organic cation quaternary ammonium ion a quaternary ammonium CHEBI:8693 quaternary ammonium ions quaternary ammonium ion quaternary ammonium ion A derivative of ammonium, NH<small>₄</small><small>^+</small>, in which all four of the hydrogens bonded to nitrogen have been replaced with univalent (usually organyl) groups. CHEBI:26470 Quaternary amine ammonium ion derivative