It is important to avoid the loss of any product because of improper storage and distribution. The main purpose of low temperature storage is to avoid further biological activity i.e. genetic or enzymatic. At reduced temperatures processes are dramatically slowed down and come to a complete stop at -131°C which is called water transition temperature.
In other words, the storage temperature is based on the activity level of the sample and the expected storage period.
The following general guidlines are used in the medical/pharma industry:
- Short period storage within weeks can be done at -18 to -30°C using mechanical freezers.
- Medium period storage within 1-3 months can be done at -30 to -50°C using mechanical freezers.
- Long period storage within 6-12 months can be done at -50 to -80°C using ultra low mechanical freezers.
- Extended period storage (years) can be done at -131°C or lower using special cryogenic freezers or liquid nitrogen.
The process of freezing down and storing samples is done by using mechanical freezers or special storage tanks using LN2 (liquid nitrogen). This is typically used within the following medical/pharma applications:
- Stem cell storage
- Cord blood storage
- Cell line storage
- Other biological material storage
In the food industry, the FDA and HACCP regulate and control the specific requirements for storage of food products.
The critical parameter during storage is temperature but often humidity is also monitored.
Validation must be conducted regularly to ensure that a low temperature cabinet or cryogenic freezer is capable of accurate and repeatable performance. Ellab has a variety of wireless loggers that are capable of monitoring down to -80°C. The battery management system and design of the data logger and flexible sensors makes them highly suitable for cold storage applications.
Cold storage systems vary in design based on storage volume and temperature range. The only parameters of interest are temperature and humidity. Samples are often placed in closed containers so no cross contamination is possible.
Validation of cold storage freezers/tanks generally falls into three main categories.
Standard laboratory freezers/cabinets with temperature range of -10 to -30°C do not usually pose any special challenges because parameters to be controlled are relatively easy to match. As temperatures are modest and no pressure measurements are needed, the measurement range of the Lab logger can be used and to simplify the operation the LED indicator will provide the operator with instant information regarding the logger status.
Low temperature freezers that operate between -30 to -80°C require special equipment due to the low temperatures. Ellab has a variety of low temperature loggers that are ideal for this temperature range (Pro X, Frigo, Compact Ultra X, Pro XL).
Ultra-Low temperature freezers (or Cryogenics) as well as LN2 tanks require special equipment as temperature exposure will make most materials very fragile thus breakage by mechanical stress can happen. When using cable based equipment the E-Val™ Pro special metal sheeted SSU-MM probes are ideal. Ellab makes a variety of low temperature flexible sensors that can be used with our wireless loggers. It is recommended that the logger body is kept outside of these extreme conditions.
Wireless loggers fitted with the SKY option can process data in real-time, but for very small and low volume freezers/chambers that contain access port(s) using thermocouples could be advantageous to reduce impact on chamber volume.
Depending on the length of the validation process, the sample rate for data collection may need to be adjusted to match the logger memory capacity.
The FDA regards Mean Kinetic Temperature (MKT) as a calculation that will show if a product has exceeded storage conditions. MKT can also be used to determine if storage, handling, shipment, etc. has affected the shelf life of the product.MKT is a calculated fixed temperature that replicates the effects of temperature variations on a product over a period of time.. It expresses the cumulative thermal stress experienced by a product at varying temperatures during storage. In addition to MKT it is recommended that min and max values are calculated including a description of the time and placeof occurrence.
Potential challenges when validating a cold storage system are:
- To determine the cold and warm zones of the cold storage system
- To confirm pre-defined temperature / humidity ranges
- To identify and improve temperature / humidity equilibration
- To determine the highest temperature / humidity fluctuations within the cold storage chamber
- To calculate and document the Mean Kinetic Temperature
There are no specific standards covering cold storage validation but Ellab’s ValSuite™ Pro software calculates MKT according to these standards:
- USP chapter no. 1151:”Pharmaceutical Dosage Forms in chapter Stability”.
- ICH norm no. Q1A (R2) page 15.
Validation of a cold storage system consists of various steps regarding Installation Qualification (IQ), Operational Qualifications (OQ) and Performance Qualifications (PQ).
The IQ is conducted to demonstrate that the cold storage system is inspected and contains all the required parts for its proper functioning.
In the OQ, the performance of the cold storage system and its operational procedure is verified. The OQ portion consists of temperature mapping of the empty chamber over several hours to confirm that the empty chamber works within the specified limits throughout the chamber. The OQ also contains information about the calibration of the measuring equipment and defines the location of the thermocouples and /or data loggers in the chamber. Finally, checking of the warning and alarm limits adds to the test.
The PQ verifies that the loaded cold storage chamber is capable of reaching and maintaining the target temperature range and works (while loaded) within the specified limits of temperature. The specified limits of temperature throughout the chamber are typically measured for up to 30 days to verify that the environment is stable over time.
The effect of opening doors for two different lengths of time and the effect of a power failure on the cold storage is also tested.
Ambient temperature during test shall be 22 +/-3°C.
A specified number of loggers are placed in the cold storage system in the pre-determined critical mapping points while taking into account the expected gradient throughout the chamber. The temperature mapping is typically performed over a minimum period of 48 hours.
Generally, the temperature mapping grid should have all temperature recording devices and loggers positioned at distances following the sensor’s capacity to efficiently measure the temperature changes across the entire volume. The mapping grid should allow the thermal mapping activity to capture both the hot and the cold zones.
The frequency of the temperature mapping is done at least once a year. Additional temperature mapping may be required for changes such as conditions mentioned below:
- Temperature settings change
- Changes made to the storage capacity
- Replacement of critical components e.g. valves or compressors
- New accessory is installed that may impact the temperature and relative humidity
- Any other changes made that could affect temperature/humidity
For pharmaceutical clients, most applications will require the use of advanced software such as ValSuite™ Pro with its 21 CFR Part 11 compliance and sophisticated reports/features. For validation purposes creating a Unit with the exact position of each measuring point is advantageous when handling many sample points. Further, adding it all up in a Profile including a Limit Report as well as Statistical Report is useful and time saving.
At the end of each study report(s) can be signed by Electronic Signature(s), stored, printed, and distributed in a secure and locked PDF format. For other clients that do not need the electronic records, ValSuite Basic is the right choice. This software version provides the same Statistical and Limit report options but without the Part 11 compliance.
Using the built-in calibration functionality, users can calibrate the Ellab sensors at regular intervals. The ValSuite™ Pro software generates an easy to read calibration report that includes all measurements and tolerances that are defined by the user. It is recommended that Ellab sensors and probes are sent in at least once a year for factory calibration (which includes a traceable calibration certificate).