I will be traveling far to receive the urine and therefore won’t be able to put them directly into the - 80 degree.s. How long do you think its ok to keep them on ice until freezing? I want to extract exosomes for wetsern blot at a later time.
Depending on your opportunities. In my opinion, some hours should be no problem (depending on your targets, such a proteins vs. chemical compounds). An alternative idea would be using a thermos tank with liquid nitrogen.