Why are some of my RNAprotect-stabilized samples frozen at 0ºC while others are not?

Different samples of varying water content may affect the point at which the reagent will form a solid at low temperature. Other factors can be temperature variation from freezer to freezer, or even within the same freezer (e.g., different temperatures near the door and in the back region of the freezer). Regardless, the performance of the RNAprotect Tissue Reagent and the RNA quality are not affected by freezing of the reagent.