Easy. The firs chance is after you got the first ADAM from a Little Sister (not matter how) follow the way to the next Mission Point, which is to find a Gatherer's Gardenn and buy the Fire Plasmid. If you have found Gatherer's Garden buy just the Fire Plasmid and nothing else.
Go to the enttrance of the room but do not leave. If you see the door, look to your left where you can see a way blockd by ice, melt it with your new Fire Plasmid and go into the now opend room where is a second Gatherer's Garden. All you need to do now, is to buy a TONIC SLOT with the rest of Adam that you have and then you should get the Achievment.
Hope that helps!!!