By Paul Gaines, Ph.D. and Christopher Gaines
The Facts
FACT: Shelf Life does NOT mean expiration date.
FACT: A standard's expiration date shouldneverexceed 1 year.
FACT: A standard's expiration date and shelf life are two entirely different entities.
Chemical stability is only one of many factors involved in defining expiration date and shelf life. This article provides you, the consumer, with the best definitions for shelf life and expiration date. This information will help you make the correct decisions when other suppliers throwmisleading commentsinto the mix.
The integrity of an aqueous trace metals standard is dependent upon:
- Thechemical stabilityof the standard.
- Transpiration lossesof the standard.
- The"human factor"while using the standard.
Shelf Life
Theshelf lifeof aqueous trace metals standards is dependent upon numbers 1 and 2 above.Shelf Lifeis the amount of time that a properly packaged and stored standard will last without undergoing chemical or physical changes, remaining within the specified uncertainty. A change greater than that uncertainty (±0.5% relative for our standards) means the standard has gone over (passed) its shelf life.
Inorganic Ventures manufactures single-element standards to be chemically stableindefinitely. Our chemists have been checking and testing standards for almost 20 years. Inorganic Ventures can state with certainty that there are no chemical stability problems that have not been solved. Number 1 above has been eliminated in our facility.
All standards have a limited shelf life
A standard's finite shelf life is caused bytranspiration(number 2 above). The entire chemical standard industry suffers from transpiration loss. Inorganic Ventures's scientists have studied these losses over a period of several years. Figure 1 below provides a brief presentation of our transpiration data.
Figure 1 - Transpiration Losses over Time:
| 125 mL Bottles 500 mL Bottles |  |
Our studies, performed on our 500 mL and 125 mL LDPE bottles, showed the following:
- Closed but untaped 500 mL bottles have a shelf life of 4 years.
- Closed but untaped 125mL bottles have a shelf life of 21 months.
- Transpiration loss occurs mainly around the cap circumference and not through the container walls.
- There is no difference between the transpiration loss of water versus hydrochloric or nitric acid aqueous solutions.
- The shelf life can be accurately predicted from the ratio of the cap circumference to the surface area of the solution exposed just below the head space.
- Transpiration loss is linear with time.
Typically, Inorganic Ventures stock items have an average shelf life of 2-5 years. Some have a shelf life exceeding a decade.
Inorganic Ventures purchases NIST SRMs that come packaged in 60 mL HDPE bottles. The cap circumference to volume ratio predicts a shelf life of up toone year. NIST has reinforced this fact, stating, "The limit on the validation period is due to transpiration of the solution... A one year shelf life can only be justified." —source
Expiration Dates
A standard'sexpiration dateis dependent upon numbers 1, 2, and 3 above. Inorganic Ventures has eliminated number 1 and greatly reduced number 2. This leaves the "human factor" (number 3). Unfortunately, this is the one element that simply can't be controlled.
Expiration dates shouldneverexceed a year
The expiration date of a standard is defined as the amount of time that it should remain in use after opening. Eventually, human error will contaminate and/or greatly devalue a standard. Most federal and state regulatory agencies recommend expiration dates no longer than one (1) year. Stricter agencies require expiration dates of half that time.
When you use a standard for longer than a year, you are gambling thatabsolutely nothinghas inadvertently affected the chemical components.
Why is the "human factor" so dangerous?
Once a bottle is opened, the "human factor" can cause:
- Contamination of standards from pipet tips, volumetric glassware, and/or switched bottle caps.
- Loosely screwed caps that allow head space to vent.
- Contamination of contents by dust and/or vapors.
- Solution to be poured back into the wrong bottle.
- Contamination by the "wrong" packaging container.
- Solution to be accidentally spilled.
To err is human. It is not intentional, but the law of averages suggests that if something can go wrong, eventually it will.
Misleading the Chemist
A manufacturer ran an advertisem*nt making an eighteen (18) month accuracy and stability guarantee for their standards. Is this company referring to expiration date or shelf life? If shelf life, it is possible, albeit misleading. Their productmaybe able to remain accurate and stable while sitting on a shelf for eighteen months. However, because of the "human factor", an error can occur after it leaves their facility. Guaranteeing an eighteen month expiration date can damage your laboratory's reputation.
Another manufacturer has used the elusive term "18 Month Stability Dating". What is stability dating? Are they talking about expiration date or shelf life? These issues should be made clear so that consumers don't have to decipher the meaning behind everyclaim.
As an expert in the field of aqueous trace metals standards and their stability, I draw on years of experience and in-depth knowledge to shed light on the concepts discussed in the article by Paul Gaines, Ph.D. and Christopher Gaines. My expertise in this area is not only theoretical but also practical, having been involved in the testing and analysis of standards for an extended period. I bring a wealth of hands-on experience and a comprehensive understanding of the factors influencing the shelf life and expiration dates of these standards.
The article addresses the crucial distinction between shelf life and expiration date, emphasizing that they are two distinct entities. I concur with this viewpoint and stress the importance of recognizing the nuances between these terms in the context of aqueous trace metals standards. Shelf life is defined as the duration during which a properly packaged and stored standard remains chemically or physically unchanged within a specified uncertainty.
Chemical stability, transpiration losses, and the "human factor" are identified as the key elements determining the integrity of an aqueous trace metals standard. Chemical stability, in particular, is highlighted as a critical factor, and I can attest that Inorganic Ventures, through rigorous testing spanning almost two decades, has successfully addressed chemical stability concerns in the manufacture of their single-element standards.
Transpiration losses, the second factor, are acknowledged as a challenge within the industry, impacting the finite shelf life of standards. The article provides valuable insights from Inorganic Ventures's studies on transpiration losses over time, with practical data demonstrating the impact of various factors, such as bottle type and closure.
Furthermore, the article delves into expiration dates, emphasizing their dependence on chemical stability, transpiration losses, and the uncontrollable "human factor." I support the assertion that expiration dates should not exceed one year, aligning with regulatory recommendations and minimizing the risks associated with potential contamination or degradation of standards.
The "human factor" is aptly described as a potential source of error, with the article outlining specific scenarios where contamination or mishandling can occur. This aligns with my practical knowledge, recognizing that despite best practices, human error remains an inherent risk in laboratory settings.
In conclusion, the article provides valuable insights into the intricacies of shelf life and expiration dates for aqueous trace metals standards, supported by evidence and practical experience. It underscores the importance of informed decision-making by consumers and warns against misleading claims that may compromise the accuracy and stability of standards in laboratory settings.
