Ultra-low temperature (ULT) freezers are essential pieces of lab equipment used to store samples at or below -80oC. They are available in a range of formats, including upright or chest freezer configurations to suit different laboratory footprint requirements, and incorporate a multitude of design features to ensure they perform consistently over an extended period of time. These comprise high-efficiency refrigerants, frost reduction mechanisms, alarm systems, pressure equalization ports, and many more besides, but there is also an onus on researchers to take responsibility for prolonging ULT freezer life.
Any sample deemed worthy of storage in a ULT freezer is precious. However, genomic material can especially benefit from the long-term protection that ULT freezers provide. Not only are genomic samples highly susceptible to chemical and enzymatic degradation when stored at -20oC, but they are also readily compromised by repeated freeze-thaw cycles that are an inherent risk of shared -20oC freezers being continually opened and closed - a risk that is heightened when the low volume aliquots so often used for genomic research are positioned near to the freezer door.
By storing genomic samples in a ULT freezer benefiting from measures having been put in place to increase freezer efficiency, researchers can be confident that materials are kept safe. Here, we suggest some simple yet effective ways to enhance the performance of your ULT freezer, so that it will provide you with many years of reliable service and assure you of results you can trust whatever type of sample material you’re working with.
Position Your ULT Freezer Wisely
Introducing a ULT freezer into the lab involves more than simply plugging it in, cooling it down, and filling it with samples. Ideally, the lab should have an ambient temperature no higher than 32oC, with conditions being tightly regulated to avoid fluctuations that can force the ULT freezer to work harder. It is also important that the ULT freezer is not positioned close to other laboratory equipment capable of generating heat (e.g. autoclaves, CO2 incubators, ultracentrifuges), and that it is not exposed to direct sunlight or drafts (e.g. from heating or cooling vents). Ensuring there are several inches of space between the ULT freezer and the wall is essential to maintain effective air circulation, and the freezer should always be leveled prior to use; this is typically achieved using adjustable feet.
Perform Regular Preventative Maintenance
Regular preventative maintenance is critical to keep your ULT freezer running efficiently. This includes periodic removal of frost or ice build-up from the inner chamber using a scraping device, and from the inner and outer door gaskets by wiping them with a soft cloth. During the maintenance process, it is vital that the condenser is not overlooked. The condenser plays a central role in ULT storage by transferring heat from inside the ULT freezer to the lab, but it can only function optimally if the filter and coil are cleaned regularly to avoid a build-up of dust. Other routine preventative maintenance measures should include clearing the vacuum relief port to prevent it from becoming blocked; habitually inspecting the ULT freezer for any signs of wear and tear, and fully defrosting the chamber at least twice a year depending on usage and environmental conditions.
Pay Attention to Alarms and Warning Lights
Most ULT freezers are fitted with one or more alarms to rapidly alert researchers to sub-optimal operating conditions. These might be high temperature, power failure, low battery life, prolonged door opening, or malfunction of the freezer monitoring system, any of which could compromise the integrity of the sample material within. While it is imperative that alarms are not ignored, addressing the issues they are designed to highlight requires knowing what the different alarms actually mean and having a plan of action in place for situations where operator intervention is required. A tried and trusted approach involves labeling each freezer clearly with a key to the different alarm codes, alongside up-to-date details of a point of contact and a deputy. It is also sensible to have spare ULT freezer space available should it become necessary to transfer samples to an alternative unit.
Ensure Your ULT freezer is Connected to a Back-Up Power Supply
Nothing prevents a ULT freezer from performing efficiently – or indeed performing at all – quite like a power outage. However, the very nature of the material that is stored at ultralow temperatures dictates that ULT freezers will invariably be connected to some form of back-up power supply or generator. Even where this is not the case, freezer alarms will usually still function during a power outage since the display and buzzer are typically powered by a battery; checking the battery lifetime during routine cleaning and maintenance is good practice to eliminate the risk of sub-optimal operating conditions going unnoticed (e.g. if a power outage occurs when no one is around). Should there be a delay between the power going out and the back-up generator kicking in, it is essential that the door to the ULT freezer remains closed.
Implement Smart Working Practices
Good working practices go a long way toward ensuring your ULT freezer performs efficiently. These include opening the door to the freezer as infrequently as possible and keeping the length of time the door is held open to a minimum. It is also sensible to make sure samples are cold before transferring them to the ULT freezer for storage since this will prevent other material in the vicinity from warming up and will also help reduce the build-up of condensation that can damage door gaskets. Further measures involve keeping the ULT freezer relatively full so that ultra-low temperatures are more easily maintained, and positioning samples sensibly so that they are accessible. Many researchers choose to fit their ULT freezer with a racking system and to keep a current record – either an electronic file with shared access or a paper document placed next to the ULT freezer – indicating where various samples can be found. This streamlines the process of moving material in and out and can also be useful when the time comes to rationalize which samples should remain in storage.
About the Author:
Emma Easthope is a contributor at Cambridge Technical Contect Ltd.