Handbook of Elemental Speciation, 2 Volume Set - Hardcover

Hardcover

ISBN 10: 0470014652 ISBN 13: 9780470014653

Publisher: Wiley, 2005

Synopsis

This two-volume handbook, prepared by Editors involved in an EU validation project on speciation, provides comprehensive coverage of the sample preparation methods and analytical techniques utilised for speciation of different elements in environmental, food, and clinical samples.
Handbook of Elemental Speciation I - Techniques and Methodology brings together a collection of chapters covering different aspects of procedures for speciation analysis at the different levels starting from sample collection and storage, through sample preparation approaches to render the species chromatographable, principles of separation techniques used in speciation analysis, to the element specific detection. Also covers quality assurance and risk assessment, and speciation-relevant legislation.
Handbook of Elemental Speciation II - Species in the Environment, Food, Medicine and Occupational Health provides a comprehensive, cross-disciplinary presentation of the analytical techniques involved in speciation.
* Comprehensive coverage of key elements and compounds in situ
* Addresses the analysis and impact of these elements and compounds, e.g. arsenic, lead, copper, iron, halogens, etc., in food, the environment, clinical and occupational health
* Detailed methodology and data are reported, as well as regulatory limits
* Includes general introduction on the impact in these key areas

About this title

About the Author

Rita Cornelis and Joseph A. Caruso are the authors of Handbook of Elemental Speciation, 2 Volume Set, published by Wiley.

Excerpt. © Reprinted by permission. All rights reserved.

Handbook of Elemental Speciation, 2 Volume Set

By Rita Cornelis

John Wiley & Sons

Copyright © 2005 Rita Cornelis
All right reserved.
ISBN: 9780470014653

Chapter One

Introduction

R. C. Cornelis Laboratory for Analytical Chemistry, Ghent University, Belgium

H. M. Crews Central Science Laboratory, Sand Hutton, York, UK

J. A. Caruso University of Cincinnati, Ohio, USA

K. G. Heumann Institut fur Anorganische and Analytische Chemie, Mainz, Germany

1 Definition of Elemental Speciation and of Fractionation 2

2 Problems to be Solved 2

3 Speciation Strategies 3

4 References 5

'Speciation', a word borrowed from the biological sciences, has become a concept in analytical chemistry, expressing the idea that the specific chemical forms of an element should be considered individually. The underlying reason for this is that the characteristics of just one species of an element may have such a radical impact on living systems (even at extremely low levels) that the total element concentration becomes of little value in determining the impact of the trace element. Dramatic examples are the species of tin and mercury, to name just these two. The inorganic forms of these elements are much less toxic or even do not show toxic properties but the alkylated forms are highly toxic. No wonder analytical chemists had to study elemental speciation and devise analytical techniques that produce qualitative and quantitative information on chemical compounds that affect the quality of life.

Before embarking on the definitions of elemental speciation and species, it may be interesting to give a short historical setting of this emerging branch of analytical chemistry. Analytical chemistry began as a science in the early 19th century. A major milestone was the book by Wilhelm Ostwald 'Die Wissenschaftlichen Grundlagen der analytischen Chemie' (Scientific Fundamentals of Analytical Chemistry) in 1894 [1]. A personality who contributed substantially to the development of analytical chemistry and chemical analysis was Carl Remigus Fresenius. In 1841 he published a very interesting book on qualitative chemical analysis [2]. It was followed over the next 100 years by a series of standard works on qualitative and quantitative analysis by several generations of the Fresenius family and by the publications by Treadwell [3, 4], Feigl [5] and Kolthoff [6, 7], to name just these few. The interest remained largely focused on inorganic analytical chemistry. The term 'trace elements' dates back to the early 20th century, in recognition of the fact that many elements occurred at such low concentrations that their presence could only just be detected. During the following 60 years all efforts were focused on total trace element concentrations. Scientists developed methods with increasing sensitivity. It was only in the early 1960s that questions were raised concerning the chemical form of the trace elements and that the need for an analytical methodology developed subsequently. This development has been growing exponentially to the point that research on trace element analysis today appears almost exclusively focused on trace element species.

Extensive literature is available on the speciation and fractionation of elements. Newcomers have to absorb a wealth of highly specialised publications and they miss the broader overview to guide them. This handbook aims to provide all the necessary background and analytical information for the study of the speciation of elements.

The objective of this handbook is to present a concise, critical, comprehensive and systematic (but not exhaustive), treatment of all aspects of analytical elemental speciation analysis. The general level of the handbook makes it most useful to the newcomers in the field, while it may be profitably read by the analytical chemist already experienced in speciation analysis.

1 DEFINITION OF ELEMENTAL SPECIATION AND OF FRACTIONATION

The International Union for Pure and Applied Chemistry (IUPAC) has defined elemental speciation in chemistry as follows:

(i) Chemical species. Chemical element: specific form of an element defined as to isotopic composition, electronic or oxidation state, and/or complex or molecular structure.

(ii) Speciation analysis. Analytical chemistry: analytical activities of identifying and/or measuring the quantities of one or more individual chemical species in a sample.

(iii) Speciation of an element; speciation. Distribution of an element amongst defined chemical species in a system.

When elemental speciation is not feasible, the term fractionation is in use, being defined as follows:

(iv) Fractionation. Process of classification of an analyte or a group of analytes from a certain sample according to physical (e.g., size, solubility) or chemical (e.g., bonding, reactivity) properties.

As explained in the IUPAC paper [8], it is often not possible to determine the concentrations of the different chemical species that sum up to the total concentration of an element in a given matrix. Often, chemical species present in a given sample are not stable enough to be determined as such. During the procedure, the partitioning of the element among its species may be changed. For example, this can be caused by a change in pH necessitated by the analytical procedure, or by intrinsic properties of measurement methods that affect the equilibrium between species. Also in many cases the large number of individual species (e.g., in metal-humic acid complexes or metal complexes in biological fluids) will make it impossible to determine the exact speciation. The practice is then to identify various classes of the elemental species.

2 PROBLEMS TO BE SOLVED

While the incentive to embark on speciation and fractionation of elements is expanding, it becomes more and more evident that the matter has to be handled with great circumspection. Major questions include: What are the species we want to measure? How should we sample the material and isolate the species without changing its composition? Can we detect very low amounts of the isolated species, which may represent only a minute fraction of the total, already ultra-trace element concentration? How do we calibrate the species, many of these not being available as commercial compounds? How do we validate methods of elemental analysis? All of these questions will be carefully dealt with in the first volume of the handbook. The second and third volumes will extensively address elemental species of specific elements and the analysis of various classes of species.

Advances in instrumentation have been crucial to the development of elemental speciation. There has been a very good trend towards lower and lower detection limits in optical atomic spectrometry and mass spectrometry. This has allowed the barrier between total element and element species to be crossed. While the limit of detection for many polluting species is sufficient for their measurement in a major share of environmental samples, this is not yet the case for human, animal and perhaps plant samples at 'background levels'. The background concentration of elemental species of anthropogenic origin was originally zero. Today they are present, because they have been and continue to be distributed in a manner that affects the life cycle. However, because we cannot measure them in living systems it does not mean that their presence is harmless. At the same time it is also highly plausible that a certain background level of these anthropogenic substances can be tolerated without any adverse effect. In order to assess the impact of low background levels of element species we will have to develop separation and detection techniques that surpass the performance of the existing speciation methodology.

In the mean time research teams are very resourceful in developing computer controlled automated systems for elemental speciation analysis. These are or will become tremendous assets for routine analyses. Preferably systems should be simple, robust, low cost and if at all possible portable, to allow for fieldwork. Although currently limited it can be postulated that once there are more regulatory or economic motives, this technology would develop rapidly. Moreover, sensors will play a major role in rapid detection of elemental species. Simple screening methods will be increasingly popular because they can provide speedy and reliable tests to detect elemental species and give an estimate of their concentration.

Good laboratory practice and method validation are a must to produce precise and accurate results. To this end, it is evident that provision has to be made for elemental species data in more certified reference materials (CRMs) reporting on elemental species. This need will become even more acute once legislation becomes specific and cites elemental species instead of the total concentration of the element and its compounds, as is presently the general rule. This type of legislation may be politically charged, because every species carries a different health risk or benefit. The toxicity may vary by several orders of magnitude among species of the same element. This may lead to some confusing and dangerous conclusions. A product may be legally acceptable on the basis of total concentration but when that total consists of some very toxic species it may constitute a real hazard. The opposite may also be true. This can be exemplified by the occurrence of arsenic in food. Whereas the total arsenic in some fish derivatives, such as gelatine, often exceeds the accepted limit, the product should not be rejected, because the arsenic is mainly present as arsenobetaine, a non-toxic arsenic species, as opposed to the toxic inorganic arsenic species.

3 SPECIATION STRATEGIES

'Strategy' signifies 'a careful plan or method' or 'the art of devising or employing plans or stratagems toward a goal' [9]. Ideally scientists hope to learn everything about the elemental species they study: to start with its composition, its mass, the bio- and environmental cycle, the stability of the species, its transformation, and the interactions with inert or living matter. This list is not exhaustive. The work involved to achieve this goal is, however, challenging, if not impossible to complete. Therefore a choice has to be made to identify the most important issues as elemental speciation studies are pursued. A first group of compounds to be studied very closely are those of anthropogenic origin. Although they fulfil the requirements for which they were synthesised, unless they happen to be synthetic by-products or waste, their long-term effect on the environment, including living systems, has often been ignored or misjudged. One of the most striking examples is the group of organotin compounds. They have surely proven to be the most effective marine anti-fouling agents, fungicides, insecticides, bacteriostats, PVC stabilising agents, etc. However, the designers of these compounds never anticipated what the negative effect would be on the environment. Their disturbing impact on the life cycle of crustaceans constituted the first alarming event. In the mean time these components have become detectable, with concentrations now increasing in fish products and even in vegetables from certain areas. Little thought was given that organotin compounds would be serious endocrine disruptors, or that they would have such a long half-life. Hence they will continue to be a burden on the environment and ultimately on mankind itself into the distant future. The organotin compounds are only a minute part of the total amount of tin (mainly inert tin oxides) to be found in contaminated areas. Determination of the total tin concentration would surely not be appropriate.

In speciation studies, a lot of attention must be paid to the stability. Species stability depends on the matrix and on physical parameters, such as temperature, humidity, UV light, organic matter, etc. Next comes the isolation and purification of the species, the study of the possible transformation through the procedure, their characteristics and interactions. New analytical procedures have to be devised, including appropriate quantification and calibration methodologies.

Besides the suspect elemental species of anthropogenic origin, there is the barely fathomable domain of the species that developed along with life on earth. For many elements nothing is really known, or only a few uncertain facts can be stated. Whereas the total trace element concentration may be static, the species may be highly dynamic. They will change continuously with respect to changes in the surrounding environment, depending on chemical parameters such as pH value or concentration of potential ligands for complex formation, the physiological state of a cell, and state of health of a living entity. Therefore, thermodynamic but also kinetic stability of elemental species in the environment has to be taken into account. Unstable species in the atmosphere are predominant and this steady transformation requires special analytical procedures. Although species in living cells can be stable covalent compounds when the element forms the core of the molecule (such as Co in vitamin [B.sub.12]), most elemental species exhibit very low stability constants with their ligands. These compounds are, however, very active in reaching the target organs. This to say that a reliable speciation strategy will include stability criteria for the species and awareness of possible transformations.

Understanding the fate of the trace elements in the life cycle is of paramount importance. When, through natural or anthropogenic activities, metal ions enter the environment and the living systems, only a small fraction will remain as the free ion. The major share will be complexed with either inorganic or organic ligands. Natural methylation of metal ions under specific conditions is prevalent. The new species can be much more toxic, as is the case with methylated mercury, or less toxic as in the case of arsenic. In the case of mercury, the concentration of ionic mercury in water may be very low (a few ng [L.sup.-1] )and that of methylmercury only 1% of total Hg. Unfortunately, this accumulates to mg [kg.sup.-1] levels in the top predators of the food chain, with methylmercury making up 90 to 100 % of the total Hg concentration. Metal ions will also be incorporated into large molecular structures such as humic substances. Elucidation of the many, often-labile species will take many more years. Trace element speciation has become important in all fields of life, and concerns industry, academia, government and legislative bodies [10].

It is obvious that it would have been impossible to accomplish the stated aims and objectives of this handbook without the wholehearted cooperation of the distinguished authors who contributed the various chapters. To them we express our sincere appreciation and gratitude.

Continues...

Excerpted from Handbook of Elemental Speciation, 2 Volume Setby Rita Cornelis Copyright © 2005 by Rita Cornelis. Excerpted by permission.
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Edition details

• Publisher: Wiley
• Publication date: 2005
• Language: English
• ISBN 10: 0470014652
• ISBN 13: 9780470014653
• Binding: Hardcover
• Edition number: 1
• Number of pages: 1458
• Editor: Cornelis Rita