The complexation reactions between 4-(2-pyridylazo)resorcinol (PAR) and Al 3+ , Fe 3+ , Zn 2+ , and Cd 2+ ions at 25 °C and 0.1 M ionic strength are performed spectrophotometrically. A critical comparison of the various PCA methods on the absorbance matrix data concerning the number of light-absorbing species has been made. Knowing the number of light-absorbing species is a critical step for subsequent quantitative and qualitative solution equilibria studies. Therefore, the nine selected index functions for the prediction of the number of light-absorbing components which contribute to a set of spectra are critically tested using the algorithms implemented in INDICES software. Behind the number of various complexes formed the stability constants of species ML and MLH, type log β 110 and log β 111 , for the system of PAR (ligand L) with Zn 2+ and Cd 2+ ions and the stability constants of species MLH and ML 2 H, type log β 111 and log β 121 , for the system of PAR (ligand L) with Al 3+ and Fe 3+ ions at 25 °C and 0.1 M ionic strength, and various mole ratios are estimated by the SQUAD and EQUISPEC programs.
Dissociation equilibria of 4-(2-pyridylazo) resorcinol (PAR) in aqueous micellar solutions were determined spectrophotometrically at 25°C and at the constant ionic strength I = 0.1 M KNO 3 . For this purpose, the effect of nonionic (Brij-35, Triton X-100, Triton X-114, Triton X-405), and anionic (SDS) surfactants on the absorption spectra of PAR at different pH values was studied. Results show that the pK a values and pure spectra of each species of PAR are influenced by percentages of a neutral and an anionic surfactant such as Brij-35, Triton X-100, Triton X-114, Triton X-405 and SDS, respectively, added to the solution of this reagent. Ghasemi et al. Fig. 3. The pure spectra of different forms of PAR in (a) pure water, (b) 0.05% (w/v) Brij-35 to water, (c) 0.05% (w/v) Triton X-100 to water, (d) 0.05% (w/v) Triton X-114 to water, (e) 0.05% (w/v) Triton X-405 to water and (f) 0.05% (w/v) SDS to water.
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