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Abstract The present work consists of two parts. The first part IS directed to develop new spectrophotometric methods for the determination of zinc(ll). Two methods based on micelle-enhanced absorbance of the zinc-hematoxylin and zinc-murexide complexes were developed. The second part of the work is directed to the application of the iodide ion-selective electrode as sensor in the potentiometric determintion of silver(!), palladium(ll) and gold(lll) in their binary mixtures, by titration with standard potassium iodide solution. The influence of pH on the shape of the titration curves of the former metal ions was investigated and the effect of some masking agents was studied. To determine binary mixtures of those metal ions, t’11o-step procedures based on titrating increments of the mixtures at two different pHs or by titration in the presence and absence of masking agents, were proposed. The first spectrophotometric method for zinc(ll) deter- mination IS based on reaction with hematoxylin to form a 1:2 binary complex m aqueous medium. at pH 7.8-8.2. The molar absorptivity of the complex was 4.5 x 4 -1 -1 10 !.mol .em at 600 nm. A study of the influence of cationic, anionic and nonionic surfactants on the absorbance of the binary complex indicated that maximum sensi- tization of the colour reaction was obtained m the presence of the cationic surfactant, cetyltrimethylammonium bromide (CT.’\B). The molar abs,xpti\ 1:\. of the sensitized complex. m the presence. of CTAB, was 6.3 x 104 -1 -1 at GIG nm. The optimum pH range for the complex formation was found to be 7.3-8.0. Beer’s Jaw was obeyed up to 0.85 and 0.92 ppm of zinc for the methods based on binary and sensitized complex formation, respectively. The corresponding values of the sensitivity index were 0.0015 and 0.0010 )Jg.cm-2 . To determine zinc in aluminium metal and aluminium base alloys, using the sensitized hematoxylin reaction, a preliminry solvent extraction separation of zinc from 2M hydrochloric acid rc.ed1um with tri(iso-octyllamine in isobutyl methyl ketone was carried out. The results obtained for the determination of zinc in an aluminium metal, three aluminium-silicon alloys and tv•o aluminium-zinc-copper alloys were in good agreement with the certified values. The second method whirh was proposed for the spectrophoto- metric determination of zindll) utilized murexide as reagent. The cationic surfactant, cetylpyridinium bromide (CPB), proved to be the optimum sensitizer for the zinc-murexide reaction. .>\ddition of this surfactant to the binary complex shifted the wa,e’ength of the absorption maximum from 460 to 47S nm and increased the molar absorptivity more than two-folds. The optimum pH ranges for the formation of the bmary and sensitized complexes were S.c-8.5 and 7.7-8.4, respecti,ely. The corresponding molar absorp:l\ nies of the chelates were 2.1 x ’· and 4.7 x IG u -1 -. .em-. The effect of murexide and CPB concentrations and standing time were. investigated. The continuous variation method indicated a 1:2 metal- reagent ratio in the binary and sensitized complexes. The methods based on the formation of the former chelates adhered to Beer’s law up to 1.96 and 1.44 ppm of zinc, respectively. The sensitivity index of the methods was 0.0033 and 0.0014 )Jg.cm-2, respectively. The influence of diverse ions on the selectivity of the sensitized zinc-murexide reaction was investigated and some masking agents were recommended. The method was successfully applied to determine zinc in aluminium metal, aluminium-silicon, aluminium- magnesium, aluminium-copper, and aluminium-zinc-copper alloys. The advantage of this method is the omittance of the extraction step of zinc in real samples, by proper masking of interfering ions. the second part of the present work was directed to develop potentiometric methods for the determination of silver(!), palladium(Il) and gold(lll) in their individual solutions and in binary mixtures. Determination of the individual metal ions were performed by titration with 1 x 10-2M potassium iodide solution using the iodide ion-selective electrode as sensor. Study of the effect of analate pH on the shape of the titration curves, position and value of the potential breaks at the end points, indicated that the optimum pH ranges were 2.0-10.0 (Ag-), 1.8-3.2 (Pd 2 ), and 1.7-2.5 (Au 3+). Thus, pH 2.0 was selected m the procedures for the determination of silver(!), palladium(Il), and gold(Jll) to simplify the conditions. At the end poim, in the potentiometric titration of the former metal ions,. one, two and three equivalents of the iodide ion were consumed per mole of silver(l), palladium(ll) and gold(IIJ), respectively. A study of interference due to foreign ions was performed usmg the procedure based on titrating silver(!) with iodide solution. L’p to 100-fold molar excess of AJ(lll), Ba(II), Cd(ll), Ca(II), Cu(ll), Fe(IJ). Fe(IIll, Mg(ll), Ni(II), Zn(II), NH: , No; , citrate and oxalate did not interfere. In the presence of up to 100-fold excess of chloride or bromide ion, the position of the end point break was not altered. However, the potential break decreased to be 135 and 60 mV, respec- tively. On the other hand, the presence of 100-fold molar excess of thiocyanate with silver(!), or either citric acid or dim thyl glyoxime with palladium(II) obsecured the end points. Thus, potassium thio- cyanate could be used as masking agent for silver(!), whereas citric acid or dimethyl glyoxime were utilized to mask palladium(II). Taking advantage of the different pH ranges necessary for conducting the potentiometric titration of silver(!). palladium(Il) and gold( Ill), a two-step procedure for the determination of silver- palladium or silver-gold binary mixture was proposed. In the first step. an increment of the mixture, at pH 2.0. was titrated with the io1ide solution. At the end point. the volume of titrant is equiva- lent to the total metal ions m solution. The second step of the proc·edure ’’’as based 0:1 titrating another increment of the mixture at pH 9.0. :\t this pH, the volume of titrant added at the end point is equn alent to sil ver(I) only.. Another method for the determination silver(!), palladiu”n(II) and gold(III) in their binary mixtures ”·as also su3gested. The method was based on masking silver(l) with thiocyanate and masking paJJa dium(ll) with citric acid or dimethylglyoxime. :\ two-step procedure was performed by titrating increments of the mixtures in the presence and absence of the masking agent. Satisfactory results Wel”e obtained for the analysis of those metal ions in binary mtxtures. |