A complex salt is not completely dissociated into its ions when added to water. Instead, they remain as complex structures. This complex formation is helpful in the chelation of metal ions. Here, the metal ions are bonded to chemical species called ligands through coordination bonds, resulting in the metal ion unavailable for any other chemical reaction that takes place in a reaction mixture. This is important in chemical reactions where interferences coming from certain metal ions should be removed.
However, a complex salt cannot be analyzed by dissolving it in water since complex salt does not give simple ions. A complex salt is prepared by mixing two different salts in a stoichiometric ratio. Then the correct amount of ligands will bind with the metal ion.