Welcome to the forum Jago.
If you are transporting any typical fish or plant sample, simply fill your container with 2/3 air and 1/3 water. The sloshing about that happens quite naturally will keep enough oxygen in the water for the occupants for quite some time. I use that ratio to bag fish for sale at 4 AM and I expect them to still be in good condition when the buyer arrives home with them at 10PM. If you are shipping, you may want to add some pure oxygen but for a short trip like 16 to 18 hours, the oxygen can be easily maintained by simply using appropriate ratios of air and water.