Perchloric acid cadmium complexes

Armannsson [659] has described a procedure involving dithizone extraction and flame atomic absorption spectrometry for the determination of cadmium, zinc, lead, copper, nickel, cobalt, and silver in seawater. In this procedure 500 ml of seawater taken in a plastic container is exposed to a 1000 W mercury arc lamp for 5-15 h to break down metal organic complexes. The solution is adjusted to pH 8, and 10 ml of 0.2% dithizone in chloroform added. The 10 ml of chloroform is run off and after adjustment to pH 9.5 the aqueous phase is extracted with a further 10 ml of dithizone. The combined extracts are washed with 50 ml of dilute ammonia. To the organic phases is added 50 ml of 0.2 M-hydrochloric acid. The phases are separated and the aqueous portion washed with 5 ml of chloroform. The aqueous portion is evaporated to dryness and the residue dissolved in 5 ml of 2 M hydrochloric acid (solution A). Perchloric acid (3 ml) is added to the organic portion, evaporated to dryness, and a further 2 ml of 60% perchloric acid added to ensure that all organic matter has been... 

Demetallation of zinc, cadmium, and mercury(II) sarcophaginates has rather efficiently been examined by NMR spectroscopy. The data on proton exchange obtained by this method indicate that [Zn(diAMHsar)]4+ cation is stable towards 2M deuterated perchloric acid, and only partial proton exchange has been observed. In deuterated hydrochloric acid at an equal concentration, the same complex decomposes, and proton exchange in this case proceeds more rapidly than that in perchloric acid at an equal concentration, and the extrusion of the Zn + ion occurs. For [Cd(diAMsar)]2+ dication in DCl, the proton exchange and the extrusion of the Cd + ion occur simultaneously. 

Calcium(II), which shows no appreciable complexing, has a distribution coefficient of 147 in 0.5 M perchloric acid and 191 in 0.5 M hydrochloric acid. Strelow. Rethc-meyer, and Bothnia [10] also reported data for nitric and sulfuric acids that showed complexation in some cases. Mercury(II), bismuth(III), cadmium(II), zinc(II), and lead(II) form bromide complexes and are eluted in the order given in 0.1 to 0.6 M hydrobromic acid [11]. Most other metal cations remain on the column. Aluminu-m(III), molybdenum(VI), niobium(V), tin(IV), tantalum(V), uranium(VI), tung-sten(VI), and zirconium(IV) form anionic fluoride complexes and are quickly eluted from a hydrogen-form cation-exchange column with 0.1 to 0.2 M HF [12]. 

The data for hydrochloric acid [3] indicate selective complexing between metal cations and the chloride ion. For example, cadmium(ll) has a distribution coefficient of 6.5 in 0.5 M hydrochloric acid, but aD - 101 in 0.5 M perchloric acid. 

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