in the case of cobalt and 2-nitroso-1-naphthol-4-sulphonic acid ( nitroso-nw acid ) , the most suitable counter-cation is the tetrabutylammonium ion ( bu ( 4 ) n ( + ) ) : in this case only the ion-pair of the anionic cobalt chelate is extracted into chloroform and the excess of the nitroso-nw acid remains in the aqueous phase .
C0022023
ion
C0003075
anionic