I am doing a FACS method validation using cell lysate and came across this issue of need to validate the long term stability if temperature changes during storage. Since cell lysate are kept in liquid nitrogen, the baseline is to keep samples in LN2. But the samples need to shipped abroad and during shipment it will be stored at -80 degrees celcius. After shipment when arrived to the lab, if the samples are to be stored in the liquid nitrogen tank, then would this course of temperature change need to be validated? I am planning to validated the long-term stability at -80 degrees celcius and in LN2 tank for at least 6 months. Would it be necessary to validate LN2 tank 1month then -80 degrees celcius 1 week then LN2 tank 1 month to properly validate the method? Or would it be ok just to validated -80 and LN2 tank each at 1 month and 6 months?