Tool For Speciation Research Articles

Lanthanide–humic substances complexation. I. Experimental evidence for a lanthanide contraction effect

The interaction of the lanthanides (Ln) with humic substances (HS) was investigated with a novel chemical speciation tool, Capillary Electrophoresis-Inductively Coupled Plasma Mass Spectrometry (CE-ICP-MS). By using an EDTA–ligand competition method, a bi-modal species distribution of LnEDTA and LnHS is attained, separated by CE, and detected online by sector field ICP-MS. We quantified the binding of all 14 rare earth elements (REEs), Sc and Y with Suwannee river fulvic acid, Leonardite coal humic acid, and Elliot soil humic acid under environmental conditions (pH 6–9, 0.001–0.1 mol L −1 NaNO 3, 1–1000 nmol L −1 Ln, 10–20 mg L −1 HS). Conditional binding constants for REE–HS interaction ( K c) ranged from 8.9 < log K c < 16.5 under all experimental conditions, and display a lanthanide contraction effect, Δ L K c: a gradual increase in K c from La to Lu by 2–3 orders of magnitude as a function of decreasing ionic radius. HS polyelectrolyte effects cause K c to increase with increasing pH and decreasing ionic strength. Δ L K c increases significantly with increasing pH, and likely with decreasing ionic strength. Based on a strong correlation between Δ L K c values and denticity for organic acids, we suggest that HS form a range of tri- to tetra-dentate complexes under environmental conditions. These results confirm HS to be a strong complexing agent for Ln, and show rigorous experimental evidence for potential REE fractionation by HS complexation.

A Novel Multipurpose Excel Tool for Equilibrium Speciation Based on Newton‐Raphson Method and on a Hybrid Genetic Algorithm

A new algorithm for simulation of chemical equilibria is developed, based on classical Newton-Raphson method applied to mass balance. This tool, named EST (Equilibrium Speciation Tool), is improved by using a robust Genetic Algorithm. In addition, EST works by using Excel spreadsheets and therefore offers the innovation of a great simplicity and versatility. In fact, it allows the users to simulate, or to obtain from experimental data, desired chemical-physical parameters as well as to interact with other available or freely created Excel tools. The reliability of this utility is here proved by comparison with some published data by other authors, concerning both complicated homogeneous and heterogeneous equilibria. In addiction its flexibility is tested computing thermodynamic parameters by using experimental calorimetric data referred to the complex formation of cobalt(II) with a macrocyclic ligand. A brief review and comparison of the relative robustness and quickness of main numerical methods are also reported.

Evaluation of DGT as a metal speciation tool in wastewater

This paper aims to evaluate the performance of the diffusive gradient in thin film technique (DGT) as a speciation tool for metals in wastewater. The validity of metal sampling by DGT in wastewater was checked. DGT was used in parallel with the Daphnia magna acute toxicity test in order to obtain information on the speciation of copper and cadmium in diluted and spiked filtered wastewater (raw and treated) from two treatment plants. Combining the chemical (DGT) and the biological methods ( D. magna toxicity test) allowed metal to be fractionated into inorganic, labile organic and inert organic metal. Copper was mainly found as inert organic complexes, whereas the major part of cadmium was found to be labile organic complexes. The proportion of inert organic copper complexes was higher in the presence of treated wastewater than in raw wastewater. The use of restricted gels in DGT devices discriminated more labile organic cadmium than labile organic copper, indicating that cadmium weak ligands have more complex structures than copper weak ligands. In our experimental conditions (i.e. a high metal to ligand ratio), DGT, even equipped with restricted gels, was able to accumulate labile organic complexes. This result highlights that the ecotoxicological interpretation of DGT measurement should be considered carefully. DGT is a reliable tool to assess the chemical characteristics of metals (i.e. reactivity) in wastewater, but it does not ensure that only inorganic metal is measured.

Scanning transmission X-ray microscopy as a speciation tool for natural organic molecules

Summary A molecular-scale understanding of the basic processes affecting stability and transport behavior of actinide cations, complexes or hydroxide (‘eigencolloid’) species is prerequisite to performance assessment of nuclear waste disposal in geological formations. Depending on their functional group chemistry and macromolecular structure, naturally occurring organic molecules (NOM) possess a high tendency towards actinide complexation reactions. However, the compositional and structural heterogeneity of NOM and mixed aggregates with inorganic phases makes speciation by spectromicroscopy techniques highly desirable. The applicability of Scanning Transmission X-ray Microscopy (STXM) as a speciation tool for the characterization of NOM is demonstrated for a multifunctional natural organic acid (chlorogenic acid), Eu(III)-loaded humic acid (HA) aggregates and Eu(III)-oxo/hydroxide/HA hetero-aggregates. It is shown that in situ probing of HA functional group chemistry down to a spatial resolution &lt;100 nm (i.e., less than femto-liter sampled volumes) is feasible, at the same time revealing morphological details on NOM aggregates and NOM/mineral associations.

Chemical speciation by sequential injection analysis: an overview

The simplicity of the sequential injection (SIA) manifold and its low need for maintenance makes it an ideal tool in speciation. As miniaturization and reduction of reagent consumption are also ultimate goals in chemical sensing, it is useful to review the use of combined injection and programmed flow as a central issue in designing SIA systems with chemical sensors and structurally simplified chemical analysers. This overview gives an insight into the current state, analytical scope and performance characteristics of sequential injection systems as analytical tools for speciation. The suitability of SIA for speciation analysis is illustrated by the methods used in the conduits of sequential injection systems for the chemical conversion of different chemical forms into detectable chemical species. Configurations of the basic sequential injection speciation analysis systems were designed around a multi-syringe-time-based-injection system with one detector, direct and indirect speciation of different forms using a single detector including diode array detection and direct speciation of different forms using multiple detection. Examples showing the use of SIA for the simultaneous determination or speciation of metal ions, inorganic anions and organic compounds are given with some recent results from our research groups.

Voltammetry assisted by multivariate analysis as a tool for speciation of metallothioneins: competitive complexation of alpha- and beta-metallothionein domains with cadmium and zinc.

Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) is applied to voltammetric data obtained in the study of competitive complexation of Zn(II) and Cd(II) by alpha- and beta-domains of metallothionein (MT). The application of MCR-ALS allows the estimation of both the voltammograms and the concentration profiles associated with each electrochemical process. The complexity of the voltammograms obtained in titrations of the alpha- or beta-domains of MT with Cd(II) and later Zn(II) (or vice versa) prevents their direct interpretation using traditional electrochemical methods. But when MCR-ALS is applied, voltammograms can be interpreted rather satisfactorily in both qualitative and quantitative terms. MCR-ALS showed the formation of Cd2Znbeta dom and Cd3Znalpha dom complexes when both metals were competitively added. A method based on the combined use of voltammetry and some chemometric techniques is proposed. It can be useful for the metal speciation of environmentally relevant natural ligands.

Eletroforese capilar acoplada à espectrometria com plasma: uma ferramenta eficiente para a especiação

The most important features of the CE-ICP hyphenation, as well as its advantages and drawbacks as a tool for speciation are discussed. The fundamental principles of capillary electrophoresis and inductively coupled plasma mass spectrometry are also presented. Some applications involving different designs proposed in the literature to couple CE and ICP system for elemental speciation are reviewed.

Molecular tools for speciation and epidemiological studies of Acanthamoeba.

Current diagnostic methods for Acanthamoeba identification rely heavily on light microscopic techniques that do not provide sufficient information about the identification of Acanthamoeba at the species level, thus delaying accurate identification of the infective agent. Here we report the use of polymerase chain reaction (PCR)-based restriction enzyme analyses to detect and speciate Acanthamoeba from both clinical and environmental sources by comparing their restriction endonuclease patterns. Significant diversity was observed between and within morphologically defined Acanthamoeba species. The usefulness of PCR-based assays and other available diagnostic methods is discussed.

Heavy metal content and speciation in groundwater of the Guadiamar river basin

This work presents the conclusions of a speciation study concerning Zn, Cd, Pb and Cu in groundwater from ten wells in the alluvial aquifers of the Guadiamar river, affected by Aznalcollar mine tailing spill (April 1998). The sampling campaign took place in January 2000, almost two years after the mining accident. Four metal fractions were determined: labile metal forms, H + exchangeable metal forms, strongly inert forms (associated with organic and inorganic matter in solution), and forms associated with suspended matter. Total metal concentration in groundwater followed the trend Cd<Pb<Cu<Zn. The speciation study showed that Zn and Cd were present to a great extent in available forms (labile and H + exchangeable), while Pb and Cu were found mostly in the less available forms (strongly inert). These results can illustrate the potential value of the speciation tool for the follow-up of spill-induced pollution in the area.

Trace cobalt speciation in bacteria and at enzymic active sites using emission Mössbauer spectroscopy.

57Co emission Mössbauer spectroscopy (EMS) allows the chemical state of cobalt, as influenced by its coordination environment, to be monitored in biological samples at its physiological (trace) concentrations. To draw attention to EMS as a valuable tool for speciation of cobalt in biocomplexes, the process of cobalt(II) metabolism in cells of the plant growth-promoting rhizobacterium Azospirillum brasilense Sp245 was investigated using EMS of 57CoII-doped bacterial cells. EMS measurements also showed 57CoII-activated glutamine synthetase (GS, a key enzyme of nitrogen metabolism, isolated from this bacterium) to have two different cobalt(II) forms at its active sites, in agreement with data available on other bacterial GSs. Chemical after-effects following electron capture by the nucleus of the parent 57CoII during the 57Co-->57Fe transition, which contribute to the formation of a stabilised daughter 57FeIII component along with the nucleogenic 57FeII forms, are also briefly considered.

Applicability of rep-PCR fingerprinting for identification of Lactobacillus species

PCR amplification of repetitive bacterial DNA elements fingerprinting using the (GTG) 5 primer ((GTG) 5-PCR) was proven to be useful for differentiation of a wide range of lactobacilli (i.e. 26 different (sub)species) at the species, subspecies and potentially up to the strain level. Using this rapid and reproducible genotypic technique, new Lactobacillus isolates recovered from different types of fermented dry sausage could be reliable identified at the (sub)species level. In conclusion, (GTG) 5-PCR was found to be a promising genotypic tool for rapid and reliable speciation and typing of lactobacilli and other lactic acid bacteria important in food-fermentation industries.

Applicability of rep-PCR fingerprinting for identification ofLactobacillusspecies

PCR amplification of repetitive bacterial DNA elements fingerprinting using the (GTG)(5) primer ((GTG)(5)-PCR) was proven to be useful for differentiation of a wide range of lactobacilli (i.e. 26 different (sub)species) at the species, subspecies and potentially up to the strain level. Using this rapid and reproducible genotypic technique, new Lactobacillus isolates recovered from different types of fermented dry sausage could be reliable identified at the (sub)species level. In conclusion, (GTG)(5)-PCR was found to be a promising genotypic tool for rapid and reliable speciation and typing of lactobacilli and other lactic acid bacteria important in food-fermentation industries.

Fragmentation pathways of organoarsenical compounds by electrospray ion trap multiple mass spectrometry (MS 6)

With its detection limit well below 30 pg μl −1 LC–MS–MS has become a sensitive and thus popular analytical technique for organoarsenical compounds. Collision induced dissociation (CID) is a valuable tool for speciation and facilitates a positive identification of the species detected. However, it is not straightforward to understand the fragmentation pathways of organoarsenical compounds when only CID-MS–MS data is available. In the present paper we have investigated multiple mass spectrometry (MS n , n=1, 2, 3, 4, 5, 6) with electrospray CID fragmentation for a number of organoarsenical compounds likely to occur in the environment. The investigated compounds were tetramethylarsonium, trimethylarsinoxide, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, and dimethylarsinoylethanol. By CID of (protonated) organoarsenical cations mostly even-electron fragments are produced after neutral loss processes such as elimination of H 2, H 2O, CH 4, C 2H 2, C 2H 4, C 2H 6, HCHO, CH 3OH, C 2H 5OH, C 2H 4O, and CH 2CO. However, abundant odd-electron fragments are also formed after elimination of radical species. Evidence for reduction of As(V) to As(III) as a driving force in the odd-electron ion formation is obtained.

Metal Kβ X-ray emission spectra of first row transition metal compounds

Abstract A large body of first row transition Kβ X-ray emission spectra are presented and the splitting of the Kβ peak into Kβ′ and Kβ1,3 is quantified by a consistent curvefitting procedure. Broad trends in the Kβ′:Kβ1,3 intensity ratio are identified and related to the oxidation state of the metal and its chemical environment. Implications for the development of X-ray emission spectroscopy as a tool for chemical speciation are considered.

An integrated approach of analytical chemistry

The tremendous development of physical methods of analysis offers an impressive number of tools to simultaneously determine a large number of elements and compounds at very low concentration levels. Todays Analytical Chemistry provides appropriate media to solve technical problems and to obtain correct information about chemical systems in order to take the most appropriate decisions for problem solving. In recent years the development of new strategies for sampling, sample treatment and data exploitation through the research on field sampling, microwaveassisted procedures and chemometrics, additionally the revolution of the analytical methodology provided by the development of flow analysis concepts and process analysis strategies offer a link between modern instrumentation and social or technological problems. The integrated approach of Analytical Chemistry requires correctly incorporating the developments in all of the fields of both, basic chemistry, instrumentation and information theory, in a scheme which considers all aspects of data obtention and interpretation taking also into consideration the side effects of chemical measurements. In this paper, new ideas and tools for trace analysis, speciation, surface analysis, data acquisition and data treatment, automation and decontamination, are presented in the frame of Analytical Chemistry as a problem solving strategy focused on the chemical composition of systems and on the specific figures of merit of the analytical measurements, like accuracy, precision, sensitivity, selectivity but also speed and cost. Technological and industrial, but also environmental, health and social problems, have been considered as challenges for which solution the chemist should select the most appropriate tool and to develop an appropriate strategy.

Biochemical speciation analysis by hyphenated techniques

The elucidation of mechanisms that govern the essentiality and toxicity of trace elements in living organisms is critically dependent upon the possibility of the identification, characterization and determination of chemical forms of these elements involved in life processes. The recent progress and the state-of-the-art of biochemical species-selective trace element analysis are critically evaluated with particular emphasis on the use of techniques combining the high selectivity of high performance liquid chromatography (HPLC) with the elemental or molecular specificity of mass spectrometry [using inductively coupled plasma (ICP) or electrospray ionization (ESI)]. The potential and limitations of hyphenated techniques as a tool for speciation of metals and metalloids in biological materials is discussed using a number of examples drawn from the latest research in the authors’ laboratory.

Radiochemical analysis and speciation of radiocesium in soils by leaching

The specific radiocesium interception potential (SRIP) according to Cremers and Wauters, the repeated leaching technique (RLT) by Kokotov and Popova, and also ammonium competition technique (ACT) are compared as the tools for cesium speciation in solid matrix and assay of soil vulnerability towards radioactive contamination. Reduction of the silver thiourea complex used in the SRIP technique by humic acid is the main hindrance at application of its protocol to real soil samples and humificated alumosilicates. Therefor, the determination of immobile fraction of cesium in soil according to RLT appears to be more advantageous. Uncertainty of its results puts a need for optimization of its performance but common fitting of residual radioactivity measurements is sufficiently precise.

Application of capillary zone electrophoresis–inductively coupled plasma mass spectrometry and capillary isoelectric focusing–inductively coupled plasma mass spectrometry for selenium speciation

The high resolution potential of capillary electrophoresis (CE) makes CE techniques valuable for separations of selenium species, both, organic and inorganic. Such effective separations of charged species are possible using the CZE mode (Z = zone). Very powerful separations can be achieved by capillary isoelectric focusing, when analysing molecules showing different isoelectric points (p I) values, such as organic Se species. Inductively coupled plasma (ICP) MS is an element-specific multi-element detector, providing extremely low detection limits. The combination of CE with ICP-MS promises a powerful tool for metal speciation. Therefore, an online hyphenation of CE [using capillary zone electrophoresis (CZE) or capillary isoelectric focusing (cITP) mode] with ICP-MS, which was developed earlier, was modified and applied to selenium speciation. Separation was differentiated from the detection step during hyphenation. This resulted in short separation times (10 min) and a subsequent detection step lasting 100 s. Firstly, a CZE method was applied, providing a separation of six Se species of interest in one run [Se(IV), Se(VI), selenium carrying glutathione (GSSeSG), selenomethionine (SeM), selenocystine (SeC), selenocystamine (SeCM)]. This CZE method used an alkaline background electrolyte (Na 2CO 3/NaOH). The Se species were separated sufficiently from each other. Detection limits were calculated as 10 or 20 μg Se l −1 for inorganic Se species and 30–50 μg Se l −1 for organic Se species. The method was applied to standard mixtures and body fluids like human milk and serum. Secondly, a cIEF separation (pH range 2–10) was employed for organic Se species only in parallel. Detection limits were around 10–30 μg Se l −1. The method was applied to standard mixtures and body fluids like human milk and serum.

Selenium speciation by interfacing capillary electrophoresis with inductively coupled plasma-mass spectrometry.

The high resolution potential of capillary electrophoresis (CE) makes CE techniques valuable for separations of selenium species. Further, inductively coupled plasma-mass spectrometry (ICP-MS) affords element-specific multi-element detection, providing extremely low detection limits. The combination of CE with ICP-MS promises to become a powerful tool for metal speciation. Therefore, an on-line hyphenation of CE with ICP-MS, which was developed earlier (Michalke, B., Schramel, P., Fresenius' J. Anal. Chem. 1997, 257, 594-599), was modified and applied to selenium speciation. For this reason, capillary zone electrophoresis (CZE) methods were developed, providing the possibility to analyze six Se species of interest in one run: Se (IV), Se (VI), selenium carrying glutathione (GSSeSG), selenomethionine (SeM), selenocystine (SeC), and selenocystamine (SeCM). The final CE method used an alkaline background electrolyte (Na2CO3/NaOH) with separation differentiated from the detection step during hyphenation. This resulted in short separation times (10 min) and a subsequent detection step of 100s. The Se species were sufficiently separated from each other and appeared at 7s (SeCM), 16s (Se [VI]), 22s [SeC], 27s (Se [IV]), 35s [SeM] and 56s (GSSeSG) during the detection step. Detection limits were calculated as 10 or 20 microg Se/L for inorganic Se species and 35-50 microg Se/L for organic Se species.

Hollow fiber based supported liquid membrane: a novel analytical system for trace metal analysis

A new versatile tool for speciation of trace metals, in particular Cu, Pb and Cd based on a hollow fiber supported liquid membrane (HFSLM) consisting of 1,10-didecyl diaza 18-crown-6, fatty acid and a mixture of toluene and phenylhexane (1 + 1) has been studied for application in natural water conditions. Two types of single hollow fiber modules i.e. non flow and flow systems for free metal ion separation and preconcentration were used. The effect of target elements, sample volume, target metal concentration, and flow rates of sample solution in the case of the flow system on the preconcentration factor for a given receiver solution volume (ca 50–60 μl) placed in the lumen of the membrane) have been studied. High preconcentration factors in the range 100–3000 for Cu, Pb and Cd, for preconcentration times in the range 5–120 min were found using sample and receiver solution volumes of 250 ml and 60 μl, respectively. Preconcentration factors were found to be independent of the initial concentration of target elements in the sample and dependent on initial sample volume. Long term stabilities of these membranes showed that they are stable for at least seven days of continuous use. The results of these studies suggest that by combining SLM with sensitive analytical detectors e.g., voltammetric ones, detection limits of below 10 −10 mol l −1 can be achieved.