An amine is a basic compound. It is protonated in the presence of excess HCl forming a salt that is soluble in aqueous solution. This is how you separated the amine from the original mixture containing it.
An amine is soluble in acidic aqueous solution because it forms a salt, an ionic form. However, if you change the pH of the solution to basic the amine can no longer stay dissolved because it is no longer ionic! This process is called basification.
Basification is done by carefully adding concentrated NaOH solution to the solution containing the amine salt until it becomes basic.
Organic Web Chem University of Alberta
