Spectrophotometric determination of chloride in waters using a multisyringe flow injection system

A multisyringe flow injection system (MSFIA) with spectrophotometric detection is proposed as a fast, robust and low-reagent consumption system for the determination of chloride (Cl⁻) in waters. The system is based in the classic reaction of Cl⁻ with Fe³⁺ and Hg(SCN)₂, but due to the hazardous properties of this last reagent, the proposed methodology has been developed with the aim to minimize the consumption of this one, consuming less than 0.05 mg of Hg for a Cl⁻ determination, being the system of this type with the lowest Hg consumption. The linear working range was between 1 and 40 mg L⁻¹ Cl⁻ and the detection limit was 0.2 mg L⁻¹ Cl⁻. The repeatability (RSD) was 0.8% for a 10 mg L⁻¹ Cl⁻ solution, and the injection throughput was 130 h⁻¹. The proposed system is compared with other chloride monitoring flow systems, this comparison is realized with a point of view of the equilibrium between the obtained analytical features and produced residues toxicity. The proposed system was applied to the determination of Cl⁻ in mineral, tap and well water.     

Can chlorine anion catalyze the reaction of HOCl with HCl?

The reaction of HOCl + HCl → Cl₂ + H₂O in the presence of chlorine anion Cl⁻ has been studied using ab initio methods. The overall exothermicity is 15.5 kcal mol⁻¹ and this reaction has been shown to have a high activation barrier of 46.5 kcal mol⁻¹. Cl⁻ is found to catalyze the reaction via the formation of HOCl·Cl⁻, ClH·HOCl·Cl⁻ and Cl⁻·H₂) intermediate ion-molecule complexes or by interacting with a concerted four-center transition state of the reaction of HOCl + HCl.     

Modeling the separation performance of nanofiltration membranes for the mixed salts solution

A new model is proposed to evaluate the separation performance of nanofiltration (NF) membranes for the mixed salts solution. In the model, the observed transmission of an ion through a NF membrane is applied to express the separation performance of the membrane for the ion in the mixed salts solution, which has a relationship with the total concentration, the equivalent fraction and the species of each ion in the mixed salts solution. The verification of the model was carried out in the permeation experiments of some mixed salts solutions ((1) Na⁺, Cl⁻ and F⁻; (2) Na⁺, K⁺ and Cl⁻; (3) Na⁺, F⁻, Cl⁻ and NO₃⁻; (4) Na⁺, Cl⁻, NO₃⁻ and SO₄²⁻) through three commercial NF membranes (ESNA 1-LF, ESNA 1 and LES 90). According to the permeation experiments of three NF membranes for some binary salts solutions, the competition coefficients of ions were obtained. The model evaluation results agreed quite well with the experimental data. Finally, the model was applied to evaluate the observed transmission of each ion in the mixed salts solution (Na⁺, F⁻, Cl⁻, NO₃⁻ and SO₄²⁻) through three NF membranes. The agreement between the model evaluation results and the experimental data indicated that the model is suitable for evaluating the separation performance of three NF membranes for the mixed salts solution.     

Interactions of mercury(II), lead(II), calcium(II), aluminium(III) or ferric(III) nitrate with single and double chain linear alkylbenzenesulfonates in aqueous and sea-water media

The solubility products of mercury(II) and lead(II) dodecylbenzenesulfonates were calculated on the basis of light scattering measurements at 20°C to be (9.33 ± 0.90) × 10⁻¹³ and (1.03 ± 0.10) × 10⁻¹² respectively. The investigations of precipitation phenomena performed in diluted natural sea-water ([Cl⁻] = 10⁻¹² mol dm ⁻³), including tenside and added heavy metal ions, showed similar behaviour for all metal dodecylbenzenesulfonates investigated in this work, i.e. the synergistic effect of tenside, of added electrolyte, and of cations and anions from sea-water. A comparison made by a statistical test of significance, chosen to measure agreement between the estimates of the solubility constants obtained in aqueous solutions and in the above mentioned sea-water solution, showed a noticeable effect, evident particularly in the case of mercury(II). The precipitation of tenside and metal nitrates in natural sea-water ([Cl⁻] = 5 × 10⁻¹ mol dm⁻³) covers a wide concentration region of dodecylbenzenesulfonic acid (from high concentrations to 5 × 10⁻⁶ mol dm⁻³) and from high metal nitrate concentrations to very low. The microscopic textures of phases precipitated in the systems with sea-water obviously confirmed favouring formation of the liquid crystalline phase.     

Role of axial ligand on the electronic structures of active intermediates in cytochrome P-450, peroxidase and catalase

DFT method (B3LYP) with 6-31G^* basis set was utilized in the computation of a fully optimized structure, net atomic charges and spin densities of the intermediate of cytochrome P-450-oxoiron(IV) porphyrin cation radical, compound I – in the presence of axial ligand such as thiolate (SMe⁻) imidazole (IM), phenoxide (OPh⁻), methoxide (OMe⁻) and chloride (Cl⁻). The results show doublet states in compound I are about 2–4 kcal/mol more stable than quartet states for all aforementioned ligands, and the doublet state is the ground state in all cases. However, electron donor ability of the ligands are in the order of SMe⁻ > IM > OMe⁻ > OPh⁻ > Cl⁻. Also the active oxidant intermediate of cytochrome P-450 between different mesomeric structures select sulfur oxygen radical type structure and can be viewed as (RS^↓)Fe^↑(IV)(O^↑)(Por). In horseraddish peroxidase (HRP) and peroxidase with histidine axial ligand π cation radical character of porphyrin ring is preferred (Im)Fe^↑(IV)(O^↑)(Por^↓). For the ligands such as OMe⁻, OPh⁻ and Cl⁻ oxidation mainly took place on the iron and the active intermediate can be viewed as (L)Fe^↑(V)(O)(Por) with one unpaired electron localized on the iron.     

Ion chromatography of organic-rich natural waters from peatlands: I. Cl, NO2, Br, NO3, HPO4, SO4 and oxalate

Organic-rich natural waters from peat bogs in continental (Switzerland) and maritime (Shetland Islands, Scotland) areas were analysed for Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻, SO₄²⁻ and oxalate using ion chromatography. These anions can be determined simultaneously in the surface and pore water samples from the continental bogs using a 250-μl injection loop. Using this loop, the detection limits were ca. 5 ng/g for the monovalent anions and SO₄²⁻ and 10 ng/g for HPO₄²⁻ and oxalate. An organics-removal cartridge (Dionex OnGuard P) was used to remove humic materials. These cartridges did not significantly affect the measured concentrations of anions in blind standards. Analyses of deionized water treated with these cartridges are not significantly different from those for untreated deionized water. For the maritime bogs, the relatively high concentrations of Cl⁻ (more than 100μ/g in many samples) and SO₄²⁻ (up to 50 μg/g) require two separate determinations for complete analyses. A 10-μl injection loop was used to determine Cl⁻, Br⁻ and SO₄²⁻. A 250-μl injection loop was used to measure NO₂⁻, NO₃⁻, HPO ₄²⁻ and oxalate. In each instance a Dionex OnGuard P cartridge was used to remove humic materials. In addition, a chloride-removal cartridge (Dionex OnGuard AG) was used to remove Cl⁻ when the larger injection loop was used. This cartridge has no significant effect on the measurement of HPO_4-²⁻ at concentrations of 20 ng/g. In each of the bog water chromatograms there were usually a number of unknown peaks. These are probably due mainly to organic anions.     

Spectrophotometric study of complexation equilibria between HCrO4 and Cl ions

The complex equilibria between HCrO₄⁻ and Cl⁻ ions has been studied spectrophotometrically at a constant ionic strength of 3.0 mol dm⁻³ and the data have been analyzed both graphically and numerically by means of the program LETAGROP-SPEFO (L. G. Sillen and B. Warnquist, Arkiv. kemi. 1968, 31, 377). The experimental results can be explained on the basis of the following reaction: HCrO₄⁻+H⁺+Cl⁻ = CrO₃Cl⁻+H₂O (log β₁₁ = 1.37±0.08). Molar absorptivities of HCrO₄⁻ and CrO₃Cl⁻ were also reported.     

Studies on elution conditions for the determination of anions by supressed ion-interaction chromatography using a graphitized carbon column

A new method has been developed for ion-interaction chromatography with suppressed conductivity detection and a new graphitized carbon packing, which is sintered from carbonic material at a high temperature. Combinations of various eluting agents, tetrabutylammonium hydroxide (TBA) and acetonitrile have been investigated to optimize the separation of eight common anions (F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, SO₄²⁻, HPO₄²⁻ and I⁻). Calibration curves were linear from 0.5 to 10 μg/ml for F⁻, from 1.0 to 20 μg/ml for Cl⁻, NO₂⁻ and NO₃⁻, from 2.5 to 50 μg/ml for Br⁻ and SO₄²⁻ and from 5.0 to 100 μg/ml for HPO₄²⁻ and I⁻ with a correlation coefficient (r) of 0.999 or better. The relative standard deviations (R.S.D.s) of peak areas were between 0.2 and 0.9% for 10 repeated measurements. The application of this newly developed method was demonstrated by the determination of chloride, bromide and sulfate in pharmaceutical compounds using the direct injection method. The analytical results were within ±2% (relative) of the theoretical value, and thus in good agreement with the theoretical value for each sample.     

Two-component density functional theory of positron binding to negative ions

The problem of binding in positron-negative ion systems has been addressed via two-component density functional theory. Calculations have been performed within the local density approximation for electron exchange-correlation as well as for the electron-positron correlation potential using a self-interaction corrected version of the density functional equations. Our results indicate that a positron forms a stable bound state with the negative ions Li⁻,B⁻,C⁻,O⁻,F⁻ and Cl⁻ with respect to dissociation into a negative ion and a positron or a neutral atom and positronium. Inclusion of electron-positron correlation deepens the positron bound state and stabilizes the system compared to earlier exchange-only calculations.     

Neutron diffraction studies of ions in aqueous solution

The effect of ions on the structure of water is discussed in terms of results for ionic hydration as derived from neutron diffraction isotopic substitution experiments. Results are presented for alkali ions (Li⁺, Na⁺ and K⁺), alkaline earth ions (Mg²⁺, Ca²⁺ and Sr²⁺) and for the anions Cl⁻, ClO⁻₄) and NO⁻₃, from which it is inferred that the water structure is disrupted more by cations with higher charge density.     

Effect of Several Anions on Fe-Based Catalyst for Fischer-Tropsch Synthesis

The influence of several anions on Fe-based Fischer-Tropsch catalyst,used in the synthesis of light olefins from synthesis gas,was studied.The results indicated that the addition of anions resulted in the reduction of catalytic activity.When the anion content in the catalyst was 500 ppm,the influence of different anions on the catalysis activity was as follows:S~(2-)>Cl~->SO_4~(2-)>NO_3~-.The addition of S~(2-)improved the selectivity of total hydrocarbons in the products,and Cl~- reduced this selectivity but increased the olefin content in the total hydrocarbons at the same time.When the contents of S~2 and Cl~- in the catalyst were less than 50 ppm,their influence could be ignored.The XRD results indicated that the addition of anions reduced the contents ofα-Fe and Fe_3C,which were the active components in the catalyst.     

Specific adsorption of halogen anions on hydrous γ-Al2O3

The paper reports results of a study on the specific adsorption of F⁻, Cl⁻, Br⁻, I⁻, ClO₃⁻, BrO₃⁻, IO₃⁻ and IO₄⁻ on hydrous γ-Al₂O₃. The isotherms of the anion adsorption and the adsorption dependencies on pH and the ionic strength of the solution have been determined under the equilibrium conditions. According to the degree of affinity to γ-Al₂O₃, the anions can be ordered as: I⁻3⁻−−3⁻3⁻4⁻−. It has been established that the sorption of IO₄⁻ and F⁻ involves the formation of surface complexes in the inner co-ordination sphere, whereas that of Cl⁻, Br⁻, I⁻, ClO₃⁻, BrO₃⁻ and IO₃⁻ takes place through formation of ion pair complexes in the outer co-ordination sphere. In the dynamic system, the exchange isoplanes and elution curves have been determined for selected anions on columns filled with Al₂O₃. It has been shown that γ-Al₂O₃ can be used for isolation and concentration of IO₃⁻ from natural waters in order to decrease the limit of the ions determination to 2 μg l⁻¹. Using differential pulse voltammetry (DPV), after isolation and concentration on γ-Al₂O₃, the content of iodates has been determined in mineral, marine and tap water doped with these ions.     

Manipulation of separation selectivity of inorganic anions in electrostatic ion chromatography by the use of mixed cationic–zwitterionic micelles as the column coating solution

This paper describes an electrostatic ion chromatographic system in which the separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitterionic and cationic surfactants in the column coating solution used to prepare the stationary phase. The zwitterionic surfactant used for this study was 3-(N,N-dimethyltetradecylammonio)propanesulfonate (Zwittergent-3-14) and the cationic surfactant was tetradecyltrimethylammonium (TTA). Using a reversed-phase C₁₈ column (250×4.6 mm I.D.) coated with 10/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the stationary phase and either NaHCO₃ or Na₂CO₃ aqueous solution as the eluent, together with suppressed conductivity detection, baseline separation of seven model inorganic anions was obtained. The elution order for those anions was found to be F⁻4²⁻−4²⁻2⁻−3⁻. Under the same conditions but using 1/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the column coating solution, the elution order for these model ions was F⁻4²⁻4²⁻−2⁻−3⁻. The early elution of phosphate and sulfate is a unique attribute of this system. Detection limits for F⁻, HPO₄²⁻, Cl⁻, SO₄²⁻, NO₂⁻, Br⁻ and NO₃⁻ (S/N=3, sample injection volume 100 μl) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 μM, respectively.     

A hyodeoxycholic acid-based molecular tweezer: a highly selective fluoride anion receptor

A new molecular tweezer receptor Hc1 based on hyodeoxycholic acid has been synthesized and its binding properties were accessed by ¹H NMR and isothermal titration calorimetry experiments. Molecular tweezer Hc1 shows a high selectivity toward F⁻ over Cl⁻, Br⁻, I⁻, and H₂PO₄⁻.     

π-facial interactions between Cl and [S4N3]. X-ray crystal structure of [S4N3]Cl

The X-ray structure of [S₄N₃]Cl reveals three independent molecules, which all display π-facial interactions between the Cl⁻ and the pseudo-aromatic [S₄N₃]⁺ rings to produce a structure containing “inverse sandwich” systems.     

Field investigation of major and minor ions along Summit (Central Greenland) ice cores by ion chromatography

As a part of the European EUROCORE and GRIP (Greenland Ice Core Project) operations aimed at recovering deep ice cores at Summit (Central Greenland), we have for the first time successfully performed ion chromatography measurements in the field and investigated in detail the soluble impurities, including Na⁺, NH⁺₄, K⁺, Mg²⁺, Ca²⁺, F⁻, CH₃COO⁻, CH₂ OHCOO⁻, HCOO⁻, CH₃SO₃⁻, Cl⁻, NO⁻₂, SO₄²⁻ and C₂O₄²⁻, trapped in ice deposited over some 200 000 years in Greenland.     

Note on the titration of iodide by the Andrews method

For a satisfactory determination of iodide by Andrews' method, the concentration of hydrochloric acid in the solution should not fall below 3N. A high concentration of each ion is required; that of chloride ion is much greater than is needed for conversion of ICl to ICl₂⁻. The effects of varying the concentrations of H⁺, Cl⁻ and indifferent ions on the rate of the slow stage (oxidation of I₂ to ICl) are demonstrated.     

Predictive schemes for the reactivity of borane carbonyl and the stability of carbonyltrihydroborate anions, BH3C(O)X

The reactivity of borane carbonyl (BH₃CO) and its isoelectronic counterpart the acetylium cation (CH₃CO⁺) are compared resulting in the formulation of (carbonyl)trihydroborate anions, BH₃C(O)X⁻, which are isoelectronic and isostructural with organic carbonyls. By analogy with the ease of reduction of organic carbonyl compounds by hydroborate, the relative stability towards self-reduction-oxidation (hydride transfer from boron to carbonyl carbon) in BH₃C(O)X⁻ is proposed. The postulated order, with increasing stability is BH₃C(O)Cl⁻ < BH₃C(O)H⁻ < BH₃C(O)R⁻ < BH₃C(O)OR⁻ < BH₃C(O)NR⁻₂ < BH₃C(O)O²⁻. Experimental results of this study together with known chemistry are shown to be consistent with the proposed order. Further, it is suggested that a similar predictive scheme may be applicable to the chemistry of the amine-carboxyboranes (boron analogues of -amino acids) and their derivatives.     

Cooperative two-photon-induced chemical bond formation during a Kr+F2 collision to form KrF

The reactive Kr⁺F₂⁻ potential energy surface is probed by two-photon, laser-induced chemical bond formation during a Kr+F₂ collision. This is compared with the pulsed laser excitation (two-photon) of Kr(2p₉) followed by collision with F₂ leading to the formation of KrF(B, C). In addition to reporting the excitation spectrum for the two-phonon-induced collision process, these techniques were used to determine quenching rate constants of Kr₂F^*. Quenching by Xe gives XeF(B, C) with rate constant (1.5±0.2)×10⁻¹⁰ cm³ s⁻¹; the quenching rate constant for F₂ is (1.5±0.2)×10⁻¹⁰ cm³ s⁻¹, and the radiative lifetime of Kr₂F^* is 240±35 ns. The quenching rate constant for the coupled Kr(2p₈) and Kr(2p₉) levels by F₂ is (13±2)×10⁻¹⁰ cm³ s⁻¹.     

X-Ray, MP2 and DFT studies of the structure and vibrational spectra of homarinium chloride

The effects of hydrogen bonding, inter- and intramolecular electrostatic interactions on the structure of homarinium chloride, HOMH·Cl, in the crystal and its isolated molecule have been studied by X-ray diffraction, FT-IR, Raman, ¹H and ¹³C NMR spectroscopies, and by the MP2 and DFT theoretical methods. In the crystal, the Cl⁻ anion is connected with protonated homarine via the O–HCl⁻ hydrogen bond of the length of 2.937(4) Å, and two N⁺Cl⁻ intermolecular electrostatic interactions. In the isolated molecule, according to the MP2 and B3LYP calculations, the Cl⁻ anion is engaged in a shorter hydrogen bond (O–HCl⁻ of 2.811–2.861 Å) and in one type of intramolecular electrostatic interactions. The calculated bond lengths and bond angles at the MP2 and B3LYP levels of theory are in good agreement with the X-ray data, except the conformation of the COOH group, which is cis (syn) in the crystal and trans (anti) in the isolated molecule. The tentative assignments for the experimental solid state vibrational spectra of HOMH·Cl and HOMD·Cl have been made on the basis of the B3LYP/6-31G(d,p) calculated frequencies and intensities. The effect of quaternization of picolinic acid on the chemical shifts of the ring protons and carbons is analyzed.