Recently, my colleagues and I faced a huge dilemma during the laboratory clean-up process. "Reagent A has expired. Should we throw it away? Or can we still keep it for use? According to the analysis, Reagent B has no shelf life. Can it be used indefinitely?"
Hoping to find the answer to our question, I went online, but I was disappointed that I did not find a direct solution from the manufacturer. On the contrary, I made an amazing discovery-there is a huge online community that is as confusing as I am. A simple search on Research Gate will reveal countless issues related to the use of expired reagents and suggestions for better inventory management.
Due to constant changes in manpower and lack of careful documentation, it is common for anyone who has worked in the laboratory long enough to deal with expired reagents. This article hopes to clarify some terms related to expiration dates and factors that need to be considered when using expired reagents. It will also provide some tips to better manage inventory.
Most of us are familiar with the term "expiry", and the Oxford dictionary defines it as "the end of the period of validity of something". However, manufacturers such as MilliporeSigma (Burlington, Massachusetts) and Lonza (Basel, Switzerland) have proposed lists of other terms, which are useful to understand when managing expired reagents. The following are some of the more widely used terms used by MilliporeSigma:
Expired or shelf life products: This product can only meet its specified characteristics when stored under the conditions specified by the manufacturer.
Recommended retest date products: This is basically the same as expired products. However, the problem is that after retesting and reviewing the quality of the product, the validity period may be extended.
Product without retest or expiration date: This is a product that has no indication that it will become unstable, but it is recommended to retest the product every few years for quality control.
Although most (if not all) manufacturers will recommend against using expired reagents, those with sufficient laboratory experience will agree that this is not always the best financial and scientific advice. For example, I have used antibodies that are valid for at least three years-usually three to six months after the first thawing-without any problems. An interesting study shows that the life of antibodies can be up to 26 years. Another colleague of mine only uses expired enzyme solution for tissue digestion because she found that it is less irritating to cells.
In my opinion, the answer to the use of expired reagents is risk management. There are many factors to consider before using expired reagents. When the risk of product degradation is low due to delivery and storage, unlikely contamination, and simple methods of evaluating reagent characteristics, expired products can be used without any worries. vice versa. When there is a huge uncertainty about the quality of expired reagents, it is not worth risking to sabotage your own experiments.
The storage conditions of the reagents are always stated in the certificate of analysis or the material safety data sheet. Before using the expired product, please check whether its previous storage conditions are similar to those recommended by the manufacturer. The more important storage conditions are temperature, light and humidity.
High temperatures can affect the integrity of many biological reagents (such as enzymes), which denature and no longer bind to their targets. For products that should be stored frozen, the number of freeze-thaw cycles should also be the least. Exposure to light will affect the stability of fluorescent products (such as dyes), and these products can only be handled and stored in the dark. Therefore, if the expired photosensitizer has been exposed to light, it should go into the trash can.
Humidity is an often overlooked storage condition. As a PhD student in Los Angeles, I was surprised to find that a chemical reagent called polydimethylsiloxane (PDMS) can still be used one year after its expiration date. When I returned to Singapore, I also often use PDMS. The chemical substance is no longer effective. For reference, the humidity in Los Angeles is usually less than 10%, while the humidity in Singapore is usually greater than 90%. It is well known that high humidity will accelerate the rate of chemical degradation. Unfortunately, the Certificate of Analysis does not provide a country- or climate-specific expiration date.
The general rule of thumb is that products in warm and humid climates are more susceptible to chemical instability and degradation. Therefore, compared to products stored in dry climates, they should not be used too long after the shelf life. It is also useful to pay attention to seasonal changes, especially major climatic events that may strongly affect temperature and humidity.
Pollution can be chemical or biological in nature. Chemical contamination may result from the addition of substances that affect chemical purity, stability and activity. For example, acids and bases diluted with water are not as stable as concentrated acids and bases because water participates in chemical decomposition. Therefore, it is generally not recommended to continue using expired diluted products.
When microorganisms are introduced into the product, biological contamination occurs. 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 such as glucose and amino acids. The average shelf life of cell culture media without supplements is one to two years, and I found that expired products (with a maximum validity period of six months) can be used normally. However, it is not recommended to use a medium beyond the validity period of more than one year to culture cells, because it may have unknown biological effects.
Before you hurriedly throw away the expired medium somewhere in the refrigerator, you may want to know that although these expired products are not recommended for culturing cells, they are very suitable for washing the cells during the passage. However, it is necessary to take precautions to ensure sterility during media handling. For example, expired cell culture media should be sealed or only exposed to the air in a biological safety cabinet. Antibiotics can be added to expired cell culture media to kill potential microorganisms, but please note that this approach may not work if the culture media is used to wash sensitive primary cells that hate antibiotics. The expired media should also be filtered with a membrane with a pore size smaller than that of microorganisms to eliminate biological contaminants before use. By maintaining sterile good practices, expired reagents can still function in their own way.
Another factor to consider before using expired reagents is whether their properties can be easily verified. For example, the strength of acids and bases can be easily measured with a pH meter. Unfortunately, many techniques for characterizing material properties (such as mass spectrometry) are expensive and difficult to obtain. In addition, manufacturers usually do not provide experimental protocols and the expected results of analytical tests. For example, the shelf life of cell culture media without supplements is estimated to be one to two years, but manufacturers usually do not publish the technical information they use to determine the expiration date. This prevents laboratories from investing energy in retesting. It also leads to more purchases, which is not friendly to the environment. However, if the scientific community collectively requires manufacturers to disclose relevant literature on expiration dates, this may change.
Earlier, I discussed ways to manage the risk of using expired reagents. However, we all agree that through discipline and technical assistance, this problem can be avoided.
Environmental health and safety standards require laboratories to keep copies of material safety data sheets for all chemicals they have. Another use of this type of document is to record the expiry date of the product and the corresponding delivery conditions and batch number. The practice of writing down the expected expiration date in permanent ink on the product is also an easy way to keep others informed.
Online platforms such as Quartzy and HappiLabs allow laboratories to track the date of product arrival and first use. This information can be stored electronically and shared with all laboratory members. It also allows laboratory members to check existing products in inventory to simplify laboratory operations. In my opinion, a useful feature to add is scheduled notifications to remind users of reagents that are about to expire. This feature can also contribute to a safer work environment by minimizing the potential risk of storing expired products.
Expiration of reagents is a common problem in laboratories. Although it is easy to throw away expired products at will, it is more economic and scientific to evaluate whether they are still valuable. I hope that next time you find an expired reagent in the laboratory, this article can help you decide what to do with it.
Tags: Health and Safety Management Skills for Testing, Kits and Reagent Chemical Inventory Management
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