overfilling vials, as this may lead to breakage.
- Train lab personnel on proper handling and safety protocols.
Storing cryovials in liquid nitrogen may seem complex, but following these steps makes the process manageable and safe. Selecting the right cryovials, labeling them clearly, and organizing them in cryogenic racks ensure your samples are easy to store and retrieve. With proper preparation and regular maintenance of the storage system, you can preserve your samples for years without compromising their quality.
By understanding the best practices and safety measures, you can make the most of liquid nitrogen storage and protect your valuable research samples.