Extraction of Water-Soluble Porphyrin and Metalloporphyrins into Acetonitrile by Salting-out

A cationic water soluble porphyrin (5,10,15,20-tetrakis (l-methyl-pyridinium-4-yl)porphyrin, $H_2tmpyp^{4+}$) and its metalloporphyrins (MP) were easily extracted into acetonitrile separated by addition of sodium chloride ($4mol\;dm^{-3}$) in the presence of sodium perchlorate, where M denotes $Zn^{2+}$, $Cu^{2+}$, $Co^{3+}$, $Fe^{3+}$, and $Mn^{3+}$ and $P^{2-}$ is porphyrinate ion. The extracted ion-pair complexes were completely dissociated to $[MP(ClO_4)_3]^+$, and $[MP(ClO_4)_2]^{2+}$. The extraction and the dissociation constants were determined by taking into account of the partition constant of sodium perchlorate ($K_D=1.82{\pm}0.01$). The chemical properties of the separated acetonitrile phase as $E_{T(30)}$ and $D_{II,I}$ were determined and compared with other water miscible solvents (acetone, actonitrile, 1,4-dioxane, tetrahydrofuran, 1-propanol and 2-propanol). Furthermore, a sensitive and selective method was proposed for the determination of a subnanogram amount of copper(II) in natural water samples by using the present salting-out method and the porphyrins.