Trends in speciation analysis of vanadium in environmental samples and biological fluids--a review

A comprehensive review is presented addressing recent trends in the speciation and determination of vanadium in environmental and biological sample matrices, including important analytical aspects such as sample clean up, pre-concentration and method development. Methodology based on both separation and spectroscopic techniques for the determination of vanadium speciation is discussed. A brief outline of analytical principles, together with an overview of the recent developments and applications of vanadium speciation determination is included. The newer methods for detecting metal ions including hyphenated spectroscopic techniques and sample preparation schemes are also discussed.     

Speciation analysis — why and how?

Summary The different aspects of speciation analysis are reviewed. Species-specific instrumental techniques as well as various speciation schemes are considered for the determination of species of metals and metalloids, including organometallic compounds. The application of the methods are discussed in some detail for the analysis of natural waters, air, soil, sediment and biological samples. The relationship between metal species and bioavailability is also briefly dealt with.     

Analysis of selenium species by capillary electrophoresis

The presence of selenium in the form of different species in environmental and biological samples receives an increasing attention due to better understanding of its bioavailability, toxicity and transport mechanism. For many years, gas and liquid chromatography have been extensively explored in speciation analysis of this element. Recently, capillary electrophoresis (CE) has made much progress in this field. This review presents the developments in the application of CE for simultaneous separation and determination of different selenium compounds. Various separation approaches and detection methods as well as pre-concentration techniques are discussed. The speciation performance of CE is illustrated by a number of practically relevant applications.     

Speciation analysis of heavy metals in natural waters: a review.

Metal speciation in natural waters is of increasing interest and importance because toxicity, bioavailability, environmental mobility, biogeochemical behavior, and potential risk in general are strongly dependent on the chemical species of metals. This paper provides an overview of the need for speciation of heavy metals in natural waters, the chemical and toxicological aspects of speciation, and the analytical procedures for separation and the different techniques for final determination that are used today. The trends and developments of speciation are also discussed. Finally, the case of chromium (Cr) was selected for a detailed presentation because the speciation of this metal has attracted a great deal of interest in view of the toxic properties of Cr(VI).     

Analytical methods for determination of free metal ion concentration, labile species fraction and metal complexation capacity of environmental waters: A review

Different experimental approaches have been suggested in the last few decades to determine metal species in complex matrices of unknown composition as environmental waters. The methods are mainly focused on the determination of single species or groups of species.The more recent developments in trace elements speciation are reviewed focusing on methods for labile and free metal determination.Electrochemical procedures with low detection limit as anodic stripping voltammetry (ASV) and the competing ligand exchange with adsorption cathodic stripping voltammetry (CLE-AdCSV) have been widely employed in metal distribution studies in natural waters. Other electrochemical methods such as stripping chronopotentiometry and AGNES seem to be promising to evaluate the free metal concentration at the low levels of environmental samples. Separation techniques based on ion exchange (IE) and complexing resins (CR), and micro separation methods as the Donnan membrane technique (DMT), diffusive gradients in thin-film gels (DGT) and the permeation liquid membrane (PLM), are among the non-electrochemical methods largely used in this field and reviewed in the text. Under appropriate conditions such techniques make possible the evaluation of free metal ion concentration.     

Determination of 241Am in Environmental Samples: A Review

The determination of ²⁴¹Am in the environment is of importance in monitoring its release and assessing its environmental impact and radiological risk. This paper aims to give an overview about the recent developments and the state-of-art analytical methods for ²⁴¹Am determination in environmental samples. Thorough discussions are given in this paper covering a wide range of aspects, including sample pre-treatment and pre-concentration methods, chemical separation techniques, source preparation, radiometric and mass spectrometric measurement techniques, speciation analyses, and tracer applications. The paper focuses on some hyphenated separation methods based on different chromatographic resins, which have been developed to achieve high analytical efficiency and sample throughput for the determination of ²⁴¹Am. The performances of different radiometric and mass spectrometric measurement techniques for ²⁴¹Am are evaluated and compared. Tracer applications of ²⁴¹Am in the environment, including speciation analyses of ²⁴¹Am, and applications in nuclear forensics are also discussed.     

Determination of rare earth elements in natural water samples – A review of sample separation,preconcentration and direct methodologies

This review discusses and compares the methods given for the determination of rare earth elements (REE) in natural water samples, including sea, river, lake, tap, ground and waste waters as well as Antarctic ice. Since REE are at very low concentrations in natural waters, numerous different preconcentration methods have been proposed to enable their measurement. These include liquid liquid extraction, dispersive liquid-liquid micro-extraction and solidified floating drop micro-extraction. In addition to liquid-liquid extraction methods, solid phase extraction using commercial resins, resins made in-house, silica-based exchange materials and other solid media is also discussed. These and other techniques such as precipitation/co-precipitation and flotation are compared in terms of speed, preconcentration factors achieved, precision, accuracy and limits of detection (LOD). Some papers have discussed the direct determination of REE in these sample types. Some have used specialised sample introduction systems such as ultrasonic nebulization whereas others have used a standard sample introduction system coupled with inductively coupled plasma mass spectrometry (ICP-MS) detection. These direct methods have also been discussed and compared.     

A methodological study of mercury speciation using dogfish liver CRM (DOLT-2)

The purpose of the study was to optimise analytical methods for determination of the chemical speciation of mercury in studies of protective mechanisms of selenium. Optimisation of the methods was performed using CRM DOLT-2 (Dogfish liver), both in its original form and after separation of various fractions. The sample was homogenised with 10 mM Tris-HCl buffer (pH 7.6) and ultracentrifuged. The soluble phase obtained was applied to a size exclusion chromatography column (Sephadex G-75 column) for separation of various protein fractions. Total mercury (total Hg), monomethyl mercury (MeHg) and selenium (Se) were determined in whole dogfish liver tissue and its soluble and insoluble phases (pellet). Different approaches for determination of total Hg and MeHg were compared. Simultaneous determination of MeHg and inorganic mercury (Hg2+) was based on alkaline dissolution and/or acid leaching, followed by ethylation, room temperature precollection, isothermal gas chromatography (GC), pyrolysis and detection with cold vapour atomic fluorescence spectrometry (CVAFS). The sum of MeHg and Hg2+ was compared to total Hg results obtained by acid digestion and CVAAS detection. The accuracy of MeHg determination was checked by its determination using acid leaching at room temperature, solvent extraction, back extraction into Milli-Q water, ethylation, GC and CVAFS detection. For the insoluble phase it is recommended to use solvent extraction for MeHg and acid digestion CVAAS for total Hg. For determination of MeHg and Hg2+ in the lyophilised sample and water soluble fractions containing low concentrations of mercury species, the simultaneous measurement of MeHg and Hg2+ after alkaline dissolution is the most appropriate method.     

The speciation of trace elements in waters

Speciation (determination of the different physico-chemical species formed by an element) in a water sample is necessary for an understanding of the toxicity, bioavailability, bioaccumulation and transport of a particular element. The importance of speciation measurements and the various factors leading to changes in speciation are discussed in this review. Speciation in natural waters is a difficult task, and the analytical methods available and the results obtained are critically assessed.     

Organised surfactant assemblies in analytical atomic spectrometry

The use of surfactant-based organised assemblies in analytical atomic spectroscopy is extensively and critically reviewed along three main lines: first, the ability of organised media to enhance detection of atomic spectroscopic methods by favourable manipulation of physical and chemical properties of the sample solution second, the extension of separation mechanisms by resorting to organised media and third a discussion of synergistic combinations of liquid chromatography separations and atomic detectors via the use of vesicular mobile phases. Changes in physical properties of sample solutions aspirated in atomic spectrometry by addition of surfactants can be advantageously used in at least four different ways: (i) to improve nebulisation efficiency; (ii) to enhance wettability of solid surfaces used for atomisation; (iii) to improve compatibility between aqueous and organic phases; and (iv) to achieve good dispersion of small particles in “slurry” techniques. Controversial results and statements published so far are critically discussed.The ability of surfactant-based organised assemblies, such as micelles and vesicles, to organise reactants at the molecular level has also been applied to enhance the characteristics of chemical generation of volalite species of metals and semi-metals (e.g., hydride or ethylide generation of As, Pb, Cd, Se, Sn, and cold vapour Hg generation) used in atomic methods. Enhancements in efficiency/transport of volatile species, increases in the reaction kinetics, stabilisation of some unstable species and changes in the selectivity of the reactions by surfactants are dealt with.Non-chromatographic cloud-point separations to design pre-concentration procedures with subsequent metal determination by atomic methods are addressed along with chromatographic separations of expanded scope by addition of surfactants to the conventional aqueous mobile phases of reversed-phase high-performance liquid chromatography.Finally, the synergistic effect of using vesicles to improve both the separation capabilities of reversed-phase HPLC and the detectability of atomic detectors by on-line vesicular hydride generation is described. In particular, the possible separation mechanisms responsible for micellar and vesicular mobile phases in reversed-phase chromatographies are analysed and compared. The possible effect of modification of stationary phases by monomers of the surfactants should also be taken into account. The application of such on-line couplings to develop new hybrid approaches to tackle modern problems of trace element speciation for As, Hg, Se, and Cd completes this revision of the present interface between analytical atomic spectroscopy and surfactant-based organised assemblies.     

A methodological study of mercury speciation using Dogfish liver CRM (DOLT-2)

The purpose of the study was to optimise analytical methods for determination of the chemical speciation of mercury in studies of protective mechanisms of selenium. Optimisation of the methods was performed using CRM DOLT-2 (Dogfish liver), both in its original form and after separation of various fractions. The sample was homogenised with 10 mM Tris-HCl buffer (pH 7.6) and ultracentrifuged. The soluble phase obtained was applied to a size exclusion chromatography column (Sephadex ¶G-75 column) for separation of various protein fractions. Total mercury (total Hg), monomethyl mercury (MeHg) and selenium (Se) were determined in whole dogfish liver tissue and its soluble and insoluble phases (pellet). Different approaches for determination of total Hg and MeHg were compared. Simultaneous determination of MeHg and inorganic mercury (Hg²⁺) was based on alkaline dissolution and/or acid leaching, followed by ethylation, room temperature precollection, isothermal gas chromatography (GC), pyrolysis and detection with cold vapour atomic fluorescence spectrometry (CVAFS). The sum of MeHg and Hg²⁺ was compared to total Hg results obtained by acid digestion and CVAAS detection. The accuracy of MeHg determination was checked by its determination using acid leaching at room temperature, solvent extraction, back extraction into Milli-Q water, ethylation, GC and CVAFS detection. For the insoluble phase it is recommended to use solvent extraction for MeHg and acid digestion CVAAS for total Hg. For determination of MeHg and Hg²⁺ in the lyophilised sample and water soluble fractions containing low concentrations of mercury species, the simultaneous measurement of MeHg and Hg²⁺ after alkaline dissolution is the most appropriate method.     

Analysis of trace elements and their physico-chemical forms in natural waters

Trace elements in natural waters can be present in different physico-chemical forms, varying in size, charge and density properties. Knowledge of speciation is essential for understanding the transport, distribution, and biological uptake of trace elements in the environment. The development of techniques to provide reliable information on physico-chemical forms has, therefore, become a challenge within Analytical Chemistry.When selecting analytical methods for the determination of total concentrations or fractions of trace elements in natural waters, no exclusion of species should occur, or at least it must be accounted for. Furthermore, the determination limits must be sufficiently low to allow the actual concentrations to be determined with reasonable precision and accuracy. For very low concentrations, preconcentration techniques are applicable, provided the chemical yield of the spike represents that of the original species present. For methods meeting these criteria, the suitability for routine analysis should be considered.When the physico-chemical forms of trace elements are to be determined, the fractionation should take placein situ or shortly after sampling. As the concentrations involved in speciation studies may be extremely low, there is an increasing awareness of potential sources of errors influencing analytical results. Sample collection and separation/fractionation/concentration procedures prior to analysis are, therefore, essential within Analytical Chemistry, and the whole procedure must be taken into account when interpreting the results. There are, however, several requirements which should be met by techniques applicable for speciation purposes. In general, size fractionation techniques (e.g.in situ hollow fibre ultrafiltration) should be applied prior to the addition of any chemical reagents (charge fractionation techniques).     

UV irradiation controlled cold vapor generation using SnCl2 as reductant for mercury speciation.

A simple and ultrasensitive method, which was based on cold vapor generation (CVG) coupled to atomic fluorescence spectrometry (AFS), was proposed for speciation analysis of inorganic mercury (Hg2+) and methylmercury (MeHg) in water samples. In the presence of UV irradiation, all the mercury (MeHg+Hg2+) in a sample solution can be reduced to Hg0 by SnCl2; without UV irradiation, only Hg2+ species can be determined. So the concentration of MeHg can be obtained from the difference of the total mercury and Hg2+ concentration; thus, speciation analysis of Hg2+ and MeHg was simply achieved without chromatographic separation. Under the optimized experimental conditions, the limits of detection were 0.01 ng mL-1 for both Hg2+ and MeHg. The sensitivity and limit of detection were not dependent on the mercury species, and a simple Hg2+ aqueous standard series can be used for the determination of both Hg2+ and MeHg.     

Speciation analysis for mercury in gas condensates by capillary gas chromatography with inductively coupled plasma mass spectrometric detection

A method allowing species-selective determination of atomic mercury, non-polar dialkylated mercury compounds,polar monoalkylated species and inorganic mercury complexes in natural gas condensates was developed. Inductively coupled plasma mass spectrometry was employed as a detection method for capillary gas chromatography and compared with microwave induced plasma atomic emission detection for the analysis of hydrocarbon-rich matrices. The method was based on two consecutive injections allowing comprehensive speciation analysis. First a sample aliquot was diluted with toluene and analysed for Hg0 and individual dialkylmercury compounds. Then, another aliquot was butylated with a Grignard reagent for the species specific determination of Hg(II) and monoalkylated mercury species. The detection limits were down to 0.08 pg level.     

Mercury speciation by CE: a review

CE methods for the speciation of inorganic and organomercury compounds are reviewed. Sample preparation, separation conditions and detection modes are discussed. Efficient separation and sensitive determination of mercury species by CE typically involves complexation with various thiols, chromogenic and other chelating agents; however, some methods do not require complexation. Spectrophotometric detection based on UV-visible absorption is by far the most commonly used. Hyphenated techniques, such as CE/inductively coupled plasma (ICP)-MS, hydride generation coupled to ICP-MS or atomic fluorescence spectrometry and CE/atomic absorption spectrometry are gaining popularity due to their high sensitivity and selectivity. Last, but not least, the potential and applications of electrochemical methods for detection of separated mercury species are outlined.     

Determination of Hg in seawater by inductively coupled plasma mass spectrometry after on-line pre-concentration

A method for the determination of Hg in seawater by inductively coupled plasma mass spectrometry, after an on-line separation and pre-concentration, is described. The matrix separation was accomplished by retention of the Hg complex with the ammonium salt of O,O-diethyl dithiophosphoric acid on C₁₈ immobilized on silica in a micro-column. Before pre-concentration, the seawater sample was acidified with HNO₃ to 0.14 mol l⁻¹. Methanol was used as the eluent, which was introduced into the conventional pneumatic nebulizer of the instrument. External calibration with aqueous analytical solutions, submitted to the same procedure, was used. An enhancement factor of 16 was obtained, and the limit of detection was 5 ng l⁻¹. The sample consumption was 2.3 ml per determination, and the sampling frequency was 21 h⁻¹. The accuracy was tested by comparison with vapor generation inductively coupled plasma mass spectrometry. The agreement between the Hg concentrations measured by the two methods in the seawater samples was good.     

Electrospray mass spectrometry: a tool for elemental speciation

Recent progress in the development of electrospray mass spectrometry (ESMS) as a tool for elemental speciation is reviewed. Reports wherein ESMS is used to qualitatively determine the presence of metal ions (inorganic, organometallic and complexed) and non-metallic inorganic species have grown exponentially over the last decade. In addition to elemental speciation, impact in other areas such as gas-phase chemistry, inorganic–organometallic chemistry and biological mass spectrometry has been prolific. The review is structured to cover each of the areas listed above, and also includes a brief introduction, discussion of the electrospray process, discussion of instrumentation and other relevant application areas. An overview of the types of species/complexes studied is given in each section along with a brief discussion of the application objectives and analytical aspects. Analytical considerations for the development of ESMS as a tool for elemental speciation are also raised, including, application, quantitation, sensitivity, limitations and future directions. The impact of speciation strategies involving stand-alone ESMS, ESMS coupled with on-line separation techniques and the inclusion of ESMS in dual (multiple) technique strategies are presented. High backgrounds due to chemical noise and signal suppression (matrix effects) appear to be two important factors limiting sensitive detection of most analytes. The use of sample pre-treatment, pre-concentration or separation techniques is necessary to alleviate these problems. Although ESMS currently suffers from a number of limitations, continued instrumentation and methods development will improve its capability and diversify the impact of ESMS as a tool for elemental speciation.     

Non-chromatographic hydride generation atomic spectrometric techniques for the speciation analysis of arsenic,antimony, selenium,and tellurium in water samples—a review

Hydride generation (HG) coupled with AAS, ICP–AES, and AFS techniques for the speciation analysis of As, Sb, Se, and Te in environmental water samples is reviewed. Careful control of experimental conditions, offline/online sample pretreatment methods employing batch, continuous and flow-injection techniques, and cryogenic trapping of hydrides enable the determination of various species of hydride-forming elements without the use of chromatographic separation. Other non-chromatographic approaches include solvent extraction, ion exchange, and selective retention by microorganisms. Sample pretreatment, pH dependency of HG, and control of NaBH₄/HCl concentration facilitate the determination of As(III), As(V), monomethylarsonate (MMA), and dimethylarsinate (DMA) species. Inorganic species of arsenic are dominant in terrestrial waters, whereas inorganic and methylated species are reported in seawater. Selenium and tellurium speciation analysis is based on the hydrides generation only from the tetravalent state. Se(IV) and Se(VI) are the inorganic selenium species mostly reported in environmental samples, whereas speciation of tellurium is rarely reported. Antimony speciation analysis is based on the slow kinetics of hydride formation from the pentavalent state and is mainly reported in seawater samples.     

Determination of plutonium in environmental samples with quadrupole ICP-MS

A method for rapid determination of plutonium isotopes in environmental samples with ultrasonic nebulisation and quadrupole ICP-MS detection was established. Techniques for sample dissolution, pre-concentration and chemical separation were evaluated and the optimal scheme outlined. Comparisons with α-spectrometry and high resolution ICP-MS confirmed the suitability of the method when applied to different environmental matrices within the global fallout concentration range in the northern hemisphere as well as more contaminated sites. Operational detection limits were 0.5–1.5 fg/l for fresh waters and 0.03–0.1 ng/kg for lake sediments and saline marsh sediments.     

Preconcentration of Trace Elements in Water for Speciation Studies

Trace element speciation has recently become one of the most important problems in water analysis. Proper combination of preconcentration techniques with instrumental determination methods is essential to speciation analysis, because sensitivity and selectivity of direct determination methods are generally lacking. The present paper describes such preconcentration techniques as filtration, centrifugation, flotation and sorption, which have been developed in the author's laboratory for the speciation of heavy metals in river and pond waters by electron microscopy, X-ray microanalysis and chemical analysis. The application of freeze concentration to the speciation of silica in high-purity waters is also discussed.