Flexible Expiration Dates?
At Inorganic Ventures, we typically do everything we can to flex to your specs — from rush manufacturing to full product customization. However, we draw the line at flexible expiration dates - scientifically speaking, there is no such thing.
We have been vocal supporters of a one-year expiration date on most inorganic certified reference materials. For over fifteen years, we've conducted chemical and physical stability studies on everything we make. These studies are an important part of our quality control efforts. Our data confirms the need for conservative, responsible expiration dates.
But why won't a longer expiration date fly? Let's take a closer look.
Chemical Stability—virtually infinite
The vast majority of standards are chemically stable for periods well in excess of three (3) years. In almost all cases, we have not detected any form of chemical instability. The data suggest that a well-designed standard will be chemically stable forever. Unfortunately, expiration dates are dependent upon other factors besides chemical stability.
Physical Stability—1-2 years
With the exception of products that are distributed in flame-sealed glass ampoules, all containers transpire and are therefore physically unstable. The transpiration rate increases with use of the standard.
Twenty-one months is the longest a 125mL bottle of standard can remain on the shelf (having never been opened) and still remain within the certified value. This assumes an uncertainty of 0.5% relative (a 500mL bottle is physically stable for four years). With regular use, the amount of time that the standard remains within certification will decrease. This data is based on a function of the vapor space above the liquid and the number of times opened. Thus, you can begin to understand why granting even a full year before expiry is not always possible, especially for volumes less than 125mL.
Human Error—1 year (or less)
In addition to Transpiration (physical instability), mistakes happen. The longer a standard is in use, the greater the risk of a mistake occurring. This is analogous to driving without a seatbelt - while doing so is considered unsafe, you'll remain unharmed until someone makes a mistake that causes a serious accident. And the more time you spend on the road, the greater your chances of being involved in an accident. Similarly, the more time a standard remains in laboratory use, the greater the chances it will be contaminated through human error.
"The increasing risk of human error only reinforces the argument for a shorter expiration date, not a longer one."
The reality of transpiration prevents the use of expiration dates longer than one year based upon the ongoing scientific studies conducted by our laboratory, as well as others. The increasing risk of human error only reinforces the argument for a shorter expiration date, not a longer one.
Statements directing an analyst to use a standard for any period of time must be supported by scientific data that demonstrate both chemical and physical stability. We're happy to make our research available to the public. Others might mix words and manipulate the data to make you believe that two or even three years is an acceptable expiration date. But facts are facts. We cannot in good faith endorse an extended expiration date. Our customers deserve a reliable product. Our inflexible expiration dates ensure that they'll get one.