Credit: Andy Tay
Recently, my colleagues and I faced a huge dilemma during our lab clean-up. “Reagent A is expired. Should we toss it away? Or can we still keep it for use? According to the Certificate of Analysis, reagent B does not have an expiration date, does it mean that it can be used indefinitely?”
Hoping to find answers to our problems, I went online and was disappointed to find no straightforward solutions from the manufacturers. Instead, I had a surprise finding—there is a huge online community who is as confused as I am. A simple search on Research Gate revealed a countless number of questions relating to the use of expired reagents and advice to better manage inventories.
With continual changes in manpower and a lack of careful documentation, it is common for anyone who has worked long enough in a lab to have to deal with expired reagents. This article hopes to clarify some of the terminologies associated with expiration dates and the factors to consider when using expired reagents. It will also provide some tips to better manage inventories.
Expiration date terminology
Most of us are familiar with the word “expiry” which is defined by Oxford Dictionaries as “the end of the period in which something is valid.” However, manufacturers such as MilliporeSigma (Burlington, MA) and Lonza (Basel, Switzerland) have come up with a list of other terminologies, which is useful to know when managing expired reagents. Here are some of the more widely used terms used by MilliporeSigma:
Expiration or shelf-life dated product: This is a product which is expected to meet its specified properties only when stored under manufacturers’ defined conditions.
Recommended retest dated product: This is essentially the same as an expiration dated product. The catch is, however, that the expiration date may be extended following retest and review of product’s quality.
Product without retest or expiration dates: This is a product with no indication that it can become unstable, but product retest is recommended every few years for quality control.
Can expired reagents be used?
While most, if not all, manufacturers would recommend not using reagents past their expiration dates, those who have sufficient lab experience would agree that this is not always the best advice financially and scientifically. For instance, I had used antibodies that were at least three years past its expiration date—which is usually three to six months after first thawing—without any problem. There is an interesting study showing that antibodies can be used up to 26 years past their expiration dates. I also had a colleague who used only expired enzymatic solution for tissue digestion as she found it to be less harsh on cells.
The answer, in my opinion, regarding the use of expired reagents is risk-managing. There are a number of factors to consider before using expired reagents. When there is low risk of product degradation due to delivery and storage, unlikely contamination, and availability of simple methods to assess the properties of reagents, expired products can be used without qualms. The opposite also holds true. When there is huge uncertainty about the quality of expired reagents, it is not worth the risk to sabotage one’s experiment.
Minimizing risks from storage conditions
The storage conditions of reagents are always stated on the Certificate of Analysis or Materials’ Safety Data Sheet. Before using expired products, check whether their previous storage conditions are similar to that recommended by manufacturers. The more important storage conditions are temperature, light exposure, and humidity.
High temperature can affect the integrity of many biological reagents such as enzymes, which can become denatured and no longer bind to their targets. For products that should be stored frozen, the number of freeze-thaw cycles should also be minimal. Exposure to light affects the stability of fluorescent products such as dyes, which should be handled and stored only in the dark. Therefore, if an expired photo-sensitive reagent has been exposed to light continually, it should go into the bin.
Humidity is a storage condition that is often overlooked. As a PhD student in Los Angeles, I was surprised to find out that a chemical reagent known as poly-dimethyl-siloxane (PDMS) is still usable a year after it expired because back in Singapore where I also used PDMS regularly, the expired chemical no longer works. For reference, the humidity of Los Angeles is usually <10 percent while that of Singapore is typically >90 percent, and high humidity is known to accelerate the rate of chemical degradation. Unfortunately, Certificate of Analysis does not provide country or climate-specific expiry dates.
A general rule of thumb is that products in warmer and more humid climates are more susceptible to chemical instability and degradation. Hence, they should not be used too far after their expiration dates compared to products stored in drier climates. It is also useful to take note of seasonal changes, especially major climate events that could strongly influence temperature and humidity.
Minimizing risks from contamination
Contamination can be chemical or biological in nature. Chemical contamination can stem from the addition of substances that affects chemical purity, stability, and activity. For instance, acids and bases diluted with water are less stable than their concentrated counterparts as water can participate in chemical break-down. Hence, expired diluted products are generally not recommended for further use.
Biological contamination happens when microorganisms are introduced into products. Some of the more common contaminants include bacteria (such as the notorious mycoplasma) and fungi. These microorganisms thrive in cell culture media containing high concentrations of nutrients like glucose and amino acids. Cell culture media without supplements has an average shelf-life of one to two years and I have found expired products (up to six months past expiration date) to work just as well. However, it is not recommended to use media more than a year past its expiration date for culturing cells as it can have unknown biological effects.
Before you rush off to toss away the bottles of expired media lying somewhere in your fridge, you may want to know that while these expired products are not recommended for growing cells, they are perfectly good for washing cells during passaging. Nevertheless, it is necessary to take precautions to ensure sterility during media handling. For instance, expired cell culture media should be sealed or have been only exposed to air inside of a biosafety cabinet. Antibiotics may be added into expired cell culture media to kill potential microorganisms, but note that this practice may not work if the media is used to wash sensitive primary cells that hate antibiotics. The expired media should also be filtered using membrane of pore sizes smaller than microorganisms to eliminate biological contaminants before use. With good practices to maintain sterility, expired reagents can still be useful in their own ways.
Another factor to consider before using expired reagents is whether their properties can be easily validated. For instance, the strength of acids and bases can be conveniently determined with a pH meter. Unfortunately, many techniques to characterize materials’ properties, like mass spectrometry, are expensive and not readily available. Furthermore, manufacturers often do not provide experimental protocols and expected results from their analytical tests. For instance, the shelf-life of cell culture media without supplements is estimated to be one to two years, but manufacturers typically do not publish information on the techniques they use to determine expiration dates. This creates a disincentive for laboratories to invest effort for re-test. It also leads to more purchases, which is unfriendly to the environment. However, this can change if the scientific community collectively requests manufacturers to disclose relevant literature regarding expiration dates.
Managing chemical inventory
Earlier, I discussed ways to manage the risks of using expired reagents. However, we can all agree that with discipline and technological assistance, it is possible to avoid this problem.
Laboratories are mandated by the Environmental Health & Safety standards to keep a copy of the Materials’ Safety Data Sheet of all chemicals they own. An alternative use of such documentation is serving as records of products’ expiry dates alongside their corresponding delivery conditions and batch numbers. The practice of writing expected expiration dates with permanent ink on products is also a simple way to keep others informed.
Online platform such as Quartzy and HappiLabs allow laboratories to track the date of product arrival and first use. The information can be stored electronically and shared with all lab members. It also allows lab members to check for existing products in the inventory to streamline lab operations. In my opinion, a useful feature to add is scheduled notifications to alert users of reagents that are about to expire. This feature can also contribute to a safer working environment by minimizing potential risks of storing expired products.
Expired reagents are a common problem across laboratories. While it is easy to toss expired products away indiscriminately, it makes a lot more financial and scientific sense to evaluate whether they can still be of value. I hope that the next time you find an expired reagent in your lab, this article can help you decide what to do with it.
Andy Tay is a postdoctoral fellow in Stanford University. He can be reached at firstname.lastname@example.org
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