Investigation of polynuclear Zr(IV) hydroxide complexes by nanoelectrospray mass-spectrometry combined with XAFS

Polynuclear species of zirconium in acidic aqueous solution are investigated by combining X-ray absorption spectroscopy (XAFS) and nanoelectrospray mass spectrometry (ESI-MS). Species distributions are measured between pH_C 0 and pH_C 3 for [Zr] = 1.5–10 mM. While the monomer remains a minor species, with increasing pH the degree of polymerization increases and the formation of tetramers, pentamers, octamers, and larger polymers is observed. The high resolution of the mass spectrometer permits the unambiguous determination of polynuclear zirconium hydroxide complexes by means of their isotopic patterns. The relative abundances of mononuclear and polynuclear species present simultaneously in solution are measured, even if one of the species contributes only 0.1% of the Zr concentration. For the first time it has been directly observed that the hydrolysis of polynuclear Zr species is a continuous process which leads to charge compensation through the sequential substitution of water molecules by hydroxide ligands until doubly charged polymers dominate at conditions (H⁺ and Zr concentrations) close to the solubility of Zr(OH)₄(am). The invasiveness of the electrospray process was minimized by using very mild declustering conditions, leaving the polynuclear species within a solvent shell of approximately 20 water molecules. Figure Schematic Diagram of Multiplexed Measurement of 9 Anti-Nuclear Antibodies Using the AtheNa Multilyte Assay     

Free-radical intermediates in hydrogenation of celoro-substituted nitrobenzenes in presence of Ir(IV) complex with chloranilic acid

Conclusions When 3,4-dichloronitrobenzene is hydrogenated in the presence of the Ir complex with chloranilic acid, the intermediates have a radical nature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 463–464, February, 1982.     

Atomic-absorption spectrometric determination of calcium, magnesium and potassium in leaf samples after decomposition with molten sodium hydroxide

The decomposition of standard leaf samples of varied origin and nature by fusion with sodium hydroxide in an open system has been studied. The use of sodium nitrate as an auxiliary agent facilitated the mineralization of most of the samples. The solutions obtained were analysed for calcium, magnesium and potassium by flame atomic-absorption spectrometry. The method is fast and quite precise, with absolute standard deviations of 0.04-0.13, 0.002-0.03 and 0.04-0.12% for calcium, magnesium and potassium contents of O.8-5.0, 0.13-0.48 and 0.36-2.2% respectively. The limits of detection (mug/ml) in the determination step were 0.10 for calcium, 0.011 for magnesium, and 0.09 for potassium.     

Spectrophotometric determination of atropine, pilocarpine and strychnine with chloranilic acid

In dioxan-chloroform medium the acceptor chloranilic acid forms 1:1 molecular complexes with the alkaloids atropine, pilocarpine and strychnine, with maximum absorption at 535, 527.5 and 535 nm respectively. Conformity with Beer's law allows the use of the complexes for the assay of these drugs.     

Redox behaviors of zirconium in molten LiCl-KCl eutectic salt based on the comproportionation reaction between Zr(0) and Zr(IV)

The electrochemical behavior of Zr was investigated by a unique comproportionation reaction between Zr(0) and Zr(IV) in molten LiCl-KCl eutectic salt. Based on X-ray photoelectron spectroscopy and square wave voltammetry, the unknown Zr ion, which is the product of comproportionation reaction, was disclosed as Zr(III) instead of Zr(II). Additionally, the cyclic voltammogram of LiCl-KCl-ZrCl₄ system showed a significant difference by changing the working electrode. In accordance with the experimental results, the expected reaction for the major redox peaks on cyclic voltammogram was suggested in comparison with other literatures.     

Reversed phase HPLC determination of titanium(IV) and iron(III) with sodium 1,2-dihydroxybenzene-3,5-disulfonic acid

A highly sensitive method has been developed for the determination of titanium(IV) and iron(III) by ion-pair reversed phase liquid chromatography using sodium 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron) as a precolumn chelating reagent. The metal - Tiron chelates were separated on a C₁₈ (ODS) column; the mobile phase was a 2:8 (v/v) mixture of acetonitrile and acetate buffer (0.04 mol/L, pH 6.2) containing 2.0 × 10^?3 mol/L Tiron, 0.04 mol/L tetrabutylammonium bromide, and 0.1 mol/L potassium nitrate. The detection limits for titanium(IV) and iron(III) are 0.5 and 2.0 μg/L, respectively. The method has been applied to the simultaneous determination of titanium(IV) and iron(III) in river water samples and has furnished highly precise results.     

Spectrophotometric determination of vanadium(IV) with nitrilotriacetic acid

A new and convenient spectrophotometric method for the estimation of vanadium(IV) with NTA is described. The minimum ratio of metal ion to ligand, working pH, wavelength for maximum absorbance of the complex ion, and the effect of various cations and anions are described. The complex ion obeys Beer's law in the concentration range 1–32 mmol/liter of the vanadium(IV) ion. It is observed that iron(II), cobalt(II), nickel(II), copper(II), and oxidizing anions such as chromate and nitrite interfere in this determination, whereas managanese(II), chromium(III), iron(III), and anions like nitrate, chloride, bromide, iodide, thiocyanate, sulfate, and sulfite do not have any effect. Excessive amounts of acetate, phosphate, oxalate, tartrate and thiosulfate must also be avoided in this determination. Anions and cations which interfere in the determination of vanadium(IV) by NTA should not be present in the system.     

Zr(IV) and Hf(IV) based metal-organic frameworks with reo-topology

Zr and Hf based MOFs with enhanced pore accessibility for large molecules and good hydrothermal stability were obtained using a bent dithienothiophene dicarboxylate and Zr(4+) or Hf(4+) source. A modulator (benzoic acid) facilitates formation of an eight-connecting cluster leading to a new framework which adopts reo topology.     

Spectrophotometric determination of silicate in natural waters by formation of α-molybdosilicic acid and reduction with a tin(IV)-ascorbic acid-oxalic acid mixture

Reaction of dissolved silicate with molybdate at pH 3.8–4.8 in acetate buffer yields only the α-molybdosilicic acid. Treatment of this acid with a solution containing tin(IV) chloride, ascorbic acid and oxalic acid rapidly gives the blue reduced acid without reducing the excess of molybdate reagent. In the recommended procedure, Beer's Law is followed at 740 nm over the range 0–2000 μg Si l^-1 with a coefficient of variation of 0.34% at 400 μg Si l^-1 and 0.52% at 40 μg Si l^-1. The sensitivity of the method is not affected by ionic strength.     

Spectrophotometric determination of cerium(IV) with tetraethylenepentaamineheptaacetic acid (TPHA)

Tetraethylenepentaamineheptaacetic acid (TPHA) combines with cerium(IV) to form an intensely yellow chelate having a molar absorptivity of 4.5 × 10⁴ mol⁻¹ · cm⁻¹ · liter at 304 nm. The chelate contains 1 mol of TPHA coordinated to a cerium(IV) atom. Beer's law is followed from 0.05 to 0.5 ppm cerium (1.00-cm cells). Of many ions tested at the 1-ppm level and the 100-ppm concentration, only iron(III) produces little interference.     

Crystalline phase effects on esca valence bands of Zr(IV) and Ti(IV) acid phosphates

The valence bands (V.B.) of ESCA spectra of Zr(IV) and Ti(IV) acid phosphates in different crystalline phases are reported. The various bands are assigned by comparison with Li₃PO₄. Variations on changing the crystalline phase for compounds having the same M(IV) ion are found. Two types of molecular orbitals are mainly involved. One related to PO bonds is affected by the crystalline phase. The other, related to M(IV)O bonds and confined into the layers of the compounds, are less sensitive to crystalline environment. Variation in the symmetry of the tetrahedral type PO^3?₄ anion are proposed to be mainly responsible of the observed effects.     

A chromogenic calixarene hydroxamic acid for the sequential separation of Ti(IV) and Zr(IV)

A new chromogenic calixarene with hydroxamic acid as chelating agent was synthesized by partial reduction of nitrocalixarene which was subsequently coupled with coumarin chloride. The reagent showed selective and quantitative extraction of Ti(IV) into chloroform at 6 M HCl and that of Zr(IV) at 0.5 M HCl. A facile liquid-liquid extraction method for the separation and spectrophotometric determination of Ti(IV) and Zr(IV) has been proposed. The validity of the method was checked by separating several synthetic mixtures. The method was successfully applied to the analysis of piezoelectric lead-zirconium-titanate (PZT) samples. The method shows remarkable simplicity and selectivity. The method can also be used for the determination of Ti(IV) and Zr(IV) in various environmental samples. The article is published in the original.     

Titrimetric determination of uric acid with manganese(IV) sulfate

A simple indirect titrimetric determination of uric acid with manganese(IV) sulfate has been proposed. The method is stoichiometric and accurate and can be conveniently adapted for the assay of urinary uric acid.     

Extraction-spectrophotometric determination of germanium(IV) with mandelic acid and malachite green

A method has been developed for determination of germanium, based on complexation with mandelic acid and extraction of the ion-associate formed with Malachite Green (MG) into chlorobenzene. A weakly acidic aqueous solution (pH 2.5-3.5) at room temperature is used and indirect determination is achieved by measuring the absorbance of MG in the extract, at 628 mn. The calibration graph is linear over the range (0.17-8.63) x 10(-6) (0.05-2.50 mug of germanium); the apparent molar absorptivity is 1.33 x 10(5) 1.mole(-1).cm(-1). The interferences from Fe, Ti, Sn(IV), Mo, and SB(III) can be eliminated by addition of trans-1,2-diaminocyclohexanetetra-acetic acid and sodium diethyldithiocarbamate.     

Rapid extraction and photometric determination of cerium(IV) with N-p-tolylbenzohydroxamic acid (p-TBHA)

Summary A method for rapid extraction and spectrophotometric determination of cerium (IV) is described. The cerium-N-p-tolylbenzo-hydroxamic acid complex is extracted into chloroform at the pH 8.4 to 9.8. Maximum absorbance occurs between 460 and 470 nm. The values are reproducible at 465 nm and Beer's law is obeyed at this wavelength over the range of 0.03–40, per ml of the cerium(VI). The molar absorptivity of the cerium-p-TBHA complex is 4.6×10³ l · mole^–1 · cm^–2 at 465. An attempt has been made to determine the cerium in sea water.

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Zusammenfassung Eine Methode zur schnellen Extraktion und spektrophotometrischen Bestimmung von Cer(IV) wurde beschrieben. Der Cer-Komplex mit N-p-Tolylbenzohydroxamsäure wird bei pH 8,4–9,8 mit Chloroform extrahiert. Das Absorptionsmaximum liegt zwischen 460 und 470 nm. Bei 465 nm sind die Ablesungen reproduzierbar und wird das Beersche Gesetz zwischen 0,03 und 40g Cer/ml erfüllt. Die molare Extinktion des genannten Komplexes beträgt bei 465 nm 4,6 · 10³ l · mol^–1 · cm^–2. Es wurde versucht, den Cergehalt von Meerwasser zu bestimmen.