ABSTRACT
The procedure used in establishing a sensitive
spectrophotometric method for the determination of
nickel in trace level is described.
The method involves the use of a long chain
quaternary ammonium salt, cetyltrimethylammonium
bromide as a surfactant and Xylenol orange as an
indicator.
To arrive at the method, first the optimum conditions
for the interaction between the cetyltrimethylammonium
bromide (CTAB), xylenol orange (XO) and metal ions were
established.
Then the nickel complex Ni-XO-CTAB was chosen for further
study.
The conditions for the increased absorbance of the nickel
complex were established by observing the U.V. absorbance
of the complex.
The results show that the Xylenol orange (XO) and
cetyltrimethylammonium bromide (CTAB) interact at pH 10.5
to form stable systems having X0:CTAB mole ratios of 1:2 and
1:6.
The formulae of the systems should be [x0 {CTAB)2]
n
and [X0(CTAB)6] n where n is an interger.
iii
The nickel complex was found to have a maximum
absorbance at 622 nm with a molar extinction coefficient
of 6.14 x 104 i. mole-1 cm1′
The composition of the nickel complex was studied
using the mole ratio method. The mole ratio of Ni:XO in
the complex was found to be 1:4.
The formula of the nickel complex should then be Ni
[XO (CTABT)2]4 and Ni[XO (CTAB)6]4 for the two established
XO: CTAB systems.
The selectivity of the method was studied by observing
the absorbance of nickel complex of known concentration
of nickel in pure nickel solution and in the presence of
some other metal ions.
This study reveals that the selectivity of the method is
limited due to interference from ion, cadmium and cobalt ions.
No attempt was made in this study to mask the interfering
ions.
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