Possibilities for speciation of Al-citrate and other negatively charged Al complexes by anion-exchange FPLC-ICP-AES

An anion-exchange fast protein liquid chromatographic-inductively coupled plasma atomic emission spectrometric procedure (FPLC-ICP-AES) was developed for speciation of Al-citrate and other negatively charged Al complexes. FPLC separations were carried out on a Mono Q HR 5/5 strong anion-exchange FPLC column over a pH range from 3.5 to 11.0. An aqueous-NaNO(3) (4 mol dm(-3)) linear gradient elution was applied over 10 min for separation of a particular Al species. The separated Al species were determined in 0.5 cm(3) eluate fractions ;off line' by ICP-AES. Under optimal analytical procedures Al-citrate was separated from Al-oxalate and Al-EDTA in a neutral pH range. Good reproducibility of the FPLC-ICP-AES procedure was obtained for determination of a particular Al species at optimal measurement conditions (RSD +/-2%). Al(3+) and neutral Al-citrate species were strongly adsorbed on the column resin and did not interfere with the separation of negatively charged Al complexes. Al(OH)(4)(-) species were separated from Al-citrate in an alkaline pH region, but quantitatively determined only at a pH of 11.0. The distribution of Al species over a pH range from 3.5 to 11.0 agreed with the reported calculated data. The limit of detection (3sigma basis) for separated Al species was 0.1 mug cm(-3).     

New method for speciation analysis of aluminium fluoride complexes by HPLC-FAAS hyphenated technique

Speciation analysis of aluminium in the presented system of HPLC-FAAS hyphenated technique lasts 4 min. Using the bifunctional column in model analysis and using the calculation methods for modelling using the Mineql program enabled the authors to presume that particular forms will be subjected to elution in the following order: (1) AlF₂⁺ and AlF₄⁻, (2) AlF²⁺ and AlF₃⁰ and (3) Al³⁺. Based on the obtained results for model solutions, the presented method enables the determination of aluminium fluoride complexes and Al³⁺ speciation form. The study compares the tendency of occurrence variability of aluminium fluoride complexes and Al³⁺ form, determined based on the results obtained using the HPLC-FAAS hyphenated technique with the trend defined based on the Mineql program calculation method. The method was successfully applied to soil samples.     

Speciation of trace amounts of aluminium in percolating water of forest soil by online coupling HPLC-ICP-MS

Procedures were developed for the speciation of trace amounts of aluminium present in percolating water of forest soil by online coupling of different chromatographic separation methods to an ICP-MS detection system. Inorganic and organic aluminium species were fractionated on a cation exchange column IONPAC CG12 (10-32). Phytotoxic polymeric aluminium hydroxides, as e.g. Al₁₃ (AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺), were determined using pyrocatechol violet (PCV) as a species dependant complexing reagent prior to the cation exchange step. Size fractionation of the organic aluminium species was obtained by size exclusion chromatography using the columns Superdex-75-HR 10/30 and Superdex-Peptide-HR 10/30. Validation of the speciation procedures proved that online coupling HPLC to the element selective and sensitive ICP-MS detection system leads to low detection limits of 0.3–0.6 μg/L and high precision and reproducibility (1.2–3.5%) of the speciation procedures. Speciation data determined for aluminium in a percolating water of the Zierenberg catchment are given.     

Speciation of prehydrolyzed Al salt coagulants with electrospray ionization time-of-flight mass spectrometry and Al NMR spectroscopy

Based on the speciation results of the most two concerned coagulant component (i.e., monomer and Keggin-Al₁₃), Al species in polymeric Al salt coagulants were fully investigated with the combination of electrospray ionization time-of-flight mass spectrometry and ²⁷Al NMR spectroscopy. Keggin-Al₁₃⁷⁺ could transform into Al₁₃ⁿ⁺ (n = 1-3) by dehydrogen reaction without destroying the Keggin structure in mass spectrometer. There exist differences in the intensity and the observed sequence of the Al₁₃ⁿ⁺ (n = 1-3) species in the mass spectra of polymeric Al coagulants. Several other polymers (i.e., Al₁₉³⁺, Al₂₀³⁺ and Al₁₆ⁿ⁺, n = 1-3) might also be formed by the decomposition and repolymerization of Keggin-Al₁₃⁷⁺. Like monomeric Al salt coagulant, species in polymeric Al coagulants with low basicity were mainly detected as low polymers with mono-charge in mass spectrometry. With the increase of basicity, the dominant species often transform into high polymers with higher charges and fewer categories. The Al₁₃³⁺ species detected in monomeric Al coagulant should have octahedral structure and be formed by self hydrolysis, which is different with the species detected in purified Al₁₃ coagulant. On the whole, the detected species in mass spectrometry could roughly represent their dissolution status in original solutions and could also be used to explain the difference of their coagulation performance in water treatment process.     

Speciation analysis of aluminium and aluminium fluoride complexes by HPIC-UVVIS

The study presents a new analytical method for speciation analysis in fractionation of aluminium fluoride complexes and free Al³⁺ in soil samples. Aluminium speciation was studied in model solutions and soil extract samples by means of high performance ion chromatography (HPIC) with UV-VIS detection using post-column reaction with tiron for the separation and detection of aluminium fluoride complex and Al³⁺ forms during one analysis. The paper presents particular stages of the chromatographic process optimization involving selecting the appropriate eluent strength, type of elution or concentration and quantity of derivatization reagent. HPIC was performed on a bifunctional analytical column Dionex IonPac CS5A. The use of gradient elution and the eluents A: 1 M NH₄Cl and B: water acidified to pH of eluent phase, enabled full separation of fluoride aluminium forms as AlF₂⁺, AlF₃⁰, AlF₄⁻ (first signal), AlF²⁺ (second signal) and form Al³⁺ in a single analytical procedure. The proposed new method HPIC-UVVIS was applied successfully in the quantitative and qualitative analysis of soil samples.     

Speciation of aluminium fluoride complexes and Al in soils from the vicinity of an aluminium smelter plant by hyphenated High Performance Ion Chromatography Flame Atomic Absorption Spectrometry technique

The paper presents a new tool for the determination of inorganic speciation forms of aluminium: AlF_n^{(3 − n)+}, and Al³⁺ by means of the HPIC-FAAS. The proposed method has been successfully used for speciation analysis (qualitative and quantitative) of inorganic aluminium forms AlF_n^{(3 − n)+} in soil samples. In order to isolate the most environmentally available fraction, 5 g of the sample was collected and extracted in deionised water (water soluble fraction) for 1 h using a magnetic stirrer. The determinations in a hyphenated technique system were performed for a number of prepared water extracts. Concentration determinations of particular aluminium forms were performed based on model studies and real samples. The separation of Al species with nominal charge of + 1, + 2, and + 3 required a run time of less than 4 min during a single analysis. Based on the analysis of water extracts of soil, it was obtained that aluminium forms elute in the following order: 1PA (first signal) — AlF₂⁺ and/or AlF₄⁻; 2PA (second signal) — AlF²⁺ and/or AlF₃⁰; 3PA (third signal) — Al³⁺. In order to confirm the occurrence of these forms a simulation using the Mineql program was conducted. The details of speciation analysis of aluminium fluoride forms by means of an HPIC-FAAS instrument equipped are presented. Interpretation of the speciation analysis of the water soluble fraction of soil samples is proposed, based on the separation during chromatographic run and calculated data by Mineql.     

Potentiometric Study of the Effect of Sodium Dodecylsulfate and Dioxane on the Hydrolysis of the Aluminum(III) Ion

Hydrolytic equilibria of the aluminum(III) ion were studied in the presence of a surfactant, sodium n-dodecylsulfate (SDS) and, separately, in mixed water + dioxane and water + dioxane + surfactant media at 298.15 K, by using potentiometric measurements with a glass electrode. The concentration of SDS was between 1.25 and 25.0 mmol-dm⁻³, whereas the volume percent of dioxane was varied from 10 to 50. The supporting strong electrolyte was 0.1 mol-dm⁻³ LiCl. A general least-squares treatment of the data indicates the formation of mononuclear hydrolytic complexes of the form Al(OH)_m^{3 − m} (m = 1–3) at all studied compositions. At lower concentrations of SDS (≤ 12.5 mmol-dm⁻³) it was necessary to include polynuclear hydrolytic complexes in the hydrolytic model. On increasing the concentration of SDS, the formation of polynuclear complexes is suppressed, and at the SDS concentration of 25.0 mmol-dm⁻³, only Al(OH)²⁺ and Al(OH)₂⁺ are observed in solution. At lower volume percentages of dioxane, the speciation involved polynuclear complexes in addition to mononuclear complexes. At dioxane concentrations higher than 20 vol% only mononuclear complexes are formed. The simultaneous presence of the SDS and dioxane as ionic medium modifiers produces only the mononuclear complexes Al(OH)²⁺ and Al(OH)₂⁺, which have significantly higher stability constants than in the pure ionic medium.     

Effects of Al(III) speciation on cell membranes and molecular models

Aluminum, a very abundant metal, might play an important role in several pathologies which could be related to its interactions with cell membranes. Although the effects of Al(III) on biological membranes have been extensively described, direct information concerning the molecular basis of its biological activity is rather scarce. One reason for this lack of molecular information is the ill-defined chemical speciation of the metal compounds utilized in toxicological experimental protocols. Another is the complex molecular structure of cell membranes. For this reason, molecular models consisting in phospholipid bilayers are commonly used. In this review the interaction of four Al(III) compounds with phospholipid bilayers built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) and their effects on ion channels present in isolated toad skins are discussed. The aluminum compounds are Al(acac)₃, AlCl₃, AlF₃ and the Al-citrate complex [K₅Al(C₆H₄O₇)₂]. It is concluded that they interact with and produce different structural and functional effects on the model and biological membranes. X-ray diffraction revealed that AlCl₃ (1 mM) induced the most damaging effects to both DMPC and DMPE bilayers whereas the Al-citrate complex caused only slight perturbation, the effects of Al(acac)₃ and AlF₃ being intermediate. The inhibitory effects on the isolated skin, in descending order, were (100 μM): AlCl₃, possibly by indirect and direct inactivation of Na⁺ channels and/or perturbation of an ATPase; AlF₃, by direct inactivation of the Na⁺ channel and mild ATPase inhibition; Al-citrate, by decrease of Na⁺ permeability, and lastly, Al(acac)₃, which decreased Na⁺ transport only at far higher concentration (250 μM).     

Simultaneous determination of aluminium,aluminium fluoride complexes and iron in groundwater samples by new HPLC–UVVIS method

The paper presents the application of the new HPLC–UVVIS method used in speciation analysis of aluminium form Al³⁺, aluminium complexes with fluorides and iron in groundwater samples. Based on the obtained results of groundwater samples analysis, the separation of iron in the retention time ≈ 3.7, was obtained. The conditions of the occurrence of particular aluminium forms based on the speciation analysis and modeling in the Mineql program were presented and confirmed. The influence of pH and ligand concentration on forming complexes was shown. The preliminary study of aluminium complexes with sulfates based on model solutions did not allow for the separation of the above complexes in presented analytical system. The paper presents the possible types of transformation of aluminium hydroxy forms and aluminium sulfate complexes by the reaction of the sample with mobile phase. An indirect method for the determination of aluminium in the form of aluminium sulfate was proposed. The new method was successfully applied in the determination of the following aluminium forms: Al³⁺, AlF₂⁺, AlF₃⁰, AlF₄^?, AlF²⁺ and Fe³⁺.     

Preconcentration and speciation of inorganic and methyl mercury in waters using polyaniline and gold trap-CVAAS

Applicability of polyaniline (PANI) has been investigated for the preconcentration and speciation of inorganic mercury (Hg²⁺) and methyl mercury (CH₃Hg⁺) in various waters (ground, lake and sea waters). Preliminary experiments (batch) with powdered PANI for the quantitative removal of both Hg²⁺ and CH₃Hg⁺ showed that the retention of Hg²⁺ was almost independent of pH while a pH dependent trend from pH 1 to 12 was seen for CH₃Hg⁺ with maximum retention at pH > 5. Time dependence batch studies showed that a contact time of 10 min was sufficient to reach equilibrium. The K_d values were found to be ∼8 × 10⁴ and ∼7 × 10³ for Hg²⁺ and CH₃Hg⁺, respectively.Subsequently column experiments were carried out with PANI and the separation of the species was carried out by selective and sequential elution with 0.3% HCl for CH₃Hg⁺ and 0.3% HCl-0.02% thiourea for Hg²⁺. This was then followed by further pre-concentration of mercury on a gold trap and its determination by CVAAS. The uptake efficiency studies showed that the PANI column was able to accumulate up to 100 mg Hg²⁺/g and 2.5 mg CH₃Hg⁺/g. This method allows both preconcentration and speciation of mercury with preconcentration factors around 120 and 60 for Hg²⁺ and CH₃Hg⁺, respectively. The interfering effects of various foreign substances on the retention of mercury were investigated.     

Column chromatographic speciation of chromium for Cr(VI) and several species of Cr(III)

Summary Chromium can be present in aqueous solution as Cr(VI) or in monomeric, dimeric, trimeric and higher polymeric forms of Cr(III). Many monomeric forms of Cr(III) are possible, with the water molecules of Cr(H₂O) ₆ ³⁺ substituted by anionic or neutral species. This proliferation of Cr(III) species makes the complete speciation of chromium a continuing challenge to the analyst. A simple and effective cation exchange procedure for the separation of various of these species uses a small glass column containing 1 mL of pre-treated cation exchange resin (Na⁺ form). Stepwise elution with solutions of perchloric acid, Ca²⁺ (pH=2) and La³⁺ (pH=2) separates Cr(VI) and seven Cr(III) species from CrX₃ to tetramer. Radiometric (Cr-51), spectrophotometric and other detection methods can be employed; the use of radiochromium gives the lowest detection limit.     

The reaction of alf3 solution with aluminium hydroxide and some reactions of the aluminium hydroxyfluoride obtained

AlF₃ solution (150 g/l) reacts with Al(OH)₃ in the m.ratio 2:1 in excess of ca. 115°C to produce Al(OH,F)₃.H₂O with an F/Al at. ratio > 2. At lower temperatures, e.g. 110°C, or at higher reactants ratios, e.g. 3-11, formation of Al(OH,F)₃.H₂O may be accompanied by crystallization of AlF₃-hydrates as AlF₃.3H₂O and/or /gb-AlF₃.H₂O. When crystallization of β - AlF₃.H₂O occurs to a greater extent, Al(OH,F)₃.H₂O may vary in its F/Al at.ratio from ca. 2.5 to 1, during the reaction.Al(OH)F₂.H₂O reacts readily with NaOH, NaF and NH₄F solutions to give sodium and ammonium cryolite. Reactions with NaHF₂ and H₂SiF₆ were unsuccessful, while with AlF₃ solution an increase of the F/Al ratio in the Al basic fluoride used resulted.     

Investigation of Aluminate Solutions by water activity measurement

Isopiestic measurements were used to determine the change in water activity due to the variation of the aluminium content of alkaline aluminate solutions. This parameter was found suitable to indicate the concentration dependence of the species present in the solution. It was established that the increase of water activity due to the increased aluminium concentration can be attributed to two processes: 1. the coordination of hydroxide ion to aluminium, 2. dimerization connected with the dehydration of the monomeric species. On the basis of the Gibbs-Duhem equation the water activity data gave an indication of the concentration ranges in Which the sodium aluminate solution exists mainly as (I) NaOH + monomeric Al(OH)₄^? and ( H ) NaOH + dimeric Al₂ O(OH)₆ ^2? ions.     

Development of a new analytical method for online simultaneous qualitative determination of aluminium (free aluminium ion, aluminium-fluoride complexes) by HPLC-FAAS

The paper presents a novel method for simultaneous online examination of inorganic forms of aluminium: AlF₂⁺, AlF^2+, and Al³⁺ by means of the high performance liquid chromatography hyphenated with a detection by the atomic absorption spectrometry with flame atomization (HPLC-FAAS) without post-column reaction. The application of optimization procedure conditions of chromatographic separation of inorganic forms of aluminium was achieved by the analytical column IonPac CS5A (Dionex) with guard column IonPac CG5A (Dionex) and an aqueous ammonium chloride mobile phase, at pH about 3 with gradient elution. The separation of Al forms with nominal charge of 1+, 2+, 3+ required a run time of less than 8 min during a single analysis. The proposed method has been successfully used for the examination of aluminium forms formation AlF_n⁽³⁻ⁿ⁾⁺ in environmental samples.     

Extreme Differences in the Interactions of `Bare' Fe+ and Fe2+ with Hydrogen Peroxide: Fenton Chemistry in the Gas Phase

The interaction of bare iron mono‐ and dications with hydrogen peroxide in the gas phase is studied by ab initio calculations employing the B3LYP/6‐311+G* level of theory. For the monocation, the quartet and sextet coordination complexes Fe(H₂O₂) are high‐energy isomers that easily interconvert to the more stable iron dihydroxide monocation Fe(OH) and hydrated iron oxide (H₂O)FeO⁺ (quartet) or dissociate into FeOH⁺+OH^. (sextet). On the dication surface, however, the order of stabilities is reversed in that Fe(H₂O₂)²⁺ (quintet) corresponds to the most stable doubly charged species, while the formal Fe^IV compounds Fe(OH) and (H₂O)FeO²⁺ are higher in energy.     

Spectroscopic investigation of uranium sorption on soil surface using X-ray photoelectron spectroscopy

A study was carried out to understand the sorption of uranium (U) onto soil surface and identify the species of U on soil surface using X-Ray Photoelectron Spectroscopy (XPS). For the study soil was amended with uranyl nitrate and surface speciation study was carried out by investigating the energy region for U in spectrum. Analysis of spectrum revealed that U is present in U(VI) state. Deconvolution of XPS spectrum of U(VI) sorbed on soil surface revealed that U(VI) species such as, UO₂ ²⁺ and (UO₂)_x(OH) _y ^(2x?y)+ form complex with silanol, aluminol and goethite sites. The possible surface complexation is: ≡Al(OH)₂UO₂ ²⁺, ≡SiO₂UO₂, ≡SiO₂(UO₂)₃(OH)₅ and ≡Fe(OH)₂UO₂.     

Functionalized SBA-15 mesoporous silica in ion chromatography of alkali,alkaline earths,ammonium and transition metal ions

The retention properties of a SBA-15 mesoporous silica functionalized with –(CH₂)₃COOH groups, synthesized by a co-condensation route, were investigated for the ion chromatography of different cationic species. A systematic study on the effect of different eluent compositions containing non-complexing (methanesulfonic acid) or complexing (oxalic or pyridine-2,6-dicarboxylic acids) eluents, in the presence of organic modifiers (CH₃CN, CH₃OH, CH₃NH₂) on the retention of cations (Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺, NH₄⁺, Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Pb²⁺, Fe³⁺) chosen as model analytes and for their environmental importance, allowed us to elucidate the mechanisms (cation-exchange or complexation) involved in the retention on the SBA-15 phase. For the first time separations of cations on SBA-15 based stationary phases are investigated, providing the basis for further development of mesoporous silica chemistry for in-flow ion-exchange applications.     

The adsorption of CaOH+ on (001) basal and (010) edge surface of Na‐montmorillonite: a DFT study

Ca²⁺ cations were generally added to facilitate the coagulation of stable fine clay mineral dispersion due to the specific adsorption of their first hydrolysis CaOH⁺ species at pH near 10. The adsorption of CaOH⁺ on dry and hydrated (001) basal surface and (010) surface of Na‐montmorillonite was investigated by using density functional theory method combined with the periodic slab model method. The adsorption energies and geometries, Mulliken charge, electron density difference, and density of state were presented and discussed. It was found that the adsorption energy of CaOH⁺ on (010) edge surface of Na‐montmorillonite (?328.8 kJ/mol) was much larger than that (?126.9 kJ/mol) on (001) basal surface. The presence of waters could increase the adsorption energy of CaOH⁺ on (001) surface but affect that on (010) surface slightly. The protons in Si–OH and Al–OH₂ groups as well as the OH₂ ligands in Al–OH₂ group on (010) edge surface were easily dissociated and coordinated to CaOH⁺ to form new waters. CaOH⁺ was the most steady adsorption species among CaOH⁺, Ca²⁺ cation, and H₂O molecule on both (001) and (010) surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

Potentiometric Study of Aluminium-Fluoride Complexation Equilibria and Definition of the Thermodynamic Model

Complexation constants of the Al³⁺/F⁻ system were determined at different ionic strengths in a NaClO₄ (1.0, 2.0 and 3.0 mol⋅dm⁻³) ionic medium by means of a potentiometry using two electrode systems: an ion fluoride selective electrode as well as a glass electrode. All the experimentation was performed at 25 °C. The main species in the complexation equilibria were determined as AlF²⁺, AlF₂⁺, AlF₃⁰, AlF₄⁻, AlF₅²⁻ and AlF₆³⁻. The differences found in the complexation constants for the ionic strength considered were explained by the different behavior of the interaction parameters for the AlF _n ³⁻ⁿ species. These parameters were calculated using the Modified Bromley’s Methodology (MBM). The corresponding thermodynamic quantities were also determined. From all the results obtained, it can be concluded that pH, fluoride concentration and ionic strength influenced the distribution of the fluoride-aluminium complexes.     

Speciation and NMR Spectrometric Studies of Interaction of Di- and Tri-organotin(IV) Moieties with 5′-Guanosine Monophosphate and Guanosine in Aqueous Solution

Potentiometric studies of the interaction of (Me₂Sn)²⁺ and (Me₃Sn)⁺ with 5′-guanosine monophosphate [(5′-HGMP)^2?, abbreviated as (HL-1)^2?] and guanosine [(HGUO), abbreviated as (HL-2)] in aqueous solution (I = 0.1 mol·dm^?3 KNO₃, 298.15 ± 0.1 K) were performed, and the speciation of various complex species was evaluated as a function of pH. The species that exist at physiological pH ~7.0 are Me₂Sn(HL-1)/[Me₂Sn(HL-2)]²⁺ (87.0/88.8 %), [Me₂Sn(HL-1)(OH)]^?/[Me₂Sn(HL-2)(OH)]⁺ (3.0/0 %) and [Me₂Sn(HL-1H_?1)]/[Me₂Sn(HL-2H_?1)]²⁺ (9.4/6.6 %) for 1:1 dimethyltin(IV):5′-guanosine monophosphate/dimethyltin(IV): guanosine systems, whereas for the corresponding 1:2 systems, the species are Me₂Sn(HL-1)/[Me₂Sn(HL-2)]²⁺ (44.0/92.0 %), [Me₂Sn(HL-1H_?1)]/[Me₂Sn(HL-2H_?1)]²⁺ (5.0/6.0 %), Me₂Sn(OH)₂ (49.0/0 %), [Me₂Sn(HL-1)(OH)]^?/[Me₂Sn(HL-2)(OH)]⁺ (1.5/2.0 %), and [Me₂Sn(OH)]⁺ (1.0/0 %). For 1:1 trimethyltin(IV):5′-guanosine monophosphate/trimethyltin(IV):guanosine systems, only [Me₃Sn(HL-1)]^?/[Me₃Sn(HL-2)]⁺ (99.9 %) are found at pH = 7.0, whereas for 1:2 systems, [Me₃Sn(HL-1)]^?/[Me₃Sn(HL-2)]⁺ (49.8/100 %), Me₃Sn(OH) (15.0/0 %) and [Me₃Sn(HL-1)(OH)]^2?/Me₃Sn(HL-2)(OH) (0.2/0 %) are the species found. No polymeric species were detected. Beyond pH = 8.0, significant amounts of [Me₂Sn(OH)]⁺, Me₂Sn(OH)₂, [Me₂Sn(OH)₃]^? and Me₃Sn(OH) are formed. Multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR studies at different pHs indicated a distorted octahedral geometry for the species Me₂Sn(HL-1)/[Me₂Sn(HL-2)]²⁺ in dimethyltin(IV)-(HL-1)^2?/(HL-2) systems and a distorted trigonal bipyramidal/distorted tetrahedral geometry for the species [Me₃Sn(HL-1)]^?/[Me₃Sn(HL-2)]⁺ in trimethyltin(IV)-(HL-1)^2?/(HL-2) systems.