Elemental Speciation Analysis Research Articles

What can the different current-detection methods offer for element speciation?

Elemental mass spectrometry (MS) has revolutionized the field of element speciation in the past decade. Since the late 1990s, molecular MS has increasingly become more popular. Although the potential of the latter technique has been recognized by the element-speciation community, it has not yet gained general acceptance. Only recently, the tool-box of the analyst interested in element speciation has expanded dramatically due to the technical developments in molecular MS and in X-ray absorption spectroscopy (XAS). In particular, the development of more user-friendly ionization methods, such as atmospheric pressure chemical ionization (APCI), electrospray (ES), matrix-assisted laser desorption/ionization (MALDI) and, most recently, atmospheric pressure photoionization (APPI), as well as the installation of ultra-dilute XAS stations, has made it possible for these methods to be applied for element-speciation analysis of heterogeneous real samples. These and other emerging techniques will be discussed, especially in the light of the new challenges in element speciation, i.e. the detection of unstable short-lived species and macromolecules. This review attempts to show the advantages and the limitations of the various techniques, their combinations in off-line set-ups and on-line dual-detection modes for the analysis of mainly biological and environmental samples.

Capillary electrophoresis of inorganic ions: An update

This review as a sequel of three earlier similar reports gives a summary of the progress and significant methodological developments, starting from 2002, in the use of capillary electrophoresis (CE) for inorganic ion analysis. As substantiated by the illustrative number of relevant references, improvements in sensitivity achieved both in and outside a CE system, advances in manipulating the separation selectivity, novel hardware configurations, and system performance innovations are continually being reported over the review period. Specifically viewed are the recent advancements in elemental (bio)speciation analysis, which remains one of the most fertile areas of CE research, as well as in three recently booming research topics: contactless conductivity detection, separations on microchips, and transient isotachophoretic preconcentration. A state-of-the-art picture of technique's potentialities within the field of interest presented here demonstrates that CE has become recognized and is growing in acceptance as a reliable alternative to traditional analytical methods such as high-performance liquid chromatography (HPLC).

Plasma-source mass spectrometry for speciation analysis: state-of-the-art

Current and emerging capabilities of plasma-source mass spectrometry (PS-MS) as it is employed for elemental speciation analysis are reviewed. Fundamental concepts and their advantageous aspects, experimental conditions, and analytical performance are described and illustrated by recent examples from the literature. Novel instrumentation, techniques, and strategies for inductively-coupled plasma mass spectrometry (ICP-MS), microwave-induced plasma (MIP) mass spectrometry, glow-discharge (GD) mass spectrometry, and electrospray ionization (ESI), among others, are described. The use of ionization sources that provide tunable ionization, others that can be modulated between different sets of operating conditions, and others used in parallel is also examined.

Determination of trace elements bound to soil and sediment fractions (IUPAC Technical Report)

Abstract This paper presents an overview of methods for chemical speciation analysis of elements in samples of sediments and soils. The sequential leaching procedure is thoroughly discussed, and examples of different applications are shown. Despite some drawbacks, the sequential extraction method can provide a valuable tool to distinguish among trace element fractions of different solubility related to mineralogical phases. The understanding of the speciation of trace elements in solid samples is still rather unsatisfactory because the appropriate techniques are only operationally defined. The essential importance of proper sampling protocols is highlighted, since the sampling error cannot be estimated and corrected by standards. The Community Bureau of Reference (BCR) protocols for sediment and soil give a good basis for most of the solid samples, and the results can be compared among different laboratories.

Isotope-dilution ICP-MS for trace element determination and speciation: from a reference method to a routine method?

This critical review discusses the conditions under which inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS) is suitable as a routine method for trace element and element-speciation analysis. It can, in general, be concluded that ICP-IDMS has high potential for routine analysis of trace elements if the accuracy of results is of predominant analytical importance. Hyphenated techniques with ICP-IDMS suffer both from lack of commercially available isotope-labeled spike compounds for species-specific isotope dilution and from the more complicated system set-up required for species-unspecific ICP-IDMS analysis. Coupling of gas or liquid chromatography with species-specific ICP-IDMS, however, enables validation of analytical methods involving species transformations which cannot easily be performed by other methods. The potential and limitations of ICP-IDMS are demonstrated by recently published results and by some unpublished investigations by our group. It has been shown that possible loss of silicon as volatile SiF4 during decomposition of a sample by use of hydrofluoric acid has no effect on trace silicon determination if the isotope-dilution step occurs during digestion in a closed system. For powder samples, laser ablation ICP-IDMS can be applied with an accuracy comparable with that only available from matrix-matched standardization, whereas the accuracy of electrothermal vaporization ICP-IDMS was strongly dependent on the element determined. The significance of easy synthesis of isotope-labeled spike compounds for species-specific ICP-IDMS is demonstrated for monomethylmercury and Cr(VI). Isotope-exchange reactions between different element species can prevent the successful application of ICP-IDMS, as is shown for iodinated hydrocarbons. It is also shown for monomethylmercury that species transformations during sample-pretreatment steps can be followed by species-specific ICP-IDMS without loss of accuracy. A relatively simple and time-efficient procedure for determination of monomethylmercury in environmental and biological samples is discussed. The method, which entails a rapid microwave-assisted isotope dilution step and in-situ extraction of the derivatized species, has good potential for routine application in the future.

Elemental speciation analysis in capillary electrophoresis.

The growing awareness of the strong development of the toxicity of heavy metals upon their chemical forms has led to an increasing interest in the qualitative and quantitative determination of specific metal species. Speciation has therefore become an important topic of present-day analytical research. The development in the elemental speciation analysis by capillary electrophoresis (CE) is reviewed. Various CE separation modes and detection techniques applied are discussed. A comprehensive description of reported methods to date in CE speciation analysis including metals, metalloids and nonmetallic elements is demonstrated. Some examples are presented to demonstrate CE's ability to solve real-world speciation analysis with emphasis on the applications in biological and environmental samples. Further, some issues concerning the limitations and the future of CE with regard to speciation studies are also discussed.

Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils

Rhizosphere is a microbiosphere and has quite different chemical, physical and biological properties from bulk soils. A greenhouse experiment was performed to compare the difference of fractionation and bioavailability of trace elements Cr, Ni, Zn, Cu, Pb and Cd between rhizosphere soil and bulk soil. In the meantime, the influence of air-drying on the fractionation and bioavailability was also investigated by using wet soil sample as a control. Soils in a homemade rhizobox were divided into four zones: rhizosphere, near rhizosphere, near bulk soil and bulk soil zones, which was designated as S 1, S 2, S 3 and S 4. Elemental speciations were fractionated to water soluble, exchangeable and carbonate bound (B1), Fe–Mn oxide bound (B2), and organic and sulfide bound (B3) by a sequential extraction procedure. Speciation differences were observed for elements Cr, Ni, Zn, Cu, Pb and Cd between the rhizosphere and bulk soils, and between the air-dried and wet soils as well. The concentrations of all six heavy metals in fraction B1 followed the order of S 2>S 3>S 1>S 4 and for B2, the order was S 2>S 3≈S 4>S 1. For B3, the order was S 1>S 3≈S 4>S 2, while for Cd the order was S 2>S 3≈S 4>S 1. The air-drying increased elemental concentration in fractions B1 and B2 by 20–50% and decreased in fraction B3 by about 20–100%. Correlation analysis also indicated that the bioavailability correlation coefficient of fraction B1 in rhizosphere wet soil to plants was better than that between either air-dried or nonrhizosphere soils. Therefore, application of rhizosphere wet soils should be recommended in the future study on the speciation analysis of trace elements in soils and bioavailability.

Speciation analysis of trace elements in the brains of individuals with Alzheimer's disease with special emphasis on metallothioneins

A speciation analysis of protein-bound elements in the cytosol of human brain was achieved by size exclusion chromatographical separation of the biomolecules and on-line detection of the metal profiles in the eluate by hyphenated inductively coupled plasma-mass spectrometry. Post-mortem samples from Alzheimer's disease brains and from brains of a control group were investigated to elucidate changes in the trace element distribution during the pathological process. Special attention was paid to the metallothioneins (MT) - cysteine-rich, metal-binding proteins of low molecular weight, existing in several isoforms. The isoform MT-3 is found especially in the brain and has a growth inhibition function on neurons. The MT peaks were identified in the element profiles. For this purpose, the metal binding capability and the heat stability of MT were taken into consideration. For verification, a comparison with pure MT-3 was carried out and further biochemical and analytical methods were applied to the fractions of the chromatographical run. A comparison between Alzheimer's disease and control brains showed a significant difference concerning the MT-1/-2 and MT-3 metal levels, leading to the assumption that there were oxidative processes having taken place in the Alzheimer's brain samples.

Elemental Speciation Analysis by Capillary Electrophoresis with ICP MS and Electrospray Mass Spectrometric Detection

The status of capillary zone electrophoresis (CZE) with elementand molecule specific detection in bio-inorganic speciation analysis is discussed. The current challenges: interfacing CZE to inductively coupled plasma mass spectrometry (ICP MS) to insure the maximum detection sensitivity and separation efficiency, and the parallel use of electrospray MS for peak identification are highlighted using an example of analyzing for cadmium-metallothionein complexes in rat liver. The need for the elimination of the biological matrix by sample fractionation using size-exclusion chromatography prior to CZE is emphasized.

Comparison of speciation and bioavailability of rare earth elements between wet rhizosphere soil and air-dried bulk soil

A comparison was made between the speciation and bioavailability of rare earth elements in rhizosphere and nonrhizosphere soils and between wet and air-dried soils under greenhouse conditions by using a homemade rhizobox. The speciation of rare earth elements in soils is experimentally defined as water soluble, exchangeable and carbonate bound (B1), Fe–Mn oxide bound (B2) and organic matter and sulfide bound (B3). The air-drying process of the wet soils resulted in an increase in rare earth elements in fractions B1 and B2, and a decrease in B3. Generally, a better correlation was obtained between the speciation and bioavailability by using wet soils than that by using air-dried soils, and as the conditions in the former are close to the realistic conditions of plant growth in the environment better plant availability is also achieved between the speciation of rare earth elements in the rhizosphere soils than that in the nonrhizosphere soils. Application of the rhizosphere wet soils is be strongly recommended in the future study on the speciation analysis and bioavailability of trace elements in soils.

Determination of arsenic compounds by high-performance liquid chromatography-ultrasonic nebulizer-high power nitrogen-microwave-induced plasma mass spectrometry: an accepted coupling.

To establish a sensitive, accurate, and precise determination of arsenic compounds, a high power nitrogen microwave-induced plasma (1.3 kW) mass spectrometer (N2-MIP-MS) has been successfully coupled with an ultrasonic nebulizer (HPLC-USN) that is attached to a high-performance liquid chromatograph. It is examined as an element-specific detector for its applicability to the optimization and determination of seven arsenic compounds [arsenic acid, methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenobetaine (AB), arsenocholine (AC), trimethylarsine oxide (TMAO), and tetramethylarsonium ion (CMI)]. This HPLC-USN-MIP-MS coupling is an encouraging combination as an alternative method for mass spectroscopy for elemental speciation analysis. Interchanging of the MIP-MS fabricated nebulizer (concentric) with an ultrasonic nebulizer, increases 3-6 times the ion signals for the anionic and 6-12 times those for the cationic arsenic compounds as compared to traditional methods. The HPLC-USN-MIP-MS combination used is excellent, amplifying the ion signals about 1.5-2 times for cationic and 1.3-2.8 times for the anionic arsenic compounds as compared to the HPLC-ICPMS coupling. The detection limits for As(V), MA, DMA, AB, TMAO, AC, and TMI (in Milli-Q-water) obtained with the optimized HPLC-USN-N2-MIP-MS system are 0.46, 0.36, 0.73, 0.21, 3.64, 0.39, and 0.32 microg L(-1), respectively, about 13-50 times lower than the HPLC-MIP-MS and about 3-11 times lower than the HPLC-ICPMS. The detection limits of As(V), MA, DMA, AB, TMAO, AC, and TMI, which spike in the urine, are deteriorated by 1.7-4.2 times compared with the detection limits of the seven different As compounds, which are prepared in the Milli-Q-water. The repeatability (RSD for three successive analyses) and reproducibility (RSD for three successive analyses performed on three different days), considering peak area and peak height, achieved for seven different arsenic compounds are 0.5-7 and 0.7-8%, comparable with the HPLC-ICPMS (0.3-8.5%; 4-12%) and HPLC-MIP-MS (0.4-9%; 5-12%) systems. The combined HPLC-USN-N2-MIP-MS has been adequately applied to the determination of AB in NIES Candidate Human Urine CRM. The results agree with the HPLC-ICPMS values. Chloride interference as 40Ar35Cl+ is not found in the urine and with the high chloride matrix (10000 mg L(-1)).

Gas and liquid chromatography with inductively coupled plasma mass spectrometry detection for environmental speciation analysis — advances and limitations

Recent advances in the coupling of gas chromatography (GC) and high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP MS) and their role in trace element speciation analysis of environmental materials are presented. The discussion is illustrated with three research examples concerning the following topics: (i) development and coupling of multicapillary microcolumn GC with ICP MS for speciation of organotin in sediment and biological tissue samples; (ii) speciation of arsenic in marine algae by size-exclusion-anion-exchange HPLC-ICP MS; and (iii) speciation of cadmium in plant cell cultures by size-exclusion HPLC-ICP MS. Particular attention is paid to the problem of signal identification in ICP MS chromatograms; the potential of electrospray MS/MS for this purpose is highlighted.

Elemental speciation analysis in biochemistry by electrospray mass spectrometry

The recent advances and trends in the development and applications of electrospray mass spectrometry (ESI-MS) to speciation analysis are highlighted. The use of the different operational modes of ESI-MS: elemental mode (source collision-induced dissociation (SCID)), molecular mode (MS of protonated molecule ions) and tandem MS mode (product ion scan of the collision-induced dissociation (CID) products of the protonated molecule ion), is discussed. Advantages and limitations of ESI-MS for signal identification in high performance liquid chromatography (HPLC)–ICP-MS and as a free-standing tool for species-selective analysis are highlighted. The discussion is illustrated with a number of examples related to the trace element speciation in biochemistry, viz. selenium in yeast, arsenic in seaweeds, cobalamins in pharmaceutical preparations, and Cd complexes with phytochelatins and metallothioneins in plant and animal tissues

Trace element speciation analysis of biomaterials by high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

The recent advances in the coupling of HPLC with ICP-MS and its role in trace element speciation analysis of biological materials are discussed. Methodological approaches involving different chromatographic separation mechanisms (size exclusion, ion exchange and reversed phase) are presented for speciation of organometalloid species (arsenic and selenium) and of metal complexes with polypeptide and polysaccharide ligands. Problems related to species-selective analysis in water-insoluble fractions of solid samples and to signal identification in HPLC–ICP-MS chromatograms are highlighted. The discussion is illustrated with data recently obtained in metal speciation studies in plant and animal biochemistry.

Unique possibilities offered by radio-tracers for speciation analysis of trace elements in biological fluids and tissues.

Speciation analysis of trace elements is the identification and/or measurement of the quantities of one or more individual chemical species in a sample. The general procedure starts with the separation of the species followed by the measurement of trace elements in the different fractions. The identification of the species may be done by UV-detection, mass spectrometry or other techniques. For the development of the methodology, and for in-vivo and in-vitro studies radiotracers are ideally suited. In speciation analysis of trace elements in biological fluids and tissues the search goes on for small inorganic and organometallic compounds, and for metal-protein complexes.

Sample Preparation and Storage Can Change Arsenic Speciation in Human Urine

Stability of chemical speciation during sample handling and storage is a prerequisite to obtaining reliable results of trace element speciation analysis. There is no comprehensive information on the stability of common arsenic species, such as inorganic arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine, in human urine. We compared the effects of the following storage conditions on the stability of these arsenic species: temperature (25, 4, and -20 degrees C), storage time (1, 2, 4, and 8 months), and the use of additives (HCl, sodium azide, benzoic acid, benzyltrimethylammonium chloride, and cetylpyridinium chloride). HPLC with both inductively coupled plasma mass spectrometry and hydride generation atomic fluorescence detection techniques were used for the speciation of arsenic. We found that all five of the arsenic species were stable for up to 2 months when urine samples were stored at 4 and -20 degrees C without any additives. For longer period of storage (4 and 8 months), the stability of arsenic species was dependent on urine matrices. Whereas the arsenic speciation in some urine samples was stable for the entire 8 months at both 4 and -20 degrees C, other urine samples stored under identical conditions showed substantial changes in the concentration of As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid. The use of additives did not improve the stability of arsenic speciation in urine. The addition of 0.1 mol/L HCl (final concentration) to urine samples produced relative changes in inorganic As(III) and As(V) concentrations. Low temperature (4 and -20 degrees C) conditions are suitable for the storage of urine samples for up to 2 months. Untreated samples maintain their concentration of arsenic species, and additives have no particular benefit. Strong acidification is not appropriate for speciation analysis.

Application of a nitrogen microwave-induced plasma mass spectrometer as an element-specific detector for arsenic speciation analysis

A high power nitrogen microwave-induced plasma (1.3 kW) mass spectrometer (N2-MIP-MS) was successfully coupled with an HPLC system using a silica-based cation-exchange column. It was examined as an element-specific detector for its applicability to the optimization and determination of seven arsenic compounds [As(V), methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenobetaine (AB), arsenocholine (AC), trimethylarsine oxide (TMAO) and tetramethylarsonium ion (TMI)]. The system is a promising alternative ion source for mass spectrometry for elemental speciation analysis. The MIP was stable with a pyridine mobile phase for up to 6 h. Replacing the MIP-MS fabricated nebulizer (concentric) and sample input tubing (PTFE) with an ICP-MS (PMS-2000) nebulizer (concentric) and PEEK tubing increased the ion signals for anionic and cationic arsenic compounds by 17–30 and 21–25%, respectively. PEEK tubing additionally increased the separation efficiency for the arsenic compounds. The detection limits of As(V), MA, DMA, AB, TMAO, AC and TMI obtained with the optimized HPLC-N2-MIP-MS system were 0.68, 0.95, 2.01, 0.92, 22.1, 1.31 and 1.75 µg l–1, respectively. The repeatability (RSD for three successive analyses) and reproducibility lRSD for three successive analyses performed on three different days) achieved were 0.7–9.22 and 6.5–11.4%, respectively, for the seven different arsenic compounds. No detectable spectroscopic interference of 40Ar35Cl+ was observed with a high chloride matrix (10 000 mg l–1). The developed HPLC-N2-MIP-MS method was successfully applied to the determination of arsenic compounds, principally AB, in NIES Candidate CRM-18 Freeze-Dried Human Urine (134 ± 6 µg l–1). The results agreed reasonably well with the HPLC-ICP-MS values.

Elemental Speciation Analysis by Multicapillary Gas Chromatography with Microwave-Induced Plasma Atomic Spectrometric Detection

Multicapillary column gas chromatography (MC-GC)/microwave-induced plasma atomic emission spectrometry (MIP AES) was developed for fast speciation analysis of organotin compounds in the environment. Ethylated butyltin compounds could be separated isothermally within less than 30 s (instead of ∼5-10 min) without sacrificing either the resolution or the sample capacity of conventional capillary GC with oven temperature gradient programming. Careful optimization of the pressure and temperature GC program allowed a comprehensive organotin speciation analysis including phenyltin compounds within less than 2.5 min, increasing the sample throughput 6-fold. Compatibility of MC-GC with an MIP atomic emission detector (MIP-AED) was discussed. MC-GC/MIP-AES was validated for the analysis of sediment (PACS-1 and BCR 462) and biological (NIES11) certified reference materials.

Applications of capillary electrophoresis in element speciation analysis of plant and food extracts

The performance of a new separation technique for metal-speciation — capillary electrophoresis (CE) — is presented. Polyhydroxy compounds such as polyphenols and organic tanning agents can be determined in the μg/L range. Certain complexes of these compounds with iron (III) ions may also be directly or indirectly verified. The work has shown that it is possible to determine certain complexes existing in beverages (tea and coffee) by decomplexation with chelating agents (CDTA). The ligands released can be separated by CE and identified by their migration time and UV/VIS absorption spectra.

Evaluation of sequential extraction for speciation of trace metals in model soil containing natural minerals and humic acid

A model soil synthesized with several natural minerals and humic acid is used to evaluate the sequential extraction for speciation analysis of trace elements in soil. Although the recommended sequential extractants are able to bring the individual geochemical phases into solution at the experimentally defined stage, none of the extractants is completely specific and efficient. Various proportions of metals released at exchangeable, carbonate-bound, Fe-Mn oxide-bound, organic-bound fractions are readsorbed onto the other solid geochemical phases during sequential extraction. However, it is difficult to quantify the extent of readsorption and/or redistribution for the individual element and for the individual geochemical phase.