Activating effect of ligands in the catalyzed reactions and its application to the catalytic determination of trace amounts of elements

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A spectrophotomeric flow-injection method has been developed for the successive determination of copper(II) and iron(III). It is based on the catalytic effect of copper(II) and iron(III) on the hydrogen peroxide oxidation of N,N'-bis(2-hydroxy-3-sulfopropyl)-o-tolidine (HTS) to produce an intensely colored dye (λ_<max> = 670 nm). In the copper(II)-catalyzed reaction, 2,2'-biquinoline, 2,9-dimethyl-4,7-diphenyl^1, 10-phenanthroline disulfonic acid and 2,9-dimethyl-phenanthroine (neocup) were found to be effective activators. On the other hand, 2,2'-bipyridine, 1,10-phenanthroine (phen) and 8-hydroxquinoline-5-sulfonic acid acted as activators in the iron(III)-catalyzed reaction. By introducing the sample solution containing neocup or phen into flow line in the presence of phosphoric acid and triethanolamine as masking agents, copper(II) (1-30 ng ml^<-1>) and iron(III) (2-50 ng ml^<-1>) can be selectively determined with sampling frequency of 20 h^<-1> without any separation procedures.A sensitive flow-injection photometric method has been also proposed for the catalytic determination of vanadium(IV, V), based on the catalytic effect of vanadium(IV, V) on the oxidation of HTS by bromate. The presence of 1,2-dihydroxybenzene-3,5-disulfonate increased the rate of vanadium(IV, V)-catalyzed reaction and significantly enhanced the sensitivity the method. Vanadium(IV) and vanadium(V) in the range 0.01-3.0 ng ml^<-1> were easily determined with sampling rate of about 30 h^<-1>. The limit of detection (S/N = 3) was 0.01 ng ml^<-1> and the relative standard deviations were 1.4 % and 1.6 % for ten determinations of 0.2 ng ml^<-1> vanadium(IV) and vanadium(V), respectively. Interferences from metal ions could be suppressed by the use of ethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid) as a masking agent. The proposed method was successfully applied to the determination of vanadium in water samples.