How stable are my reference materials after opening?
Unfortunately we are unable to advise on expiry and retest dates of reference
materials, or subsequent working solutions, after opening. It is the
responsibility of the user to ensure the integrity of the material once the seal
has been broken, as there are too many laboratory specific variables (usage
pattern, container, storage conditions, volume, dilution, solvent/matrix etc).
This view point is reinforced by section 5.7.4. of ISO Guide 34 (General
requirements for the competence of reference material producers), which
'The reference material producer shall ensure that the integrity of each
individual reference material unit is maintained until the seal has been broken
or up to the point when presented for analysis. The producer cannot be held
responsible for the material once the seal has been broken.'
Ideally solutions should be used shortly after opening the ampoule to avoid
concentration changes due to evaporation. Likewise, powders should not be stored
for any length of time after opening, due to the risk of water absorption from
There are a number of methods used by laboratories for assessing the integrity of
a reference material after opening. The frequency or approach may alter
depending on the drug and its properties.