The structure of styryl dye, 2-[(E)-2-(4-dipropylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3H-indolium chloride (I), was investigated using methods such as UV-VIS, fluorescence spectroscopy, and NMR (1H, 13C, APT, HMQC, COSY) and also by examining its electrochemical properties. A study of the acid-base properties revealed the existence of three different forms of the dye. The mechanisms of protolysis and hydrolysis are discussed. The reagent exists in a reactive single-charged form I + over a wide range of acidity (pH 4–11). The optimum analytical wavelength of the singlecharged form is 550 nm, where the molar absorptivity is 5.51 × 104 L mol−1 cm−1. The values of the optimum analytical wavelength and molar absorptivity of the protolysed and hydrolysed forms are: λ max(I-H2+) = 380 nm, ɛ(I-H2+) = 2.01 × 104 L mol−1 cm−1; λ max(I-OH) = 320 nm, ɛ(I-OH) = 1.12 × 104 L mol−1 cm−1. A theoretical study of the spectral and chemical properties of I was carried out by performing quantum chemical calculations.

A new, simple, rapid, sensitive, efficient and low-cost spectrophotometric procedure for the determination of gold was developed. The method is based on the reaction of [AuCl4](-) with 2-[2-(4-dimethylaminophenyl)-vinyl]-1,3,3-trimethyl-3H-indolium reagent to form a colored ion associate extractable by various organic solvents. The molar absorptivity of the ion associates is in the range (5.7-9.2) x 10(4) L mol(-1) cm(-1) depending on the extractant. Butyl acetate was chosen as the extractant. The optimum reaction conditions were established: pH 2-4, concentration of the dye reagent (0.8-1.5) x 10(-4) mol L-1. The determination of gold is not hindered even by a 1000-fold concentration of Ni and Co; a 500-fold concentration of Pb and Zn; a 100-fold concentration of Bi, Cu, Cd, Pt, Rh and Ru; or a 20-fold concentration of Ag. The established method was applied to the determination of gold in model samples and enriched polymetallic ores.

The acid- base properties of 2-[2-(4-methoxy-phenylamino)-vinyl]-1,3,3-trimethyl-3H-indolium dye were investigated. The reagent exists in a reactive single charged form over a wide range of acidity, from pH 8 to -2.5 H-0. The optimum analytical wavelength of the single charged form is 412 nm, where the molar absorptivity is 4.06 x 10(4) dm(3) mol(-1) cm(-1). Mechanisms of protonation and hydrolysis were discussed. The results suggest the applicability of the dye as an effective analytical reactant. Quantum chemical calculations of the structural and spectral properties of the dye were also carried out.

A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of nitrophenols [picric acid (PA); dinitrophenols (DNP)] in wastewater samples. The method is based on the reaction of nitrophenols with 2-[( E )-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3 H -indolium chloride reagent to form the colored ion associates, which are extracted by organic solvents. The molar absorptivity of the ion associates of PA with the investigated reagent ranges from 8.3×10 4 to 11.3×10 4 L mol −1 cm −1 , depending on the extractant. Because only PA is extracted in an acidic medium with the investigated reagent, but both PA and DNP are extracted in an alkaline medium, it is possible to determine both substances in a mixture. Appropriate reaction conditions have been established. The absorbance of the colored extracts obeys Beer’s law in the range of 0.04–4.58 mg L −1 PA, 1.0–18.4 mg L −1 2,4-DNP and 1.2–14.7 mg L −1 2,6-DNP, respectively. The limit of detections, calculated from a blank test ( n =10; P =0.95), are 0.05 mg L −1 PA, 0.9 mg L −1 (2,4-DNP), and 1.1 mg L −1 (2,6-DNP), respectively.