Extraction-photometric selective determination of trace perchlorates in potable waters

A method is proposed for the selective photometry determination of perchlorates in potable water with a detection limit of 2×10^?3 mg/L is proposed based on the extraction of its ion pair with the astrafloxin cation and absorbance measurements at 540 nm. The following ratios of matrix ions are acceptable (in parentheses): ClO^?, ClO ₂ ^? , ClO ₃ ^? , BrO ₃ ^? (500); I^? (1000); IO ₃ ^? (7000); HCO ₃ ^? , Cl^?,SO ₄ ^2? , NO ₃ ^? , Br^?, Na⁺, K⁺, Ca²⁺, Mg²⁺ (10000). The relative error of determination for ClO ₄ ^? is 20% in the range 4 × 10^-3-1 × 10^?2 mg/L and 10% in the range 1 × 10^-2–5 × 10^?2 mg/L.     

Using epichlorohydrin for a simultaneous increase of functional group hydrophilicity and spatial separation from the matrix of anion exchangers for ion chromatography

To increase the efficiency of anion exchangers based on copolymers of styrene and divinylbenzene in ion chromatography a new method for spatial separation and hydrophilization of functional groups using epichlorohydrin is suggested. Synthesis consists of acylation of a matrix by acetic anhydride, reductive amination by methylamine hydrochloride, alkylation of the aminated phase using epichlorohydrin, amination by dimethylamine at the terminal chlorine atom, and quaternization of the terminal amino group with epichlorohydrin. The obtained anion exchangers make it possible to simultaneously determine eight anions (F^?, HCOO^?, Cl^?, NO ₂ ^? Br^?, N ₃ ^? HPO ₄ ^3? and SO ₄ ^2? ) and demonstrate high efficiency (more than 62000 N/m for HPO ₄ ^2? ) in a suppressed ion-chromatography mode.     

EXAFS study of spin transition effect on the spatial and electronic structure of Fe(II) complexes with triazoles

EXAFS spectroscopy is used to investigate the characteristic features of the spatial and electronic structure of the polynuclear Fe(II) complexes Fe(ATR)₃A₂ (where A is the NO ₃ ^? , BF ₄ ^? , Br^?, or ClO ₄ ^? anion and ATR is 4-amino-1,2,4-triazole) and their magnetically diluted phases Fe_xZn_1?x(ATR)₃(NO₃)₂. The absolute distances from Fe and Zn to the surrounding atoms are determined at temperatures higher and lower than the spin transition point. In all complexes, the spin transition is accompanied by significant changes in the local environment of Fe atoms, while in the magnetically diluted phases the surrounding of zinc remains unchanged. It is shown that addition of Zn atoms distorts the triazole rings in the low-spin state of the complexes. No localized anions were revealed within 3.3 Å from the Fe and Zn atoms. It is shown that a decrease in the spin transition temperature correlates with an increase in Fe?N distances in the low-spin complexes due to magnetic dilution and substitution of anions in the series NO ₃ ^? , BF ₄ ^? , Br^?, ClO ₄ ^? of ATR-containing complexes.     

The conformational changes of 5SrRNA from lupin seeds in presence of ClO 4 − , NO 3 − , Br−, BF 4 − , SO 4 2− , Cl−, COO− anions by adiabatic scanning calorimetry

The results of calorimetric studies of 5SrRNA solutions isolated from lupin seeds in the pressence of the ClO ₄ ^? , NO ₃ ^? , Br ₄ ^? , SO ₄ ^2? , Cl^?, COO^? (maleic and fumaric acids) anions were reported. The plots of calorimetric curves, enthalpy of conformational changes of two state transitions were presented. Using the deconvolution method proposed by Freire and Biltonen the elementary transitions were distinguished and discussed.     

The effect of substituents in ligands and of anionic composition on the exchange interaction in binuclear Cu(II) complexes based on 2,6-diformyl-4-methylphenol

A series of novel binuclear Cu(II) complexes based on 2,6-diformyl-4-methylphenol and containing aminoguanidine and hydrazinobenzthio(oxo)zole as variable chelatophore fragments were synthesized. In these complexes, Cl^?, Br^?, NO ₃ ^? , and ClO ₄ ^? are both the inner-and outer-sphere ions. The magnetochemical properties of the title complexes were compared and the anion nature was shown to influence the structure of the complexes and the strength of antiferromagnetic interaction.     

Auftrennung von gemischten Hexa(bromochloro)-rhenaten(IV) und -osmaten(IV) auf Dünnschichtcelluloseplatten

The ions ReBr_nCl _6?n ^2? (0?n?6) and OsBr_nCl _6?n ^2? , respectively, ReO₄ ^? and Br^? have been separated on cellulose using the thin-layer chromatographic technique with 3.2 M sulphuric acid as the mobile phase.     

Comparison of chemical effects of UV radiation from spark discharge in air and a low-pressure mercury lamp

The chemical effects of UV radiation from atmospheric-pressure spark discharge and a DBK-9 low-pressure mercury lamp in distilled water and aqueous solutions of hydrogen peroxide and tryptophan have been studied. Reactive species generated in water by the both radiation sources are HO ₂ ^· radicals, acid residue ions NO ₂ ^? and NO ₃ ^? , and ammonium ions. The yield of HO ₂ ^· radicals has appeared to be the same for both sources, (1.1–1.2) × 10^?6 mol L^?1 s^?1. This is confirmed by measurements of the degradation kinetics of tryptophan, which can be destroyed by HO ₂ ^· radicals. The pH of water monotonically decreases with time during the spark discharge treatment. In the case of the mercury lamp, the pH varies insignificantly because of the competition of NH ₄ ⁺ alkali ions with the acid residues. UV radiation plays the major role in the decomposition of hydrogen peroxide.     

Adsorption studies of the removal of anions from aqueous solutions onto an adsorbent prepared from wheat straw

Modified wheat straw (MWS) was prepared by the grafting of epichlorohydrin, triethylamine and ethylenediamine onto WS. The characteristics of MWS and its adsorption capacity for NO ₃ ^? , PO ₄ ^3? and Cr₂O ₇ ^2? were investigated. The results indicate that amine groups with positive charge have been introduced into the structure of MWS, and significantly increased its anion adsorption property. The functions of MWS dosage, the solution pH, the contact time and temperature have significant influence on the adsorption process, and the adsorption is well fitted with the Langmuir equation and pseudo second-order model. The maximum adsorption capacity of MWS for NO ₃ ^? , PO ₄ ^— (P) and Cr₂O ₇ ^2? (Cr) is 53.5, 62.4 and 386.2 mg g^?1, respectively.     

Fractionation of europium isotopes in extraction systems: Eu(III), HDEHP/Eu(III), H+ (Cl−, NO 3 − , SO 4 2− ). Ligand isotope effect

The^151/153Eu isotope effects were investigated for the lignad exchange reaction between Eu(III) ions in the extraction system: [Eu(III),di(2-ethylhexyl) phosphoric acid]_org?[Eu(III), H⁺A^?(A^?=Cl^?,NO ₃ ^? ,SO ₄ ^2? )]_aq. It was observed that the heavy isotope¹⁵³Eu was preferentially fractionated into the organic phase. The following values of the unit separation gains, ε=ln(q), were found: 7.3·10^?5 for Cl^?, 13.0·10^?5 for NO ₃ ^? , and 9.4·10^?5 for SO ₄ ^2? . The direction of the effect was opposite, and its absolute value was about one order of magnitude lower, in respect to the effect observed in the redox exchange, Eu(II)?Eu(III), in a similar extraction system.     

Structures of NO 3 − formed via glow discharge in atmospheric gases

Tandem mass spectrometry experiments using both ion-molecule reactions and collision-induced dissociation (CID) in an ion trap mass spectrometer have been performed to characterize the structures of the NO ₃ ^? ions that issue from an atmospheric sampling glow discharge ionization source. The experimental evidence suggests that significant abundances of at least two stable forms of NO ₃ ^? can be obtained from an air-sustained glow discharge. Ab initio calculations have been performed to identify the structures of the likely isomers. Rate constants have been measured for the reaction of the less thermodynamically stable isomer(s) with carbon dioxide, and evidence is given for a new reaction, (OO?NO)^? + NO ₂ ^? → NO ₂ ^? + O₂ + NO^?. The combination of em with a kinetic study is shown to be a useful approach for obtaining rate constant information when a mixture of reactive and unreactive isomers is present in the reactant population.     

Spontaneous disproportionation of NO2 (N2o4) by aromatic hydrocarbons. Formation of nitrosonium EDA complexes as chemical intermediates

Strong (orange/red) colourations resulting immediately upon the exposure of nitrogen dioxide and its equilibrium dimer (dinitrogen tetroxide) to various aromatic hydrocarbons (ArH) are shown to arise from the nitrosonium EDA or electron donor-acceptor complexes [ArH, NO⁺NO ₃ ^? ]. The latter exhibit diagnostic charge-transfer absorptions and characteristic N-O stretching bands in the UV-vis and IR spectra, respectively, that relate directly to ArH/NO⁺ interactions extant in the EDA complexes previously derived from the authentic nitrosonium salt, NO⁺PF ₆ ^- . Time-resolved picosecond spectroscopy establishes the charge-transfer excited state of [ArH, NO⁺NO ₃ ^? ] to be essentially identical to that from [ArH, NO⁺BF ₄ ^? ]. Furthermore, the same temporal decay of the spectral transients (ArH^+?) from both systems indicates minimal ion-pairing effects of the counterions (NO ₃ ^? and BF ₄ ^? ) on the kinetics of back electron transfer.     

Formation of O 2 − in charge transfer collisions of fast molecular hydrogen ions with O2 molecules

Cross sections for the production of O ₂ ^? in charge transfer collisions of fast molecular hydrogen ions (H ₂ ⁺ , D ₂ ⁺ , H ₃ ⁺ , and D ₃ ⁺ of 10 to 140 keV kinetic energy) with O₂ molecules have been determined by means of a time-of-flight mass spectrometer analysing the slow negative product ions from the collisions. Within the measuring accuracy equivelocity H ₂ ⁺ and D ₂ ⁺ ions have the same cross sections for the generation of O ₂ ^? . The projectile velocity dependence curve of the cross section passes through a broad maximum with a peak value of about 6.5×10^?18 cm² around the Bohr velocity (25 keV/u) before showing an asymptotic decrease still within the limited energy range under investigation that is in inverse proportion to the square of velocity. Throughout the examined energy range H ₃ ⁺ ions yield a cross section which is about 1.4 times larger than that of H ₂ ⁺ ions of the same velocity. The fragment ion O^? has been found to appear with cross sections between 10^?19 and 10^?18 cm² upon collisional excitation in the energy range under investigation, with ever decreasing intensity when the energy of the positive hydrogen ions, the proton included, was increased.     

A selective fluorescent and colorimetry competition assay for fluoride ions in DMSO media based on 4-chloro-2,6-bis(hydroxymethyl) phenol

We report here a selective, efficient and very simple receptor which can easily detect F^? in the presence of a wide range of other anions [Cl^?, Br^?, I^?, HSO ₄ ^? , NO ₃ ^? , Acetate (AcO ^?) and Benzoate (BzO ^?)] by use of colorimetric or fluorometric detection. 4-Chloro-2,6-bis(hydroxymethyl) phenol (CBHMP) is a simple and available phenolic receptor having no special chromophoric function. In this colorimetric method, naked-eye detection of F^? with CBHMP is described. Interestingly, fluorometric detection of F^? is also possible by highly selective fluorescent quenching response CBHMP in dimethyl sulfoxide (DMSO) media.     

Boric acid

pH ranges of existence of boric acid and its ionic species H₂BO ₃ ^? , HBO ₃ ^2? , BO ₃ ^3? , and B(OH) ₄ ^? in aqueous solutions are calculated using Mathcad software package.     

Effect of inorganic ions on the photocatalytic degradation of humic acid

The article studies on the effects of six inorganic ions (Ca²⁺, Mg²⁺, Cl^?, SO ₄ ^2? , H₂PO ₄ ^? , and HCO ₃ ^? ) on titanium dioxide (TiO₂)-based photocatalytic degradation of humic acid (HA). We focus on the effects of the inorganic ions on HA characters, adsorption of HA on TiO₂ and photocatalytic degradation of HA. The results indicate that Ca²⁺ and Mg²⁺ with HA can form complexes which can decrease the solubility of HA, and then increase the HA adsorbed on TiO₂. However, the complex is more difficult to be degraded than HA. The effects of Cl^? and SO ₄ ^2? are closely related to their influences on HA solubility. The solubility changes of HA to some extent can enhance the adsorption of HA on TiO₂, and promote the photocatalytic degradation. Nevertheless, great solubility decreasing of HA can weaken the photocatalytic degradation. HCO ₃ ^? and H₂PO ₄ ^? can inhibit the photocatalytic degradation process seriously, because HCO ₃ ^? and H₂PO ₄ ^? are the strong scavengers of hydroxyl radicals, and can weaken the adsorption of HA on TiO₂ due to adsorption competition.     

Anion chromatography and redox photometry in potable water analysis

Anion chromatography with ANIEKS-N selective ion exchanger and redox photometry with an antimony(V) ionic associate as selective oxidizing agent were suggested for determination of low concentrations of toxic (F^?, Br^?, NO ₂ ^? , NO ₃ ^? ) and biogenic (SeO ₃ ^2? , I^?) ions in some potable waters available from central water supply systems and mineral water springs.     

Oxidation and reductive bromination of Bis(4-tert-butylphenyl)aminoxyl

One-electron oxidation of bis(4-tert-butylphenyl)aminoxyl with antimony pentachloride and bromine leads to the formation of oxoammonium salts with anions SbCl ₆ ^? and Br ₃ ^? respectively. The salt with the Br ₃ ^? anion converted at heating into a mixture of bromodiphenylamines which formed also from the aminoxyl as a result of previously unknown reaction of three-electron reductive bromination. The mechanisms of these reactions were assumed.     

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate species H₃PO ₄ ⁰ (aq),H₂PO ₄ ^? (aq),HPO ₄ ^2? (aq) or PO ₄ ^3? (aq). Many divalent, trivalent and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation require comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier, with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ?mol^?1 per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq) ions at 298.15 K and p?° =1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S _m ^o (H₂PO ₄ ^? , aq, 298.15 K) = (90.6±1.5) J?K^?1?mol^?1 was obtained.     

Thermodynamics of extraction of tetravalent plutonium,uranium, thorium and zirconium

Thermodynamic treatment of the experimental data on the extraction of quadrivalent Pu, U, Th and Zr with tri-n-butyl phosphate (TBP) from nitric acid solutions is presented. It is shown that the extraction of all the quadrivalent metals studied is going according to the same mechanism: M(OH)^4?i+(4?i)NO ₃ ^? +2TBP?M(OH)_i(NO₃)_4?i·2 TBP. For Zr, i=0, 1, and 2; for the remaining M(IV), i=0 and 1. The thermodynamic constants of extraction of M(IV) with the kerosene solutions of TBP according to the above mentioned equation are as follows: Zr: K ₀ ⁰ =0.6; K ₁ ⁰ =14; K ₂ ⁰ =5. Pu: K ₀ ⁰ =380; K ₁ ⁰ =4.8·10⁴. U: K ₀ ⁰ =300; K ₁ ⁰ =1.8·10⁴. Th: K ₀ ⁰ ～150. It has been established that Zr and Pu(IV) are extracted into 2-thenoyltrifluoracetone (HA) from perchloric acid solutions under the formation of MA₄ and M(ClO₄)A₃ species. For the extraction from nitric acid solutions, the species formed are ZrA₄ and Zr(NO₃)A₃ in the case of Zr, PuA₄ and Pu(OH)A₃ in the case of Pu. The differences in the qualitative and quantitative characteristics of the extraction of M(IV) with TBP and HA from nitric and perchloric acids are explained by the effect of the character of the acid and of ionic potential upon the structure of the hydration shell of M _aq ⁴⁺ .