Final answer:
The appearance of crystals in mannitol injections generally indicates that the product was exposed to excessive cold, which can cause the mannitol to crystallize out of the solution due to a supersaturated environment.
Step-by-step explanation:
The appearance of crystals in mannitol injections would indicate that the product was exposed to excessive cold. This condition can cause the mannitol, which is normally in a dissolved state, to crystallize or precipitate out of solution. When a liquid solution of mannitol is exposed to low temperatures, it may create a supersaturated environment where there is more solute than can be dissolved, leading to crystal formation.
Re-crystallization is a process that can sometimes be used to purify solutes, where the pure substance crystallizes out and leaves the impurities in solution. However, in the context of mannitol injections for medical use, the appearance of crystals is typically not associated with re-crystallization for the purpose of purification but rather with exposure to incorrect storage temperatures. Therefore, if mannitol injections exhibit visible crystallization, it would likely suggest that the product's storage conditions have not been maintained correctly, rather than issues relating to impurities or the formulation process with sterile saline.