Figure 8 – Formation of ion association complexes between [BiJ
4
-
] anions and
polymethine dye Astra Phloxine.
C
HCl
= 0.1 mol L
-1
; C
KJ
= 6.5 mmol L
-1
; C
Dye
= 10 μmol L
-1
; Bi(III) concentration, μmol L
-1
:
1 – 0; 2 – 0.5; 3 – 1; 4 – 2; 5 – 3; 6 – 4
In most of these works, authors have stabilized low-soluble IAs by addition of
appropriate amounts of solubilizer such as polyvinyl alcohol or non-ionic surfactants.
However, in several papers it was mentioned that in definite conditions solutions of
IAs were stable without addition of solubilizer.
We have found several other systems in which aggregation of dye was provoked
by the formation of low-soluble IAs of iodide metal complexes with cationic dyes. The
change in color during the reaction of polymethine and rhodamine dyes was detected
during the reaction with iodide complexes of bismuth(III), mercury(II), cadmium(II),
antimony(III), and tin(II). The changes in the spectra were quite similar to those
observed in the case of HPA.
The optimal conditions for the determination of bismuth(III), cadmium(II) and
mercury(II) were found. Solutions of IAs are aggregatively stable at metal ion
concentrations less than 10
-6
mol L
-1
. It is shown in the Fig. 8 that increase in the Bi(III)
concentration is accompanied with increasing the intensity of the band at 610 nm
corresponding to the aggregated Astra Phloxine ions. The sensitivity of the
spectrophotometric determination of bismuth (III) was 5×10
-8
mol L
-1
, and by method
of sequential injection analysis using an external reactor (SIA-Lab-on-valve) –
8×10
-8
mol L
-1
. The quantitative formation of IA was observed at KI concentration of
at least 5 ×10
-3
mol L
-1
and in the range of concentrations of hydrochloric acid from
0.07 M to 0.2 M. To guarantee the complete formation of IA, only a small excess of
1
2
3
4
5
6
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