Vanadium-Containing Anionic Chelate for Spectrophotometric Determination of Hydroxyzine Hydrochloride in Pharmaceuticals.

Four azo dyes known to form anionic complexes with V(V) were investigated as potential liquid-liquid extraction-spectrophotometric reagents for the antihistamine medication hydroxyzine hydrochloride (HZH). A stable ion-association complex suitable for analytical purposes was obtained with 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR). The molar absorption coefficient, limit of detection, linear working range, and relative standard deviation in the analysis of real pharmaceutical samples (tablets and syrup) were 3.50 × 104 L mol-1 cm-1, 0.13 µg mL-1, 0.43-12.2 µg mL-1, and ≤2.7%, respectively. After elucidating the molar ratio in the extracted ion-association complex (HZH:V = 1:1), the ground-state equilibrium geometries of the two constituent ions-HZH+ and [VO2(HTAR)]--were optimized at the B3LYP level of theory using 6-311++G** basis functions. The cation and anion were then paired in four different ways to find the most likely structure of the extracted species. In the lowest-energy structure, the VO2 group interacts predominantly with the heterochain of the cation. A hydrogen bond is present (V-O···H-O; 1.714 Å) involving the terminal oxygen of this chain.

Use of a Hydrophobic Azo Dye for the Centrifuge-Less Cloud Point Extraction-Spectrophotometric Determination of Cobalt.

The hydrophobic azo dye 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR, H2L) was studied as part of a system for the centrifuge-less cloud point extraction (CL-CPE) and spectrophotometric determination of traces of cobalt. The extracted 1:2 (Co:HTAR) complex, [CoIII(HL-)(L2-)]0, shows an absorption maximum at 553 nm and contains HTAR in two different acid-base forms. Optimum conditions for its formation and CL-CPE were found as follows: 1 × 10-5 mol L-1 of HTAR, 1.64% of Triton X-114, pH of 7.8, incubation time of 20 min at ca. 50 °C, and cooling time of 30 min at ca. -20 °C. The linear range, limit of detection, and apparent molar absorptivity coefficient were 5.4-189 ng mL-1, 1.64 ng mL-1, and 2.63 × 105 L mol-1 cm-1, respectively. The developed procedure does not use any organic solvents and can be described as simple, cheap, sensitive, convenient, and environmentally friendly. It was successfully applied to the analysis of artificial mixtures and real samples, such as steel, dental alloy, rainwater, ampoules of vitamin B12, and saline solution for intravenous infusion.

Extraction System for the Spectrophotometric Determination of Tungsten(VI) with 4-Nitrocatechol and Benzalkonium Chloride.

A novel chromogenic system for the liquid-liquid extraction and determination of trace amounts of tungsten(VI) was investigated. The system comprises 4-nitrocatechol (4NC) as a chromogenic reagent, sulfuric acid as a complexing medium, and benzalkonium chloride (BAC) as a source of bulky cations (BA+), which readily form chloroform-extractable ion-association complexes. The impact of foreign ions and reagents was studied, and the optimal conditions for the sensitive, selective, and inexpensive determination of tungsten(VI) were identified. The limit of detection, linear working range, and molar absorptivity at lmax (422 nm) were determined to be 31 ng cm-3, 0.1-4.4 µg cm-3, and 5.49 × 104 dm3 mol-1 cm-1, respectively. The composition of the extracted complex was 1:2:2 (W:4NC:BA). Two potential structures of its anionic component, [WO2(4NC)2]2-, were discussed based on optimizations at the B3LYP/CEP-4G theoretical level and comparison between theoretical and experimental spectra.

Extraction-Chromogenic System for Cobalt Based on 5-Methyl-4-(2-thiazolylazo) Resorcinol and Benzalkonium Chloride.

The interaction between CoII and 5-methyl-4-(2-thiazolylazo)-resorcinol (MTAR) was studied in a water-chloroform system, in the presence or absence of benzalkonium chloride (BZC) as a cationic ion-association reagent. The optimum pH, concentration of the reagents and extraction time for the extraction of Co were found. In the presence of BZC, the extracted ion-associate could be represented by the formula (BZ+)[CoIII(MTAR2-)2], where MTAR is in its deprotonated form. The following extraction-spectrophotometric characteristics were determined: absorption maximum, molar absorptivity, Sandell's sensitivity, limit of detection, limit of quantification, constant of extraction, distribution ratio and fraction extracted. In the absence of BZC, the extraction is incomplete and occurs in a narrow pH range. The extracted chelate contains one deprotonated and one monoprotonated ligand: [CoIII(MTAR2-)(HMTAR-)].

Extraction-Chromogenic System for Nickel(II) Based on 5-methyl-4-(2-thiazolylazo)resorcinol and Aliquat 336.

A water-isobutanol extraction-chromogenic system for NiII, based on the azo dye 5-methyl-4-(2-thiazolylazo)resorcinol (MTAR; H2L) and the ionic liquid Aliquat 336 (A336), was studied. Under the optimal conditions (cMTAR = 2.0 × 10-4 mol dm-3, cA336 = 5.6 × 10-3 mol dm-3, pH 8.5 and extraction time t = 1 min), NiII is extracted as a ternary complex which can be represented by the formula (A336+)2[Ni(L2-)2]. In the absence of A336, or in a slightly acidic medium, a binary complex, [Ni(HL-)2], with an absorption maximum at l = 548 nm and a shoulder at 590 nm is formed. The following extraction-spectrophotometric characteristics were determined at the above-mentioned optimal conditions: lmax (545 nm), molar absorptivity (5.0 × 104 dm3 mol-1 cm-1), Sandell's sensitivity (1.2 × 10-3 ∆g cm-2), Beer's law limits (0.05-3.1 mg cm-3), constant of extraction (Log K = 6.1) and fraction extracted (99.2%). The effect of foreign ions was studied; the most serious interferences were caused by CoII, CuII and CrIII.

Extraction-Chromogenic Systems for Vanadium(V) Based on Azo Dyes and Xylometazoline Hydrochloride.

Liquid-liquid extraction-chromogenic systems for vanadium(V) based on xylometazoline hydrochloride (XMZ) and azo derivatives of resorcinol (ADRs) were studied. The following ADRs were used: 4-(2-thiazolylazo)resorcinol (TAR), 5-methyl-4-(2-thiazolylazo)resorcinol (MTAR), and 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR). Concentration of the reagents, pH of the aqueous medium and shaking time were subjects of optimization experiments. The chloroform-extracted ternary complexes were of composition 1:1:1. The molar absorptivity coefficients (el), absorption maxima (l), constants of extraction (Log K), and fractions extracted (E%) were found to be e553 = 2.50 ´ 104 dm3 mol-1 cm-1, Log K = 3.5, and E = 96% (ADR = TAR); e550 = 1.88 ´ 104 dm3 mol-1 cm-1, Log K = 3.4, and E = 98% (ADR = MTAR); and e554 = 2.62 ´ 104 dm3 mol-1 cm-1, Log K = 5.0, and E = 99.5% (ADR = HTAR). The Sandell's sensitivities and Beer's law limits were determined as well.

Liquid-Liquid Extraction-Chromogenic System for Vanadium(V) Based on 4-(2-thiazolylazo)orcinol (TAO) and Aliquat 336.

The quaternary ammonium salt Aliquat 336 (A336; R4N+Cl-) and the azo dye 4-(2-thiazolylazo)orcinol (ТАО) were examined as constituents of a water-isobutanol extraction-chromogenic system for vanadium(V). Under the optimum conditions (cTAO = 1.6´10-3 mol dm-3, cA336 = 1.3´10-2 mol dm-3 and pH 5.0), vanadium(V) is extracted as a ternary complex which can be represented by the formula (R4N+)[VO2(TAO2-)]. The key extraction-spectrophotometric characteristics were determined. The interfering effect of foreign ions was studied as well. The wavelength of maximum absorption (λmax), molar absorptivity (εmax), constant of extraction (Kex) and fraction extracted (E) were found to be λ = 547 nm, ε = 3.1×104 dm3 mol-1 cm-1, Log Kex = 2.8 and E = 90.2%, respectively. Beer's law was obeyed in the range of 0.084-2.0 mg cm-3 and the limit of detection was 25 ng cm-3 of vanadium(V).

A 2:2:2 Complex of Vanadium(V) with 4-(2-Thiazolylazo)orcinol and 2,3,5-Triphenyl-2H-Tetrazolium Chloride.

The complex formation in the vanadium(V)/4-(2-thiazolylazo)orcinol (TAO)/2,3,5-triphenyl-2H-tetrazolium chloride (TTC) liquid-liquid extraction-chromogenic system was studied. The chloroform-extracted complex has a composition of 2:2:2 under the optimum conditions (pH 4.8-5.2, extraction time 3 min, concentration of TAO 3.4 × 10(-4) mol dm(-3), and concentration of TTC 9.4 × 10(-4) mol dm(-3)) and could be regarded as a dimer (D) of two 1:1:1 species (S) presented by the formula (TT+)[VO2(TAO)]. The constant of extraction was calculated by two methods and some analytical characteristics were determined. The wavelength of maximum absorption (λmax), molar absorptivity (ελ) and fraction extracted (E) were found to be λ = 545 nm, ε545 = 1.97 × 10(4) dm(3) mol(-1) cm(-1), and E = 97.9%. The ground-state equilibrium geometries of the complexes S and D were optimized by quantum chemical Hartree-Fock calculations using 3-21G* basis functions. The bonding and interaction energies were calculated as well.