When Standards Are Not Stable As Desired

Hi All,

I just wanted to know what would be the most appropriate thing to do when during an analytical method validation, your data showed that your standards are only stable for 3 days at room temp? Your superior is however adamant that it could be stable for at least one week. So now they want to re-test standard stability. Is this the right thing for them to do even though my original data is deemed valid and reliable (despite the fact that it only supports a 3-day stability timeframe)? A retest to me just seems like we’re “picking and choosing” data to achieve desired results. Let’s say that new data is generated (and regardless of whether or not the retest results agree/disagree with my results), what should I do with my initial set of results (the ones that demonstrated that the standards are only stable for 3 days at RT)? Hope that makes sense. Please help. Thanks


You need to do an investigate. If there is literature that justifies 1 week, then an OOS would be required. The material could have lost it stability due to many reasons. One may be that the room temperature may be too high or is your lab temperature control and monitored. If not this may be one means of invalidating the data. Other factors is that maybe there was a contaminant in the preparation that changed the pH. Another being that the system may not be suitable.
As an advice, I always perform the stability of solution at room temp for 24 hours and in the fridge (2 to 8 C) for more than a week. As a good practice if an analyst is to use sample for longer than 24 gours he should place it in the fridge.