In the current study, the peculiarities of the complexation of Bi(III) with 6,7-dihyroxy‑4-carboxyl‑2-phenylbenzopyrylium perchlorate (CDC) in binary systems and in the presence of cationic surfactants (Surf) were studied. Using classical spectrophotometric methods of molar ratios and equilibrium shift, it was found that in two systems two complexes with stoichiometry Bi(III): CDC are formed: 1:2 and 1:3 at pH 2.0 and pH 4.5, respectively. Molar light absorption coefficients were calculated for Bi(III) complexes with CDC, which are 1.4⸱104 and 1.0⸱104, respectively. It is shown that in the presence of cetylpyridinium chloride or cetyltrimetrylammonium bromide complexes with a molar ratio of Bi(III): CDC: Surf =1:3:3 are formed. In the presence of cationic surfactants there is no shift in the optimal pH of complexation, but there is an increase in the number of coordinated reagent molecules due to the loosening of the hydrate shell of the ion Bi(III) due to hydrophobic hydration of the complex. In addition, the introduction of cationic surfactants leads to a batochromic shift of the absorption band by 10–15 nm and an increase in the molar absorption coefficient to 3.1⸱104 and 4.1⸱104 when using cetylpyridinium chloride or cetyltrimetrylammonium bromide, respectively. Methods of spectrophotometric determination of Bi(III) with the use of analytical forms based on complexes of 1:2 and ternary complex 1:3:3 were developed, which were tested in the analysis of pharmaceuticals, alloys and model solutions. It is noted that the proposed methods are characterized by satisfactory reproducibility and are not inferior in sensitivity to known analogues.

In the current study, the peculiarities of the complexation of Stibium(III) with 6,7-dihydroxy‑4-carboxyl‑2-phenylbenzopyrylium perchlorate (CDC) in binary systems and in the presence of cationic surfactants (Surf) were studied. Using classical spectrophotometric methods of molar ratios and equilibrium shift, it was found that in two systems two complexes with stoichiometry Sb(III): CDC are formed: 1:2 and 1:3 at pH 2.5 and pH 6.0, respectively. Molar absorptivity coefficients were calculated for Sb(III) complexes with CDC, which are 1.2⋅104 and 1.1⋅104, respectively. It is shown that in the presence of cetylpyridinium chloride or cetyltrimetrylammonium bromide complexes with a molar ratio of Sb(III): CDC: Surf =1:3:3 are formed. In the presence of cationic surfactants there is no shift in the optimal pH of complexation, but there is an increase in the number of coordinated reagent molecules due to the loosening of the hydrate shell of the ion Sb(III) due to hydrophobic hydration of the complex. In addition, the introduction of cationic surfactants leads to a batochromic shift of the absorption band by 10–15 nm and an increase in the molar absorptivity to 2.8⋅104 and 3.4⋅104 when cetylpyridinium chloride or cetyltrimetrylammonium bromide were used respectively. The method of spectrophotometric determination of Stibium(III) was developed using an analytical form based on the ternary complex Sb(III): KDC: Surf = 1:3:3, which was tested during the analysis of samples of polymer materials (polyethylene terephthalate). It is noted that the developed technique is characterized by satisfactory reproducibility and is not inferior in sensitivity to known analogues.