ION-PAIR EXTRACTION OF METALLOPORPHYRINS INTO ACETONITRILE FOR DETERMINATION OF COPPER(II)

Equilibrium study of ion-pair extraction of a cationic water-soluble p orphyrin 15,20-tetrakis(1-methyl-pyridinium-4-yl)porphyrin, H(2)tmpyp( 4+)] and its metalloporphyrins (MP) into the acetonitrile layer, separ ated by addition of sodium chloride (4.00 mol dm(-3)) to a 1:1 (v/v) a cetonitrile-water mixed solvent, was carried out to develop a new and useful method for the determination of a subnanogram amount of copper( II). M denotes Zn2+, Cu2+, Co3+, Fe3+, and Mn3+, and P2- is porphyrina te ion. The extraction and dissociation constants of the ion-pair comp lexes, defined by K-ex = MP(ClO4)(4)](org)-[MP(4+)](-1)(aq)[ClO4-](-4) (aq), K-dis,K-1 = 4)(3)(+)](org)[ClO4-](org)-[MP(ClO4)(4)](-1)(org), a nd K-dis,K-2 = )(2+)](org)[ClO4-](org)-[MP(ClO4)(3)(+)](-1)(org), were determined by taking into account the partition constant of sodium pe rchlorate (K-D = 1.82 +/- 0.01). The equilibrium constants were found to be KexKdis,1 = (7.2 +/- 1.3) x 10(4), (6.4 +/- 0.9) x 10(4), (1.35 +/- 0.13) x 10(5), (4.8 +/- 0.6) x 10(3), (1.23 +/- 0.05) x 10(4), and (1.42 +/- 0.07) x 10(3) at 25 degrees C for the free base porphyrin ( H(2)tmpyp(4+)) and the metalloporphyrins of zinc(II), copper(II), coba lt(III), iron(III), and manganese(III), respectively. The K-dis,K-2,a values were (2.9 +/- 1.4) x 10(-2), (3.1 + 1.1) x 10(-2), (8.0 +/- 4.9 ) x 10(-3), and (5.1 +/- 2.2) x 10(-2) for the free base porphyrins an d the metalloporphyrins of zinc(II), copper(II), and cobalt(III), resp ectively. The results were developed for determination of a trace amou nt of copper(II) (3 x 10(-8)-4 x 10(-6) mol dm(-3)) in natural water s amples using H(2)tmpyp(4+) with a molar absorptivity of 3.1 x 10(5) mo l(-1) dm(3) cm(-1) at a precision of 1.3% (RSD). The determination of copper(II) was not interfered by the presence of 10(-4) mol dm(-3) of Mn2+, Co2+ Ni2+, Hg2+, Cd2+, Ag, Cr3+, V5+, Al3+, Mg2+, Ca2+, Br-, I-, SCN-, and S2O32- and 10(-5) mol dm(-3) of Fe3+, Zn2+, and Pd2+.