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.     

Microchip Electrophoresis: A New Platform for Metal Speciation

Abstract

Metal speciation is of considerable interest to the scientific community, due to the significant roles played by individual metal species in biomedicine and in the environment. Microchip electrophoresis, as specifically applied to metal speciation, is reviewed here. The review covers microchip-based determinations of metal cations (directly), metal cations as complexed species using laser induced fluorescence, absorbance (LED) and chemiluminescence detection, oxidation states, and the speciation of simultaneously existing metal complex species. Rapid microchip analysis clearly opens up the potential for species distribution analysis of environmentally and biologically important metal complexes.     

Speciation of oxidation states of elements by capillary electrophoresis

Progress made in the last five years in the application of capillary electrophoresis methods to chemical speciation of elements is reported on the basis of over 100 literature references. The main trends observed include development of new on‐ and off‐capillary derivatization methods, application of new detection methods, and especially coupling of CE separation systems to powerful atomic spectroscopy and mass spectrometry instruments with various ionization techniques, providing either a sensitive element‐specific detection method or a third dimension for high performance separation. Besides numerous CZE and MEKC capillary electrophoresis methods only very few examples of CE speciation with capillary electrochromatography can be found. Concerning the chemical forms of elements determined, the new procedures developed are mostly focused on redox speciation of various oxidation states of elements, metal‐bound high molecular compounds, and organometallic species.     

毛细管电泳在形态分析中的应用

对近年来毛细管电泳（ＣＥ）与紫外检测器（ＵＶｄｅｔｅｃｔｏｒ）和ＣＥ与感应耦合等离子体质谱（ＩＣＰ－ＭＳ）联用在形态分析中的应用及其存在的一些问题加以评述。     

毛细管电泳用于形态分析

一种元素的生物可给性、环境行为和迁移性在很大程度上取决于它的形态。如不同的键合形式或氧化态，因此，作为元素物种鉴别和含量测定的形态分析变得越来越重要。毛细管电泳作为一种分离分析技术有许多优点可以满足形态分析的要求。本文从样品的预处理、毛细管电泳的修饰、进样方式、分离模式和检测等几个方面评述了毛细管电泳在形态分析中的应用。     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

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.     

磁性离子印迹技术用于元素形态分离分析

元素的形态决定了其在环境和生物过程中的不同行为,形态分析正在被分析化学、环境化学、地球化学、生态学、农学和生物医学等众多学科所关注。环境和生物样品基质复杂、化学形态多样、含量低且易转化是元素形态分析面临的挑战,因此对元素形态的甄别、定量、生态毒性评价和生理功能研究需要对原生形态进行高选择性识别和高效率分离。固相萃取是一种有效应对以上难题的方法,但现有材料和方法远不能满足要求。离子印迹聚合物可与印迹金属离子特异性结合,具有准确、灵敏、可靠的特点,近年来在元素形态分离富集和分析检测方面得到了较为广泛的应用。鉴于非磁性吸附剂在固相萃取操作时,需要将分散在样品溶液中的吸附材料经过离心或过滤分离,操作比较繁琐费时,而磁性材料易被外部磁场快速分离,因此操作简便快速的磁固相萃取正成为元素形态分离富集中一种极具潜力的方法。这篇综述系统总结了离子印迹技术的最新进展,包括离子印迹技术的原理、离子印迹聚合物的制备方法,并根据元素形态分析中离子印迹磁固相萃取的发展现状,分析了离子印迹技术所面临的挑战,最后对元素形态分析中离子印迹技术的未来发展方向和策略提出了建议,提出开发基于有机-无机杂化聚合的多功能磁性离子印迹纳米复合物用于样品的前处理是建立识别选择性高、分离能力强、吸附容量大、形态稳定性好的形态分析方法的一种重要举措。     

Trace metal and metalloid species determination: evolution and trends

Metal species determination has seen considerable evolution during the last decade. The issues addressed by total metal determinations using standard spectrochemical analyses deliver only a minimal amount of information required to appropriately inform decision making. In molecular analyses, coupled instrumentation systems allow us to obtain molecular information for assisting in identifying the compounds of interest. Metal species determinations will provide additional information beyond that available from total metal determinations. Many total metal determinations will be replaced with elemental speciation determinations when species-selective risk/benefit assessment is a priority. This paper discusses the differences between traditional inorganic metals analysis and metal species determinations and outlines new trends.     

碲的形态分析进展

综述了近年来国内外碲的无机、有机形态分析进展。因碲在环境样品中的含量低、分散,存在形式较多,建立快速、准确的碲形态分析方法是值得进一步探讨的问题。     

Solid phase microextraction as a tool for trace element speciation

Applications of solid phase microextraction (SPME) for trace element speciation are reviewed. Because of the relative novelty of the technique in the inorganic analytical field, the first part of this review provides a short overview of the principles of SPME operation; the second part describes typical SPME applications to elemental speciation. Volatile organometallic compounds can be collected by SPME from the sample headspace or liquid phase, directly or after derivatization. The usual separation method for the collected volatile species is gas chromatography. Non-volatile analyte species can be collected from the sample liquid phase and separated by liquid chromatography or capillary electrophoresis. Currently, most SPME applications in the inorganic field comprise analyte ethylation and headspace extraction followed by gas chromatographic separation of tin, lead and mercury species. The use of SPME for the study of equilibria in complex systems is also discussed and future roles of solid phase microextraction in the inorganic analytical field are raised.     

Conclusions of the workshop

The development of analytical techniques for the determination of chemical species has been one of the fastest growing features of the 90's in analytical chemistry. The need for good quality control of these determinations has led the Measurements and Testing Programme (BCR) to organize several series of interlaboratory studies in the field of speciation analysis over the last five years. The state of the art of speciation analysis was discussed at a first workshop in 1990 (Arcachon, F) and, at this stage, it was deemed necessary to discuss the progress achieved and the trends which should be developed in the near future. A workshop on Trends in Speciation Analysis was therefore held in Rome in February 1994, which allowed recommendations to be made based on round-table discussions. This paper gives a summary of these recommendations in the field of inorganic speciation. Projects currently undertaken in the field of inorganic speciation within the Measurements and Testing Programme are also described. An outline of the programme along with the panel of experts participating in this workshop is given in the appendix.     

Trace element speciation by ICP-MS in large biomolecules and its potential for proteomics

Latest studies on the chemical association of trace elements to large biomolecules and their importance on the bioinorganic and clinical fields are examined. The complexity of the speciation of metal-biomolecules associations in various biological fluids is stressed. Analytical strategies to tackle speciation analysis and the-state-of-the-art of the instrumentation employed for this purpose are critically reviewed. Hyphenated techniques based on coupling chromatographic separation techniques with ICP-MS detection are now established as the most realistic and potent analytical tools available for real-life speciation analysis. Therefore, the status and potential of metal and semimetals elemental speciation in large biocompounds using ICP-MS detection is mainly focused here by reviewing reported metallo-complexes separations using size-exclusion (SEC), ion-exchange (IE), reverse phase chromatography (RP) and capillary electrophoresis (CE). Species of interest include coordination complexes of metals with larger proteins (e.g. in serum, breat milk, etc.) and metallothioneins (e.g. in cytosols from animals and plants) as well as selenoproteins (e.g. in nutritional supplements), DNA-cisplatin adducts and metal/semimetal binding to carbohydrates. An effort is made to assess the potential of present trace elements speciation knowledge and techniques for "heteroatom-tagged" (via ICP-MS) proteomics.     

Conclusions of the workshop

The development of analytical techniques for the determination of chemical species has been one of the fastest growing features of the 90's in analytical chemistry. The need for good quality control of these determinations has led the Measurements and Testing Programme (BCR) to organize several series of interlaboratory studies in the field of speciation analysis over the last five years. The state of the art of speciation analysis was discussed at a first workshop in 1990 (Arcachon, F) and, at this stage, it was deemed necessary to discuss the progress achieved and the trends which should be developed in the near future. A workshop on Trends in Speciation Analysis was therefore held in Rome in February 1994, which allowed recommendations to be made based on round-table discussions. This paper gives a summary of these recommendations in the field of inorganic speciation. Projects currently undertaken in the field of inorganic speciation within the Measurements and Testing Programme are also described. An outline of the programme along with the panel of experts participating in this workshop is given in the appendix.     

Capillary electrophoresis inductively coupled plasma mass spectrometry

Chemical speciation (extraction of elemental information and identification of molecular environment for an analyte in a complex sample) has been a long sought after goal for analytical chemists. Recently, because of successful developments in more sensitive element-specific detectors and gentle separation schemes, which preserve the true chemical information in a real sample, routine speciation experiments are becoming a common occurrence in the scientific literature. For many reasons, the combination of capillary electrophoresis (for separation of different chemical species) with inductively coupled plasma mass spectrometry (for element and isotope specific detection) has emerged as the method of choice for these analyses. In this article the basic principles of capillary electrophoresis inductively coupled plasma mass spectrometry are discussed. Design consideration for instrument interface, anticipated difficulties with speciation experiments and applications for specific matrices and analytes are also presented in this article.     

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).     

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.     

The role of element speciation in environmental and occupational medicine

In order to evaluate the interaction with the environment or to assess absorption, binding mechanisms, reactivity and excretion of elements in humans, element speciation can provide more information than the analysis of element as a whole. Some examples that confirm the importance of speciation depend on the choice of the most appropriate indicator or representative matrix. The determination of As(III), As(V), monomethylarsonic and dimethylarsinic acids can be used to evaluate occupational exposure to As. Exposure to inorganic Hg should be measured by its content in urine, whereas in the case of exposure to alkyl Hg, blood and hair should be considered. Speciation may also be useful in studying element toxicokinetics, since it is well known that hexavalent Cr is taken up more than the trivalent form, and that species of the same metal are differently partitioned in blood. Pentavalent forms of As are absorbed more than trivalent forms, and the organic species of elements are excreted faster than inorganic species. In addition, speciation can play an important role in assessing element toxicodynamics. The toxicity of the three oxidation states of Hg differs considerably; for As a decreasing toxicity from arsenite to dimethylarsinic acid is proposed; for organotin compounds, higher toxicity for ethyl groups than for phenyl groups is reported. However, speciation in biological media is difficult when applied to other elements because of the lack of information on the existence and significance of species whose determination could be valuable. Furthermore, there may be no analytical methods that allow an accurate measurement of the species. The feasibility of speciation in occupational and environmental medicine depends mainly on our capability to solve some problems related to the identification and determination of species and on the demonstration that species measurement represents a clear improvement compared to total element determination.     

Trace element analytical speciation in biological systems: importance,challenges and trends

Speciation of trace elements is a relatively new field and it was in toxicology that the relationship between the chemical form of a metal and its harmful effects was first recognized. The present need for chemical speciation information in biochemistry bioinorganic and clinical chemistry is documented in an attempt to justify the present demand for innovative chemical speciation strategies and analytical technologies.The challenge and complexity of speciation is stressed and three different categories of analytical speciation of increasing analytical difficulty are proposed. Analytical strategies developed so far to try to tackle speciation problems (computational approaches, direct species-specific and hybrid techniques) are reviewed and critically assessed for biological materials. It is indisputable these days that in most cases of real-life analytical speciation we have to resort to the development and use of hybrid techniques combining an adequate separation technique for the species physical separation and an element specific detector such as those based in atomic spectrometry. Examples of such strategies, as developed mainly in the author's laboratory and including chromatographic and non-chromatographic type hybrid strategies coupled to flame, plasma and electrothermal vaporization atomic detectors, are discussed in more detail.Finally, in light of the latest trends observed in this new field, the author attempts to cast a forward look into the foreseeable future of analytical speciation research in biological and biomedical sciences. The urgent plea for quality assurance in non-routine analysis and the concept of using complementary analytical techniques and definitive methods to attack the complexity of chemical speciation in biological systems are particularly highlighted.