A new application of atomic absorption spectrophotometry : Determination of phthalic acid by solvent extraction with neocuproine-copper(I) chelate

A new application of atomic absorption spectrophotometry is reported for the determination of phthalic acid. Phthalic acid is extracted as the ion-pair formed between bis(neocuproine)-copper(I) and the univalent anion of phthalic acid with MIBK; the copper concentration in the extract is then determined by atomic ab sorption in an air-acetylene flame at the 3247 Å copper line. Optimal conditions are described. The absorbance of the extract showed a linear relationship to the concentration of phthalic acid initially present in the aqueous solution over the range of 4·10^-6 to 4·10^-5M. The effect of some analogous aromatic carboxylic acids on the phthalate extraction and the composition of the extracted species were also investigated.     

The determination of thallium(III) with the 2,2'-bipyridyl-iron(II) chelate

A spectrophotometric determination of thallium (III), based on solvent extraction of an ion-association pair formed between the cationic 2,2'-bipyridyl-iron(II) chelate and the anionic thallium(III) bromide complex is described. The best extractant is 1,2-dichloroethane and extraction is possible over the pH range 2.5–6.7. The composition of the extracted species was confirmed, and conditions were established for the extraction over the concentration range 7.9·10^-6–3.5·10^-5M of thallium in aqueous solution.     

Extraction of Palladium(II) and Platinum(IV) from Hydrochloric Acid Solutions with Trioctylammonium Nitrate Ionic Liquid without Dilution

The fundamental properties and extraction capability of an ionic liquid (IL), trioctylammonium nitrate ([HTOA][NO₃]), for Pd^II and Pt^IV, are investigated. At room temperature, [HTOA][NO₃] is a solid (melting point: 30.7 °C), but it becomes a liquid (melting point: 16.7 °C) when saturated with water. Water-saturated [HTOA][NO₃] exhibits a viscosity of 267.1 mPa·s and an aqueous solubility of 2.821?×?10^?4 mol·dm^?3 at 25 °C, and can be used as an extraction solvent without dilution. [HTOA][NO₃] exhibits an extremely high extraction capability for Pd^II and Pt^IV in dilute hydrochloric acid (0.1–2 mol·dm^?3 HCl); the distribution ratio reaches 3 × 10⁴ for both the metals. From electrospray ionization mass spectrometry analysis, the species extracted in the IL phase are [PdCl₃]^? and [PdCl₂(NO₃)]^? for Pd^II and [PtCl₆]^2? and [PtCl₅]^? for Pt^IV. A majority of the other transition metals are considerably less or marginally extracted into [HTOA][NO₃] from a 0.1 mol·dm^?3 hydrochloric acid solution. The extraction capacity of [HTOA][NO₃] is greater than that of other hydrophobic ILs such as [HTOA]Cl and bis(trifluoromethanesulfonyl)imide-based ILs. The metals extracted into the IL phase are quantitatively back-extracted using an aqueous solution containing thiourea and nitric acid. By controlling the thiourea concentration and shaking time, Pd^II and Pt^IV are mutually separated to some extent in the back extraction process. The IL phase used for the back extraction can be reused for the forward extraction of these metals after scrubbing it with an aqueous nitric acid solution.     

Extraction—spectrophotometric determination of traces of cadmium with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of cadmium is described. The ion-associate formed between the cadmium-PAR anionic chelate and cetyldimethylbenzylammonium chloride (CDBA) is extracted with chloroform at pH 10. The absorption maximum of the extracted species occurs at 505 nm, the molar absorptivity being (9.82 ± 0.30) × 10⁴ l mol^-1 cm^-1. The optimal concentration range for measurements is 0.2–1.0 μg Cd ml^-1; Beer's law is obeyed. The composition of the ion-associate is estimated to be CdPAR₂-2CDBA. The conditional extraction constant is log K'_ex ≈ 8. The stability constant of the cadmium—PAR chelate in aqueous solution is log β₂ = 17.5 ± 0.3. Extraction with N-benzoyl-N-phenylhydroxylamine is used to avoid several interferences. Moderate amounts of zinc are masked with sodium hydroxide.     

Extraction of metals by bis-(2-ethylhexyl) phosphoric acid in 2-ethylhexanoic acid as monomerizing diluent from an aqueous chloride phase: Am(III), Eu(III), Tm(III) and Y(III)

The extraction of Am³⁺, Eu³⁺, Tm³⁺ and Y³⁺ from an aqueous chloride phase into a solution of bis 2-ethylhexyl phosphoric acid, (2-C₂H₅·C₆H₁₂O)₂PO(OH), HDEHP, in the monomerizing diluent 2-ethylhexanoic acid has been studied in terms of the concentration of hydrogen ion in the equilibrated aqueous phase and of HDEHP in the opposing equilibrated organic phase. The extraction stoichiometries, with the corresponding expression for K in terms of F (the formality of HDEHP in the organic phase), [H⁺](the concentration of hydrogen ion in the aqueous phase), and K_S, for a 1.00 F(NaCl + HCl) aqueous phase are

where HY represents the monomer of HDEHP and the formulations of extracted species are non-committal with respect to structure. With HZ representing the monomer of 2-ethylhexanoic acid, suggested formulations of the extracted species in terms of homogeneousand heterogeneous dimers are: for Am³⁺, and Eu³⁺, M(HYZ)₃; and for Tm³⁺, Y³⁺, M(HY₂)₂(HYZ). The K_S values are: Am³⁺(5 × 10⁻³), Eu³⁺(1 × 10⁻²), (1 × 10⁻²), Tm³⁺(7) and Y³⁺(2).     

Analytical applications of picolinealdehyde salicyloylhydrazone: II. Extraction and spectrophotometric determination of vanadium(V)

Picolinealdehyde salicyloylhydrazone reacts with vanadium(V) to produce a yellow 1:1 complex (λ_max = 400 nm, ? = 2.17 × 10⁴ liters · mol^?1 cm^?1) in aqueous ethanolic solution. The yellow complex can be extracted into chlorobenzene (λ_max = 425 nm, ? = 2.16 × 10⁴ liters · mol^?1 cm^?1) and used for the spectrophotometric determination of trace amounts of vanadium. Interferences have been investigated. The method has been applied to the determination of vanadium in steel and in lead concentrates.     

Nickel(II) complexes based on products of condensation of aroyl(perfluoroacyl)methanes with benzoylhydrazine

A series of novel complexes NiL ⁿ · NH₃ were obtained by reactions of equimolar amounts of the ligands H₂L ⁿ (prepared by condensation of aroyl(perfluoroacyl)methanes with benzoylhydrazine) as solutions in ethanol and nickel(II) acetate as a solution in aqueous ammonia. The empirical formulas and square planar structures of the complexes obtained were determined using elemental analysis, IR and ¹H NMR spectroscopy, and X-ray diffraction.     

Extraction-spectrophotometric determination of palladium with triphenylphosphine (TPP)

Palladium is extracted with triphenylphosphine (TPP) solution in benzene from hydrochloric acid medium as the PdCl₂ · 2TPP complex showing maximum absorption at 346 nm and a molar absorptivity of ? = 2.26 × 10⁴.The conditions of palladium extraction have been examined and the composition of the extracted species has been found to be PdCl₂ · 2TPP.A 20-fold excess of other platinum and transition metals has no effect on the palladium extraction. Palladium can be determined at platinum concentrations up to 5 mg/ml provided that the result is corrected for the blank. The elaborated method has been applied to the analysis of platinum samples containing not less than 10^?3% of palladium.     

Kinetics of the photoaquation of Hexacyanoferrate(II) ion

Kinetics of the photoaquation of hexacyanoferrate(II) ion in aqueous solution were studied potentiometrically and spectrophotometrically. Supposing the simplest mechanism (see Fig. 3. in text), the photoaquation in alkaline medium can be well described. The value of the constants at pH = ll.0 are: ø = 0.8-1.0, k₆ = (3.0 ± 0.5) × 10^?8 s^?1 and k_?6 = 1.5 ± 0.2 mol^?1 dm₃ s^?1. To describe the photoaquation in neutral medium t was extended (k′ = 3.33 x 10² mol^?1 dm³s^?1). The quantum yield in acidic medium can be calculated by combination of ø values of different protonated complexes. The reversibility of photoaquation in alkaline medium is also explained by the scheme.     

Extraction—spectrophotometric determination of boron with 2,6-dihydroxybenzoic acid and 4-(4-diethyl-aminophenylazo)-n-methylpyridinium iodide,with application to steels

The sensitive and selective method reported is based on the reaction of boric acid with 2,6-dihydroxybenzoic acid in acidic aqueous solution to form a 1:2 complex anion which can be extracted into chloroform as an ion-pair with 4-(4-diethylaminophenylazo)-N-methylpyridinium ion. The ion-pair formed by the excess of reagents and co-extracted into chloroform, is removed by washing the organic phase with phosphate buffer solution (pH 7.0) and 0.025 M sulfuric acid solution. The absorbance of azo dye in chloroform is measured at 570 nm. Calibration graphs are linear in the range 0–1.5 × 10^-5 M of boron. The molar absorptivity is 6.6 × 10⁴ l mol^-1 cm^-1 and the absorbance of the reagent blank is 0.030. The method was applied to the determination of boron at the 0.001% level in steels.     

“Palladiazo” a new selective metallochromic reagent for palladium: Part I the main characteristics of the pure reagent and its reaction with palladium(II)

The synthesis and purification of 2,7-bis(4-azophenylarsono)-1,8-dihydroxy-naphthalene 3,6-disulphonic acid is reported. Because of its selectivity for palladium-(II), the name palladiazo is suggested for the reagent. Aqueous solutions of palladiazo are very stable and exhibit 2 absorption maxima located at 540 and 625 nm, the molar absorptivities being 3.3 · 10⁴ and 1.7 · 10⁴, respectively. Palladiazo changes color stepwise and reversibly with increase in hydrochloric acid concentration from 0 to 13 M. A negatively charged complex of type M₂L₃ is formed with Pd(II) at pH 2.5–3.5, and shows an absorption maximum at 640 nm with a molar absorptivity of (5.7 ± 0.1) ·10⁴; the complex can be readily extracted with diphenylguanidine chloride or quaternary ammonium salts dissolved in n-butanol or higher alcohols. The complex obeys Beer's law at 675 nm in the concentration range 10–250 μg Pd(II)/50 ml. Pb(II), Bi(III), Ce(III) and the rare-earth elements are the only expected cationic interferences.     

Kinetic determination of ascorbic acid by the 2,6-dichlorophenolindophenol reaction with a stopped-flow technique.

The reaction of ascorbic acid with 2.6-dichlorophenolindophenol is applied for the kinetic determination of ascorbic acid in 0.05M oxalic acid. Stopped-flow techniques are used; the concentrations of the reactants of the second-order reaction can be adjusted so that the transmittance signal remains nearly invariant for a wide range of voltage. Theoretical and experimental results are in very good agreement. Analytical working curves are presented for the determination of ascorbic acid in the ranges 5.0·10^-4–1.0·10^-2M and 5.0·10^-5–1.0-·10^-3M with errors of 1.0% and 2.2%. respectively. The method is simple, fast and sensitive.     

Synthesis, crystal structure, and structural features of hexa(isothiocyanate)chromates(III) of lanthanum(III) and neodymium(III) complexes with nicotinic acid

[M(C₅H₅NCOO)₃(H₂O)₂][Cr(NCS)₆] · nH₂O complexes, where M = La and n = 2 (1) or M = Nd and n = 1 (2), were synthesized by reacting M(NO₃)₃ (M = La, Nd, K₃[Cr(NCS)₆]) and nicotinic acid (C₅H₅NCOO) in aqueous solution. Their structure was established by IR spectroscopy and X-ray diffraction analysis. The crystals of complexes 1 and 2 are monoclinic, space group P2₁/n, Z = 2; for complex 1, a = 9.66800(10) Å, b = 25.7662(2) Å, c = 15.4843(2) Å, β = 106.4700(10)sO, V = 3698.99(7) ų, ρ_calcd = 1.761 g/cm³; for complex 2, a = 9.53120(10) Å, b = 25.5166(4) Å, c = 15.3843(3) Å, β = 104.9450(10)sO, V = 3614.96(10) ų, ρ_calcd = 1.779 g/cm³. Different hydrate compositions of the given compounds may be due to the specific features of intermolecular interactions in their structures.     

Catalytic determination of ultratrace amounts of selenium(iv)

A new sensitive catalytic method for determining selenium(IV) is proposed. Selenium catalyzes the oxidation of p-hydrazinobenzenesulfonic acid to p-diazobenzenediazonium ion, which then is converted to a yellow azo dye by coupling with m-phenylenediamine. As little as 10^-7 M selenium(IV) can be determined easily; the effective molar absorptivity is 1.2 · 10⁶ for selenium(IV). If the azo dye is extracted into an organic solvent, the effective molar absorptivity can be increased further to 2.4· 10⁶ for selenium(IV).     

Stability constants of iron(III)-8-hydroxyquinoline complexes

Spectrophotometric determination of the formation constants of iron(III)-8-hydroxyquinoline complexes in 0.1 M sodium perchlorate solution at 25° gave the values K₁=[FeOx²⁺]/([Fe³⁺][Ox^-])=4.9·10¹³, K₂=[FeOx₂⁺]/([FeOx²⁺][Ox^-])=4.2·10¹² and K₃=[FeOx₃]/([FeOx₂⁺][Ox^-])=3.9·10¹⁰. FeOx₂OH and FeOx(OH)₂ are obtainable as solid phases. FeOx₃ (K_sp=3·10^-44, intrinsic solubility 1.6·10^-7 M) dissolves in basic solutions to form FeOx₂(OH)₂ -In a solution saturated with FeOx³, ([FeOx₂(OH)₂^-][Ox^-])/[OH^-]²=7.7·10^-5.     

Crystal structure of 1-cyclohexylpiperazine-1,4-diium dichromate(VI)

Single crystals of 1-cyclohexylpiperazine-1,4-diium dichromate(VI), (C₁₀H₂₂N₂)[Cr₂O₇], were obtained by slow evaporation at room temperature from an aqueous solution of potassium dichromate, hydrochloric acid and 1-cyclohexylpiperazine. (C₁₀H₂₂N₂)[Cr₂O₇] is triclinic (P\(\bar 1\)) with a = 10.351(2) Å, b = 12.766(3) Å, c = 6.111(1) Å, α = 91.50(2)°, β = 104.26(3)°, γ = 94.91(2)°, V = 778.8(3) ų, and Z = 2. The structure determination performed from single crystal X-ray diffraction data leads to R₁/wR₂ reliability factors of 0.032/0.078. The asymmetric unit of the title salt C₁₀H₂₂N₂²⁺·Cr₂O₇^2?, consists of one 1-cyclohexylpiperazine-1,4-diium dication and one dichromate dianion. These entities are linked together by N–H···O hydrogen bonds to form {(C₁₀H₂₂N₂)[Cr₂O₇]}_n infinite chains lying parallel to the (100) plane and running along the c axis. The intermolecular N–H···O hydrogen bonds link these chains into a two-dimensional network structure consolidated through C–H···O weak interactions.     

The electrocatalytic reduction of carbon dioxide using cobalt tetrakis (4-trimethylammoniophenyl) porphyrin under high pressure

The electrocatalytic reduction of carbon dioxide in aqueous solution using Co [p-N(CH₃)₃) TPPI under pressure (4～22 kg · cm^?2) was carried out on solid-state metal electrodes such as In, Sn, Pb and Pb-Hg. The reduction products were mainly carbon monoxide and a small amounts of formic acid. The effects of the pressure of carbon dioxide, electrolytes, catalyst concentration, electrode materials and potentials on the reduction of carbon dioxide were studied. The optimum voltage for maximum current efficiency of reduction products was at ?1.2 Vvs. SCE for all four kinds of metal electrodes. High current efficiencies (>90%) were obtained with lead and amalgamated lead electrodes in an aqueous solution of NaHCO₃ containing 7.4 × 10×⁵ mol/L of catalyst.     

Potentiometric and Theoretical Studies of (2Z, 3Z)-2H-benzo[b][1,4]thiazine-2,3(4H)-dionedioxime with Some Divalent Transition Metal Ions

The protonation equilibria of (2Z, 3Z)-2H-benzo[b][1,4]thiazine-2,3(4H)-dionedioxime (BTDH₂) together with the equilibria of its bis- binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) were investigated potentiometrically. The investigation was carried out at 25 ± 0.1 °C, in aqueous solution, with a constant ionic strength of 0.100 mol·dm^?3 NaCl. The protonation constants of the ligand together with the stability constants of a variety of complexes were determined potentiometrically in 10 % ethanol–water mixed solution using the SUPERQUAD computer program. Theoretical calculations were set up to assist in understanding the protonation sequence in the ligand molecule via the semi-empirical molecule orbital method of parameterized model number 3. Results are discussed in connection to the basicity of the donor atoms and structural arrangement of the ligand. Although BTDH₂ has two dissociable protons, four protonation constants can be measured under the experimental conditions presented. These four protonation constants (as log₁₀ βs) are 10.245, 19.397, 22.414 and 25.176.     

Binuclear chelates of diethylenetriamine-Pentaacetic acid with chromium(III) and oxovanadium(IV) ions

The reactions of diethylenetriaminepentaacetic acid (DTPA=H₅L) or chromium(III)-DTPA, a ‘chelating agent’, with oxovanadium(IV) were investigated in aqueous solution by potentiometric methods. Homo- and hetero-binuclear species were evidenced as well as mixed complexes with hydrogen or hydroxide ions. The stability constants for these equilibria were calculated in 1.0 mol 1^?1 NaClO₄ solution at 20?C. The mononuclear (VO)H₃L·H₂O and the heterobinuclear (VO)CrL·5H₂O complexes were also obtained as solid compounds and were characterized by IR spectroscopy and thermoanalytical techniques (TG and DSC).     

Extraction-photometric determination of uranium(IV) with chlorophosphonazo-III

A sensitive spectrophotometric method has been developed for the determination of uranium. The uranium(IV)-chlorophosphonazo-III complex is extracted into 3-methyl-1-butanol from 1.5–3.0 M hydrochloric acid solution. Maximal absorbance occurs at 673 nm and Beer's law is obeyed over the range of 0–15 μg per 10 ml of the organic phase. The molar absorptivity is 12.1·10⁴ 1 mole^?1 cm^?1. Uranium can be determined in the presence of fluoride. sulfate and phosphate. Nitrate ion and elements (chromium, copper, iron) which affect the reduction of uranium(VI) or stability of uranium(IV) interfere.