The question of whether expiry dates should be assigned to reference substances is of great importance both to the users and to the distributors of the substances. The arguments against expiry dating are that it might lead to the unnecessary discarding of satisfactory materials and that considerable experimental work would first have to be carried out to make the setting of meaningful expiry dates possible.

If it is considered necessary to specify an expiry date in a particular case, the date should be stated on the label. At present, most reference substances are replaced by new batches only when this has been shown to be necessary by re-evaluation. This procedure minimizes unnecessary waste of valuable materials, but in order to make it completely satisfactory it would be necessary to devise effective means of informing analysts in possession of reference substances about any replacement of batches.