الفهرس 
Materials:
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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.