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.     

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.     

Spectres infrarouges et structure des anions 2-methylallyle, CH3-C(CH2)2- et triméthylèneméthane, C(CH2)3

The infrared spectra of solid samples of C₄H₇K and C₄D₇K have been investigated in the 4000 to 30 cm⁻¹ range. A complete assignment of intramolecular fundamentals of C₄H₇⁻ and C₄D₇⁻ ions and of potassium-allyl vibrations is proposed and the intramolecular force constants are calculated. The C(CH₂)₃²⁻ anion has been identified spectroscopically. Structures of C₃H₅⁻, C₄H₇⁻ and C(CH₃)₃²⁻ are discussed and compared with those optimised by the MINDO/3 method.     

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.     

Influence of operating conditions on the retention of phosphate in water by nanofiltration

The objective of this study was to investigate the retention of phosphate anions, H₂PO₄⁻ and HPO₄²⁻, by nanofiltration. The first part of this study deals with the characterisation of the NF200 membrane used in permeation experiments with aqueous solutions of neutral organic and charged inorganic solutes. In the second part the effects of feed pressure, ionic strength, concentration and pH on the retention of phosphate anions were investigated. Results show that the membrane is negatively charged, its pore radius is around 0.5 nm and the retention order for the salts tested was R(Na₂SO₄) > R(NaCl) > R(CaCl₂). The retentions of phosphate anions are in the order of 85% for H₂PO₄⁻ and 96% for HPO₄²⁻. They are relatively high when compared to retentions of other anions with the same charge. The retentions of phosphate anions, particularly the monovalent species, depend on the chemical parameters (feed concentration, ionic strength, and pH) and applied pressure. The experimental data were analysed using the Speigler–Kedem model and the transport parameters, i.e., the reflection coefficient (σ) and solute permeability (P_s) have been determined.     

Simultaneous determination of anions and cations by ion-exclusion chromatography–cation-exchange chromatography with tartaric acid/18-crown-6 as eluent

Ion-exclusion chromatography–cation-exchange chromatography was developed for the simultaneous separation of common inorganic anions and cations (Cl⁻, NO₃⁻ and SO₄²⁻; Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) on a weakly acidic cation-exchange column by elution with weak acid. Generally, the resolution among these monovalent cations was only moderate, thereby hindering the determination of these analytes in natural-water samples. Therefore, 18-crown-6 was added to the eluent to improve the resolution. A good separation of these anions and cations on a weakly acidic cation-exchange column was achieved in 30 min by elution with 5 mM tartaric acid/6 mM 18-crown-6/methanol–water (7.5:92.5). The ion-exclusion chromatography–cation-exchange chromatography method developed here was successfully applied to the separation of major anions and cations in an environmental water sample.     

Persulphate quenching of the excited state of ruthenium(II) tris-bipyridyl dication: thermal reactions

The rate constant for the reaction between the sulphate radical (SO₄^√−) and the ruthenium (II) tris-bipyridyl dication (Ru(bipy)₃²⁺) is (3.3±0.2)×10⁹ mol⁻¹ dm³ s⁻¹ in 1 mol dm⁻³ H₂SO₄ and (4.9±0.5)×10⁹ mol⁻¹ dm³ s⁻¹ in 0.1 mol dm⁻³, pH 4.7 acetate buffer. The SO₄^√−radical produced by the electron transfer quenching of Ru(bipy)₃^2+* by S₂O₈²⁻ reacts rapidly with both acetate buffer and chloride ions. These side reactions result in a reduction in the overall quantum yield of Ru(bipy)₃³⁺ production and reduced reaction selectivity when Ru(bipy)₃^2+* is quenched by persulphate.     

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.     

High-performance ion chromatography applied to free-radical mechanisms in drug design the problem of ion analysis at high ionic strengths

Putative free-radical intermediates in drug action can be studied by radiolysis of model systems containing low concentrations of drug and much higher concentrations of other solutes to scavenge the primary water radicals and convert them into appropriate oxidants or reductants. The need to employ high ionic solute concentrations (typically >10 mmol dm⁻³) represents a challenge for the high-performance ion chromatographic detection of drug-derived ions (typically, <50 μmol dm⁻³). Constraints on the chromatographic method chosen are illustrated with examples of the application of high-performance ion chromatography (HPIC) to radiation chemistry studies in the oxidative decar☐ylation of the anti-tumour drugs flavone-8- and xanthenone-4-acetic acids and structurally related aromatic car☐ylic acids (CO₂ in the form of CO₃²⁻), the oxidative denitrification of nitric oxide precursor molecules (NO in the form NO₂⁻/NO₃⁻) and the generation of SO₄²⁻ from novel thiol-based (perthiol) drugs.     

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.     

Photodegradation of a textile dye catalyzed by sol–gel derived nanocrystalline TiO2 via ultrasonic irradiation

Nanocrstalline pure anatase titania were prepared by sol–gel process at room temperature followed by ultrasonication (Ti–US). The photocatalytic activity of Ti–US has been evaluated by the degradation of textile dye, Methylene Blue in presence and absence of common inorganic salts (NO₃⁻, C₂O₄²⁻, SO₄²⁻, citrate). It was observed that, in presence of anions, the degradation of the dye increases significantly. The influence of the presence of H₂O₂ on the degradation rate was studied. The dependence of photodegradation of the dye rates on various parameters such as dye concentration, photocatalyst concentration and pH were also investigated. The photodegradation rate follows first order kinetics. H₂O₂ and UV light have a negligible effect in absence of Ti–US catalyst. The relative photonic efficiency of the system is reported using phenol as a standard organic compound.     

Temperature dependence of adlayers on Pt(1 1 1) and Au(1 1 1) in a sulfuric acid solution studied by in situ IRAS

Temperature dependence studies of adsorption of sulfuric acid species on Pt(1 1 1) and Au(1 1 1) electrodes were carried out using in situ infrared reflection absorption spectroscopy. A temperature-dependent shift of the interconversion potential between HSO₄⁻/H₃O⁺ and H₂SO₄ on a Pt(111) electrode was observed. A temperature-dependent frequency shift of the absorption bands of HSO₄⁻ was also observed on both Pt(1 1 1) and Au(1 1 1) electrodes in the potential region where a √3×√7 structure evolved. Modelling experiments in ultrahigh vacuum revealed that ordering of the overlayer water molecules played an important role in the frequency of the absorption bands of HSO₄⁻.     

A “vertex electron pair” scheme (VEPS) for describing the skeletal electron distribution in borane-type clusters

A predominantly localized electron pair scheme is outlined for describing the electron distribution and bonding in closo borane anions B_nH_n²⁻ and related electron deficient deltahedral clusters, in which a skeletal electron pair is assigned to each vertex, one pair being regarded as delocalized just inside the roughly spherical surface on which the skeletal atoms lie. The scheme gives a clearer picture of the electron distribution than is conveyed by resonating 2- and 3-centre bonds in the polyhedron edges and faces, and allows the bond orders of the polyhedron edge links to be calculated readily. The consequence of formal removal of BH²⁺ units from closo species B_nH_n²⁻ to generate nido species B_n−1H_n−1⁴⁻ and arachno species B_n−2H_n−2⁶⁻ is explored, and seen to allow rationalization of two features of such deltahedral-fragment clusters: (i) why a high-connectivity vertex is left vacant and (ii) why the frontier orbitals of such species concentrate electronic charge around their open faces. Moreover, in the case of D_4‘h B₄H₄⁶⁻ (cf. C₄H₄²⁻) and D_5h B₅H₅⁶⁻ (cf. C₅H₅⁻), the approach leads directly to the familiar picture for aromatic ring systems in which the highest filled, doubly degenerate π-bonding molecular orbital concentrates electronic charge in rings above and below the polygon on which the skeletal nuclei lie. It also leads to the expectation that arachno clusters with non-adjacent vacant vertices will be more stable than those with adjacent vacant vertices.     

Are excimers formed along with hydrated electrons in the UV excitation of cyanocuprate(I) ions in aqueous solution?

The three cyanocuprate(I) complexes, Cu(CN)₂⁻, Cu(CN)₃²⁻, and Cu(CN)₄³⁻, photoeject electrons with high efficiency when excited in aqueous solution by 266 nm laser pulses of 7 ns duration with quantum yields of 0.37±0.06, 0.224±0.021, and 0.240±0.005, for Cu(CN)₂⁻ (at 2 M ionic strength), Cu(CN)₃²⁻, and Cu(CN)₄³⁻ (both measured at 1 M ionic strength). Along with hydrated electrons, two transient intermediates, absorbing at 460 and 340 nm, respectively, form consecutively after excitation through bimolecular reactions with ground-state Cu(I) in solutions of Cu(CN)₂⁻, and Cu(CN)₃²⁻, but not in Cu(CN)₄³⁻. All photoprocesses are essentially monophotonic. A mechanism is proposed that suggests the formation of a dinuclear excited-state complex such as an excimer.     

Improvement of the performance of single-column ion chromatography by computerized detector signal processing and correlation chromatography

The performance of medium-quality ion chromatographic equipment was improved by using pseudo-random sample intoduction correlation chromatography (CC). The importance of the digital preprocessing of the detector signal prior to decorrelation was demonstrated for realization of the multiplex advantage of the CC method. The detection limits obtained for single-column ion chromatography using conductivity were 0.1, 0.12, and 0.17 ppm for Cl⁻, NO₃⁻ and SO₄²⁻ ions, respectively. Using the same apparatus without CC the detection limits are in the range 1–3 ppm.     

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.     

Ab initio studies on the electronic structures of certain 10π-electron six-membered ring compounds

By using ab initio methods of all-electron or effective core potential calculations, the electronic structures and the possible aromaticity of some 10π-electron systems, C₆H₆⁴⁻ (1), N₆⁴⁻ (2), P₆⁴⁻ (3), S₆²⁻ (4), Te₆²⁻ (5) and S₃N₃⁻ (6), have been studied at the SCF levels using 4-31G//4-31G and 6-31G^*//6-31G^* basis sets. The bonding characteristics of these systems are analysed in terms of the canonical molecular orbital and the Foster-Boys localized molecular orbital results. The application of the second-order Jahn-Teller theorem to the stability of these diamagnetical planar species is presented.     

Acid-rain monitoring in East Asia with a portable-type ion-exclusion–cation-exchange chromatographic analyzer

A monitoring system consisting of a portable-type conductimetric ion-exclusion–cation-exchange chromatographic (CEC) analyzer and a meteorological satellite data analyzer has been investigated for the evaluation of the effects of acid precipitation on natural and urban environments in East Asia. The portable ion-exclusion–CEC analyzer uses a polymethacrylate-based weakly acidic cation-exchange resin column in the H⁺-form and a weak-acid eluent (tartaric acid–methanol–water) and is applied for the simultaneous determination of anions (SO₄²⁻, NO₃⁻, and Cl⁻) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) in precipitation transported from mainland China to central Japan, as mapped by the meteorological satellite data analyzer. Linear calibration graphs of peak area versus concentration for anions and cations were observed in the concentration range 0–1.0 mM for the anions and 0–0.5 mM for the cations. Detection limits at a signal-to-noise ratio of 3 were in the range 5.18–12.1 ppb for the anions and 6.58–16.5 ppb for the cations. The practical utility of this monitoring system is presented.     

Decolorization and mineralization of textile dyes at solution bulk by heterogeneous nanophotocatalysis using immobilized nanoparticles of titanium dioxide

Nanophotocatalysis using nanostructured semiconductors constitute one of the emerging technologies for destructive oxidation of organics such as dyes. This paper deals with the decolorization and mineralization of reactive dyes by heterogeneous nanophotocatalysis using an immobilized TiO₂ nanoparticle photocatalytic reactor. A simple and effective method was used to immobilization of titanium dioxide nanoparticles. Reactive Orange 107 (RO 107, sulphatoethylsulphonyl reactive dye) and Reactive Red 152 (RR 152, monochlorotriazine reactive dye) were used as model compounds. UV–vis and ion chromatography (IC) analyses were employed to obtain the details of the photocatalytic degradation of the selected dyes. The effects of operational parameters such as H₂O₂, dye concentration, anions (NO₃⁻, Cl⁻, SO₄²⁻, HCO₃⁻ and CO₃²⁻) and pH were investigated. Formate, acetate and oxalate anions were detected as dominant aliphatic intermediates where, they were further oxidized slowly to CO₂. Nitrate, sulfate and chloride anions were detected as the photocatalytic mineralization of RO 107 and RR 152. Kinetics analysis indicates that the photocatalytic decolorization rates can usually be approximated zero-order model for RO 107 and first-order model for RR 152 dyes. Results show that the photocatalytic process occurred at solution bulk and the employment of optimal operational parameters may lead to complete decolorization and mineralization of dye solutions.     

Peroxidase immobilized on Amberlite IRA-743 resin for on-line spectrophotometric detection of hydrogen peroxide in rainwater

The importance of atmospheric hydrogen peroxide (H₂O₂) in the oxidation of SO₂ and other compounds has been well established. A spectrophotometric method for the determination of hydrogen peroxide in rainwater is proposed. This method is based on selective oxidation of hydrogen peroxide using an on-line tubular reactor containing peroxidase immobilized on Amberlite IRA-743 resin. The hydrogen peroxide in the presence of phenol, 4-aminoantipyrine and peroxidase, produces a red compound (λ = 505 nm). Beer's law is obeyed in a concentration range of 1–100 μmol l⁻¹ hydrogen peroxide with an excellent correlation coefficient (r = 0.9991), at pH 7.0, with a relative standard deviation (R.S.D.) <2%. The detection limit of the method is 0.7 μmol l⁻¹ (4.8 ng of H₂O₂ in a 200 μl sample). Measurements of hydrogen peroxide in rain samples were carried out over the period from November 2003 to January 2005, in the central area of the Juiz de Fora city, Brazil. The concentration of H₂O₂ varied from values lower than the detection limit to 92.5 μmol l⁻¹. The effects of the presence of nonseasalt (NSS) SO₄²⁻, NO₃⁻ and H⁺ in the concentration of hydrogen peroxide in the rainwater had been evaluated. The average concentrations of H₂O₂, NO₃⁻, NSS SO₄²⁻ and SO₄²⁻ are 23.4, 18.9, 7.9 and 10.3 μmol l⁻¹, respectively. The pH values for 82% of the collected samples are greater than 5.0. The spectrophotometeric method developed in this work that uses enzyme immobilized on the resin ion-exchange compared with the amperometric method did not present any significant difference in the results.