Speciation of aluminium(III) in natural waters using differential pulse voltammetry with a pyrocatechol violet-modified electrode

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different AlIII forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm(-3) NaOAc-HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20 mol dm(-3) NH3.H2O-NH4Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester AlIII from AlIII-natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll's 8-hydroxyquinoline extraction-ion exchange method.     

Resonance Rayleigh scattering determination of trace amounts of Al in natural waters and biological samples based on the formation of an Al(III)-morin-surfactant complex

A novel method for the determination of trace amounts of Al(III) based on resonance Rayleigh scattering (RRS) has been developed. In the presence of some surfactants, Al(III) can react with morin and form an Al(III)-morin-surfactant complex, which results in the enhancement of RRS intensity and the appearance of the corresponding RRS spectral characteristics. Their maximum scatter peaks are at 476 nm for the cetyltrimethylammonium bromide (CTAB) system, 489 nm for the cetylpyridinium chloride (CPC) system, 474 nm for the Triton X-100 system, and 473 nm for the Tween-20 system. The enhanced RRS intensity is directly proportional to the concentration of Al(III). The detection limits are in the range of (0.50-1.2)×10⁻⁷ mol l⁻¹ depending on the surfactant. The characteristics of RRS spectra of the complexes, the optimum conditions of these reactions and the influencing factors have been investigated. The method has high selectivity, and was successfully applied to the determination of Al(III) in natural and biological samples. Furthermore, according to different complexation capacity of Al(III)-morin-CTAB system under two pH conditions, speciation analysis of Al(III) in natural waters was explored. The labile monomeric Al fraction (mainly inorganic Al, Al_i) is determined at acidic pH and the total monomeric Al fraction (Al_a) is determined at alkaline pH. The results are in agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction-ion exchange method.     

Fractionation of aluminum in natural waters by fluorometry based on the competitive complexation

A novel strategy for the speciation of aluminum has been developed by fluorometry using selective analytical reagents under different pH conditions, which is based on the measurement of the complexation ability of Al for analytical reagents and native organic matters. With Eriochrome Blue Black R, labile monomeric Al and total monomeric Al fractions are determined at pH 4.5 and pH 8.0, respectively. With morin only the labile monomeric Al is determined at pH 4.0, while with 8-hydroxyquinoline the total monomeric Al is determined at pH 5.5. So, acid soluble Al fraction is obtained indirectly. This method is successfully applied to the fractionation of Al in natural waters. The results well agree with those obtained by Driscoll’s 8-hydroxyquinoline/cation-exchange protocol. This fluorometric method possesses some advantages such as high sensitivity, easy manipulation, no separation step and less time-consuming.     

Analytical methodologies for aluminium speciation in environmental and biological samples--a review

It is recognized that aluminium (Al) is a potential environmental hazard. Acidic deposition has been linked to increased Al concentrations in natural waters. Elevated levels of Al might have serious consequences for biological communities. Of particular interest is the speciation of Al in aquatic environments, because Al toxicity depends on its forms and concentrations. In this paper, advances in analytical methodologies for Al speciation in environmental and biological samples during the past five years are reviewed. Concerns about the specific problems of Al speciation and highlights of some important methods are elucidated in sections devoted to hybrid techniques (HPLC or FPLC coupled with ET-AAS, ICP-AES, or ICP-MS), flow-injection analysis (FIA), nuclear magnetic resonance (27Al NMR), electrochemical analysis, and computer simulation. More than 130 references are cited.     

Analytical methodologies for aluminium speciation in environmental and biological samples – a review

It is recognized that aluminium (Al) is a potential environmental hazard. Acidic deposition has been linked to increased Al concentrations in natural waters. Elevated levels of Al might have serious consequences for biological communities. Of particular interest is the speciation of Al in aquatic environments, because Al toxicity depends on its forms and concentrations. In this paper, advances in analytical methodologies for Al speciation in environmental and biological samples during the past five years are reviewed. Concerns about the specific problems of Al speciation and highlights of some important methods are elucidated in sections devoted to hybrid techniques (HPLC or FPLC coupled with ET–AAS, ICP– AES, or ICP–MS), flow-injection analysis (FIA), nuclear magnetic resonance (²⁷Al NMR), electrochemical analysis, and computer simulation. More than 130 references are cited.     

Colorimetric determination of aluminium(III) with chrome azurol S and the reactivity of hydrolysed aluminium species

The metallochromic reagent chrome azurol S, when used in hexamine buffer at pH 4.9, reacts rapidly with monomeric and small polymeric forms of aluminium(III) in aged hydrolysed solutions. It is unreactive toward the polymer Al₁₃(OH)⁷⁺₃₂ and colloidal Al(OH)₃ and the hydroxyaluminosilicates, imogolite and allophane. The reagent is appropriate for rapid semi-quantitative analysis of labile aluminium in acid lake waters or acid soils.     

Application of dopamine as an electroactive ligand for the determination of aluminum in biological fluids.

Dopamine (3,4-dihydroxyphenylethylamine, DA) is applied as an electroactive chelant for indirect determination of aluminum (Al) in biological fluids. It is observed that the decrease of the differential pulse voltammetric (DPV) anodic peak current of DA is linear with the increase of Al concentration. Under optimum experimental conditions (pH 8.6, 2.0 x 10(-4) M DA, and 0.03 M NH4Ac-NH3 x H2O buffer solution), two linear ranges, 5.0 x 10(-8) - 4.0 x 10(-7) M and 4.0 x 10(-7) - 7.2 x 10(-6) M Al(III), are obtained. The detection limit of Al is 1.9 x 10(-8) M and the relative standard deviation for 4 x 10(-6) M Al(III) is 3.1% (N = 8). Many biologically active foreign species have been selected for interference. Excellent recoveries and accuracy have been obtained in the measurements of Al in biological samples such as synthetic renal dialysate, Ringer's solution, human whole blood, cerebrospinal fluid of demented patient, and urine of diabetic patient. The methodological principle that Al complexes with DA on the electroactive position result in the depression of electrochemical activities of DA has been verified by comparing both the electrochemical behaviors and the spectroscopic responses like UV-vis and Raman of DA in the presence and in the absence of Al.     

邻苯二酚紫-示波计时电位法测定天然水中不同形态铝

报道邻苯二酚紫-示波计时电位法分别在酸性和碱性条件下直接检测天然水中的无机单核铝和总单核铝浓度。并用该法测定了水样中的总铝,有机单核铝和酸溶态铝,从而实现了天然水中5种Al形态的电化学测定。测定了20多个实际水样,与Driscoll方法进行了对照,结果基本一致。     

酸性媒染紫—示波计时电位法测定天然水不同形态铝

本文报道酸性媒染紫（SVRS）一示波计时电位法测定天然水中不同形态铝。对24个实际水样分别在酸性pH5.2测定了无机单核铝Ali和碱性pH8.8底液中测定总单核铝Ala,有机单核铝Al0-Ala-Alio同时还应用该法测定了酸化水样中总铝AlT,酸溶态铝AlT=AlT-Ala,从而实现了水样中五种形态铝的电化学测定,测定值与Driscoll方法进行了比较对照,结果基本一致。本法特点为：简便快捷,灵敏准确,可以直接测定与铝毒性密切相关的无机单核铝Ali,无需分离步骤,水样用量小,适用于大批量天然水样中Al形态的快速分析。     

铬蓝黑R-示波计时电位法快速测定天然水中不同形态的铝浓度

本文报道铬蓝黑 R-示波计时电位法快速测定天然水中不同形态的铝。在 0 .5mol/L 乙酸 -乙酸铵 - 1× 1 0 - 3mol/L铬蓝黑 R( p H4.6)底液中 ,铝 -铬蓝黑 R铬合物在 - 0 .80 V电位处产生灵敏切口 ,切口深度与铝浓度成正比 ,线性范围为 8× 1 0 - 7～6× 1 0 - 5mol/L,检测下限为 6× 1 0 - 7mol/L,相对标准偏差为 4.8% ( n=1 0 ,4× 1 0 - 5mol/L Al)。应用该法测定了天然水中不同形态的铝浓度 ,并同 Driscoll的 MIBK-GF/AAS法进行了比较 ,结果基本一致     

Synthetic and structural carboxylate chemistry of neurotoxic aluminum in relevance to human diseases

The contact of Al(III) with biological components in human physiology has increased significantly over the years, due to a number of factors, prominent among which stands the rapid acidification of the environment and the concomitant introduction of that abundant metal ion in human biological fluids. As a result, pathophysiological aberrations in humans have arisen due to Al(III) (neuro)toxicity. Among the efforts targeting the elucidation of the factors responsible for Al(III) toxicity is the exploration of the requisite Al(III)-carboxylate chemistry in aqueous media, and its relevance to soluble, potentially bioavailable species capable of exerting toxic effects. A detailed synthetic, structural, and spectroscopic account of the Al(III)-carboxylate complexes, purported to exist as components in aqueous Al(III)-carboxylic acid speciation, is presented. The structures described are classified as mononuclear, dinuclear, trinuclear, tetranuclear, and polynuclear species, arising from various aqueous and non-aqueous Al(III)-carboxylate ligand reactions. Moreover, the solution chemistry and kinetic behavior of the so far reported complexes is given, with the specific aim of comparing their solid state and solution chemical and structural properties. In this sense, a comprehensive picture on the Al(III) speciation, in the presence of various physiological or biologically relevant carboxylate ligands, appears to emerge, which is expected to contribute to the understanding of Al(III) (neuro)toxicity and its consequence(s) in a multitude of human diseases. Carboxylate containing low and high molecular mass components stand prominent in their chemical preference to react with Al(III) in biological fluids. In this context, factors considered to influence the aqueous low molecular mass Al(III)-carboxylate chemistry, thus affecting the solubility and possibly the bioavailability of the resulting species, are discussed as potential research links to the ultimate manifestation of Al(III) toxicity at the cellular level.     

Direct Determination of Labile Monomeric Aluminum in Natural Waters By A.C. Oscillopolarography in the Presence of Rubeanic Acid

ABSTRACT

A simple and sensitive electrochemical method for the direct determination of labile (monomeric inorganic Al speciation) Al concentration in natural waters is developed in this paper. It is based on the use of a.c. oscillopolarography in the presence of rubeanic acid (RA). The optimal experimental conditions are: 1 mol/L NaAc-HAc buffer (pH 5.4) and a RA concentration of 6x10^?4 mol/L. The response is linear over the 2x10^?7 to 2x10^?6 mol/L concentration range. The detection limit is 1x10^?7 mol/L and the relative standard deviation (at the 1.2 x 10^?6 mol/L level) is 5.5%. The method has been applied to the direct determination of labile monomeric Al concentrations in various natural samples. The results were verified by the classic ion exchange method.     

Morin applied in speciation of aluminium in natural waters and biological samples by reversed-phase high-performance liquid chromatography with fluorescence detection

A reversed-phase high-performance liquid chromatographic method with fluorescence detection for the determination of labile monomeric aluminium has been developed through pre-column complexation using morin as the analytical reagent. The highly fluorescent aluminium-morin complex (excitation wavelength 418 nm, emission wavelength 490 nm) was separated on a Spherisorb ODS 2 column with an eluent consisting of 30% methanol and 70% water (pH 1.0 with perchloric acid). The most remarkable point of this protocol was that only the most toxic aluminium species, that is, free aqua-aluminium ion and its monomeric hydroxo complex ions, selectively respond among various aluminium complexes. This strategy has been successfully applied to direct fractionation of the toxic aluminium in natural waters and biological samples without any pretreatment.     

Size and charge fractionation of aqueous aluminium in dilute acidic waters: effects of changes in pH and temperature.

In natural waters, aluminium occurs in different physico-chemical forms, depending on pH, temperature and the presence of inorganic and organic ligands. Conventional methods for fractionation of AI species do not fully succeed in separating monomeric, i.e., low relative molecular mass (Mr) AI species, from polymeric colloidal AI species. In the present work, hollow-fibre ultrafiltration and acid digestion steps are introduced prior to the ordinary Barnes-Driscoll procedure. By this method, a colloidal AI fraction is separated from the particulate fraction, i.e., the fraction that is able to precipitate by the force of gravity. Both the monomeric and colloidal AI fractions are characterized according to Mr and the chemical properties such as hydroxyquinoline-isobutyl methyl ketone-extractability and Amberlite IR-120 cation exchangeability. Changes in pH and/or temperature were found to be critical for the analytical results of AI. By combining size and charge fractionation techniques, increased information concerning AI species in dilute freshwaters was obtained. One important investigation is the presence of high Mr AI species in the operationally defined monomeric AI fractions.     

Differential pulse voltammetric indirect determination of aluminium in drinking waters, blood, urine, hair, and medicament samples using L-dopa under alkaline conditions

The differential pulse voltammetric (DPV) indirect determination of aluminium using L-dopa under alkaline conditions on a glassy carbon working electrode was studied. The proposed method relies on the linear decrease of the DPV anodic peak current of L-dopa with increase in the concentration of aluminium added. Under the optimum experimental conditions (pH 8.5, 0.08 M NH4Cl-NH3.H2O buffer solution, and 4 x 10(-4) M L-dopa), the linear range is 2-18 x 10(-7) M AlIII. The detection limit is 7.6 x 10(-8) M and the relative standard deviation for 8 x 10(-7) M AlIII is 3.5% (n = 8). A number of foreign species were examined as potential interferents. The method was applied to the determination of aluminium in drinking waters, synthetic renal dialysate, sodium chloride injection, sucrafate, hydrothorax, blood, urine and hair samples. The physiological significance is discussed.     

A field aluminium speciation method to study the aluminium hazard in water

The toxicity of aluminium is governed by its bioavailability. Therefore, the speciation of aluminium in drinking water becomes of prime importance to understand its fate and the population exposure, and to develop guidelines for the concentration levels. At Health Canada, a field speciation method has been developed to perform on-site speciation followed by measurement of Al in the laboratory. The following species are generated: 1) total recoverable; 2) total acid-leacheable; 3) total dissolved; 4) dissolved extracted; and 5) dissolved non extracted. The field extractions are performed by percolation through chelation columns, which are later processed in the laboratory. Aluminium determinations can then be performed by numerous methods, such as by Inductively Coupled Plasma Mass Spectrometry (ICPMS), Graphite Furnace Atomic Absorption Spectrometry (GFAAS) or Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Examples of results for raw or treated/ distributed surface waters, as well as for groundwaters, are used to illustrate the validity of the method, and the importance of considering aluminium speciation in characterizing the aluminium hazard in water.     

Speciation of Cr(III) and Cr(VI) in surface waters with a Chelex-100 resin column and their quantitative determination using inductively coupled plasma mass spectrometry and instrumental neutron activation analysis

Inorganic Cr(III) and Cr(VI) have contrasting biological, geochemical and toxicology effects. Cr(III) is considered as an essential species for the proper functioning of living organisms but Cr(VI) is toxic for the biological systems. An off-line speciation method using Chelex-100 has been practiced for speciation to Cr(III) and Cr(VI) from surface waters of rivers. The underlying principal of this separation method is based on the ability of cationic Cr(III) to be retained by the resin Chelex-100 while the anionic Cr(VI) remained in the sample matrices. The efficiency of this technique was improved by studying the effect of resin pH. Quantitative determination using inductively coupled plasma-mass spectrometry (ICP-MS) and instrumental neutron activation analysis (INAA) was carried out after the separation to determine the total Cr and Cr(VI) in the liquid matrices. The precision and the accuracy of the quantitative analysis were evaluated by using standard reference material NRCC CASS-2 Intercomparison of INAA and ICP-MS results were determined. The quantity of inorganic Cr(III) and Cr(VI) in the surface water of rivers in the vicinity of industrial areas was investigated together with the determination of the physical properties of the water rivers during sampling.     

Analysis of Toxic Aluminium Species in Natural Waters

Aluminium is known to be toxic to a wide range of aquatic organisms under certain conditions. Monomeric hydroxy ions have been found to be primarily responsible for aluminium aquatic toxicity.A survey of aluminium toxicity and a brief discussion of speciation schemes are presented. The fast reaction of Al³⁺ with pyrocatechol violet (PCV) followed by spectrophotometric analysis is a frequently used method for aluminium speciation. By using a flow system, one obtains fairly exact and reproducible control of the reaction time, and as a result it provides a direct method of analysis for free aluminium (including inorganic monomeric aluminium).The PCV-method has been adapted for the determination of aluminium in carbonate-rich natural waters using an improved buffering system. Thus it is possible to monitor aluminium concentrations in lake water as well as in pore water of the sediments of eutrophicated hardwater lakes that has been treated with aluminium salts as a restoration measure.     

Electrochemical Formation of Al-Li Alloys by Codeposition of Al and Li from LiCl-KCl-AlF3 Melts at 853 K

The electrochemical behavior of Al(III) ions was studied in molten LiCl-KCl melts on a molybdenum electrode. Cyclic voltammetry, chronopotentiometry and chronoamperometry were used to explore the deposition mechanism of Al and Li. Cyclic voltammetry expriment indicates that under potential deposition(UPD) of lithium on pre-deposited aluminium led to the formation of liquid Al-Li alloys at 853 K. The diffusion coefficient of Al(III) ions at 853 K in LiCl-KCl-AlF₃(1%, mass fraction) melts was determined to be (2.79±0.05)×10^?5 cm²/s. Chronopotentiograms and chronoamperograms demonstrate that the codeposition of Al(III) and Li(I) ions formed Al-Li alloys at cathodic current densities higher than ?0.28 A/cm² or cathodic potentials more negative than ?2.20 V. X-Ray diffraction(XRD) pattern indicates that Al-Li alloys with different phases formed via galvanostatic electrolysis. Inductively coupled plasma(ICP) analyses of the samples obtained by electrolysis show that lithium and aluminium contents of Al-Li alloys could be controlled by AlF₃ concentration and current intensity.     

Kinetics of aluminium fluoride complexation in single- and mixed-ligand systems

The complexation reaction between Al(3+) and fluoride was studied over concentration ranges 2-50muM fluoride, 0.5-500muM aluminium, pH 2.5-5.0 at ionic strength 0.1 and temperatures of 298 and 283 K. The initial rate of formation of AlF(2+) was strongly dependent on pH, reaching a minimum at pH 3, and was considerably slower at the lower temperature. Addition of salicylate increased the reaction rate, probably because of the corresponding increase in the initial concentration of AlOH(2+). These effects of pH, temperature and competing ligands will therefore be critical in determining the composition of acid natural water systems and in particular the speciation of soluble aluminium.