Then the scientists pour the mixture, or "mobile phase" over the stationary phase. Sometimes, the scientists add a "binding buffer" to help the target molecule stick to its ligand. Then the scientists rinse away the rest of the mixture. The target molecule is stuck to its ligand, which is stuck to the stationary phase, so it is not rinsed away. Then the scientists add an "elution buffer" to make the ligand let go of the target molecule so they can collect it. Scientists sometimes use machines or special tools to hold the stationary phase in exactly the right position and to pour the mixture, rinse, and other treatments in exactly the right way.