Splitting up dry chemicals is generally a bad idea, since the individual components may not be evenly mixed throughout the entire can. You could possibly mix the entire can at a higher concentration (it'll keep better), and then cut it from there, but having had no experience doing that, I'm not sure how well it'll work.

If you're confident that the dry chemicals are well mixed, just divide it up and pack in air-tight containers. There will always be some air in the container (unless you remove it), so oxidation will occur, but perhaps the life will be extended.

Good luck!