Electrochemical masking for removal of the titanium matrix effect in DPASV determination of thallium

The possibilities for eliminating the matrix effect caused by large concentrations of titanium in an EDTA-based electrolyte have been examined. In these solutions titanium gives a DPASV peak, the height of which decreases with increase in preconcentration time. This effect depends on the pH and is probably caused by impurities in the EDTA. Complete damping of the titanium peak by means of this effect is not possible. The influence of the following surfactants on the DPASV peak for titanium in 0.2M EDTA at pH 4.5 was investigated: polyoxyethylated alkylphenols having an average of 3 and 9.5 ethylene oxide sub-units; polyoxyethylene alcohols having an average of 5 and 20 ethylene oxide sub-units; polyoxyethylene (glycerol mono-oleate) ether having an average of 20 ethylene oxide sub-units; polyoxyethylene (sorbitol mono-oleate) ether having an average of 20 ethylene oxide sub-units; poly(ethylene oxide) having M.W. 5.0 x 10(6); poly(ethylene oxide)poly(propylene oxide) block copolymer having M.W. 1.625 x 10(4); N,N,N,N',N',N'-hexamethylhexamethylenediammonium bromide (HMB); benzyl(diisobutylphenoxyethoxy) dimethylammonium chloride; hexadecyltrimethylammonium bromide; tetrabutylammonium chloride (TBAC); hexadecyldimethylbenzylammonium chloride, hexadecyltributylphosphonium bromide; tetraphenylphosphonium bromide; sodium dodecylsulphate; sodium stearate; sodium dodecylbenzenesulphonate; sodium octadecyloxyethylene ether sulphate; sodium octadecyloxyethylene ether malonate (Malester). Except for TBAC and HMB all the surfactants investigated decreased the titanium peak, although to different degrees. Generally the effect increased in the sequence cationic surfactants < non-ionic surfactants < anionic surfactants. The more hydrophobic non-ionic surfactants decreased the titanium peak more strongly than did the less hydrophobic ones. Malester was found the best of the investigated surfactants for this purpose. Sodium dodecylbenzenesulphonate also gave good results, although in this case an additional peak appeared. In the presence of these last two surfactants iron(III) does not substantially disturb the base-line current.