Extraction-Spectrophotometric Studies on the Ion-Pairing Between Some 2,3,5-Substituted Monotetrazolium Cations and Anions Deriving from 4-(2-Thiazolylazo)resorcinol or 4-(2-Pyridylazo)resorcinol

The ion-pairing between some 2,3,5-substituted monotetrazolium cations (T+) and anions deriving from 4-(2-pyridylazo)resorcinol (PAR) or 4-(2-thiazolylazo)resorcinol (TAR) was studied by water-chloroform extraction and spectrophotometry. The following tetrazolium salts (TS) were used as a source of T+: i) 2,3,5-triphenyl-2H-tetrazolium chloride (TTC); ii) 3-(4,5-dimethyl-2-thiazol)-2,5-diphenyl-2H-tetrazolium bromide (MTT); iii) 3-(2-naphtyl)-2,5-diphenyl-2H-tetrazolium chloride (Tetrazolium violet, TV); and iv) 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT). The spectral characteristics of the extracted species were established at different pH and TS concentration. The composition and stability of the ion-pairs were determined at pH 9, where the extraction of neutral PAR (H2PAR) and TAR (H2TAR) species was negligible. The results showed that the ion-pairs can be expressed with the following formulae (T+)(HTAR–) (where T+ = TT+, MTT+, TV+ or INT+), (T+)(HPAR–) (where T+ = TT+, MTT+ or TV+) and [(INT+)(HPAR–)]2. Relationships involving the molecular masses of the ion-pairs (MIP) or T+ (MT+) and the values of the constants of association (b) or conditional molar absorptivities (e’) were examined, namely Log b = f(Log MIP) and e’ = f(Log MT+). Some practical aspects concerning the investigation of metal complexes with TS-PAR/TS-TAR were discussed

An extraction-chromogenic system for vanadium(IV,V) based on 2,3-dihydroxynaphtahlene

A liquid-liquid extraction-chromogenic system for vanadium(IV, V) containing 2,3-dihydroxynaphtahlene (DN), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), water and chloroform was studied in detail. When the vanadium is in the oxidation state of IV, the extracted species are aggregates containing three 1:2:1 (V:DN:TTC) ion-pair units composed of triphenyltetrazolium cations (TT+) and chelate anions {[VIVO(DN)(DNH)]− (I) and/or [VIV(OH)(DN)2]− (II)}. When the initial oxidation state of vanadium is V and the DN concentration is high, vanadium(V) is reduced by DN to a lower oxidation state, V(IV). However, at low DN concentration, vanadium(V) can enter the organic phase as a part of an ion-pair consisting of TT+ and [VVO2(DN)]− (III). The ground-state equilibrium geometries of the anions I, II, and III were optimized by quantum chemical calculations using BLYP/6-31++G⋆. The following characteristics were determined under the optimum conditions for VIV extraction: absorption maximum λmax = 333 nm, molar absorptivity ε333= 2.1x104 dm3 mol−1 cm−1, Sandell’s sensitivity SS = 2.4 ng cm−2, and fraction extracted E = 98%. The conditional extraction constant was calculated by two independent methods. The calibration graph was linear in the range 0.1-3.1 μg cm−3 (R2=0.9994) and the limit of detection was 0.03 μg cm−3

Extractive Spectrophotometric Determination and Theoretical Investigations of Two New Vanadium(V) Complexes

Two new vanadium (V) complexes involving 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR) and tetrazolium cation were studied. The following commercially available tetrazolium salts were used as the cation source: tetrazolium red (2,3,5-triphenyltetrazol-2-ium;chloride, TTC) and neotetrazolium chloride (2-[4-[4-(3,5-diphenyltetrazol-2-ium-2-yl)phenyl]phenyl]-3,5-diphenyltetrazol-2-ium;dichloride, NTC). The cations (abbreviated as TT+ and NTC+) impart high hydrophobicity to the ternary complexes, allowing vanadium to be easily extracted and preconcentrated in one step. The complexes have different stoichiometry. The V(V)–HTAR–TTC complex dimerizes in the organic phase (chloroform) and can be represented by the formula [(TT+)[VO2(HTAR)]]2. The other complex is monomeric (NTC+)[VO2(HTAR)]. The cation has a +1 charge because one of the two chloride ions remains undissociated: NTC+ = (NT2+Cl−)+. The ground-state equilibrium geometries of the constituent cations and final complexes were optimized at the B3LYP and HF levels of theory. The dimer [(TT+)[VO2(HTAR)]]2 is more suitable for practical applications due to its better extraction characteristics and wider pH interval of formation and extraction. It was used for cheap and reliable extraction–spectrophotometric determination of V(V) traces in real samples. The absorption maximum, molar absorptivity coefficient, limit of detection, and linear working range were 549 nm, 5.2 × 104 L mol−1 cm−1, 4.6 ng mL−1, and 0.015–2.0 μg mL−1, respectively