Über die Autorin bzw. den Autor

John R. Dean took his first degree in Chemistry at UMIST, followed by an M.Sc. in Analytical Chemistry and Instrumentation at Loughborough University of Technology and finally a Ph.D. and D.I.C. in Physical Chemistry at Imperial College. He then spent 2 years as a postdoctoral research fellow at the Food Science Laboratory of the Ministry of Agriculture, Fisheries and Food in Norwich in conjunction with Polytechnic South West in Plymouth. The work was focused on the development of directly coupled high performance liquid chromatography inductively coupled plasma mass spectrometry methods for trace element speciation in foodstuffs. This was followed by a temporary lectureship in Inorganic Chemistry at Huddersfield Polytechnic. In 1988 he was appointed to a lectureship in Inorganic/Analytical Chemistry at Newcastle Polytechnic (now Northumbria University). This was followed by promotion to Senior Lecturer (1990), Reader (1994) and Principal Lecturer (1998). In 1998 he was awarded a D.Sc. (London) in Analytical and Environmental Science and was the recipient of the 23rd SAC Silver Medal in 1995. He has published extensively in analytical and environmental science. He is an active member of the Royal Society of Chemistry Analytical Division having served as a member of the atomic spectroscopy group for 15 years (10 as honorary secretary) as well as a past chairman (1997-99). He has served on Analytical Division council for three terms and is currently its vice-president (2002-04) as well as chairman of the North East Region (2001-03).

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This text provides a valuable and readily accessible, practical introduction to inductively coupled plasma spectroscopy, serving both as a basic textbook for taught courses and also as a ‘self-study’ resource for those pursuing ‘open learning/distance learning’ forms of study.

Topics covered within this essential text include:

• Methodology for trace elemental analysis
• Sample preparation techniques for inductively coupled plasma spectroscopy, including those used for aqueous and solid samples, plus details of the various extraction procedures that can be used to prepare samples
• Sample introduction procedures for plasma sources
• The inductively coupled plasma and other sources used for atomic emission spectroscopy and mass spectrometry
• Fundamental aspects of atomic emission spectroscopy and mass spectrometry
• Spectrometers and detectors used for plasma spectroscopy
• Interferences in atomic emission spectroscopy
• Principles of inductively coupled plasma–mass spectrometry (ICP–MS)
• Types of mass spectrometers used for ICP–MS
• Interferences in ICP–MS and their remedies, including collision/reaction cells
• Isotope dilution analysis
• A range of applications for this technique, including forensic science, industrial analysis, clinical/biological analysis, materials analysis, environmental analysis, food analysis and pharmaceutical analysis
• Sample data sheets that can be used to record information in the laboratory
• A comprehensive bibliography, providing information on how to keep up-to-date with the latest developments in this field, guiding the reader to more specialized texts and sources, including books, journals and recommended web sites

Practical Inductively Coupled Plasma Spectroscopy will be invaluable to those students studying at Foundation and BTEC (HNC and HND) levels, and for those pursuing BSc, MChem, MSc and MRes courses in analytical chemistry, as well as subsidiary courses in life, environmental and food science. In addition, it will be a useful guide to those using ICP, and related techniques, in applied research and analysis.

Aus dem Klappentext

This text provides a valuable and readily accessible, practical introduction to inductively coupled plasma spectroscopy, serving both as a basic textbook for taught courses and also as a ‘self-study’ resource for those pursuing ‘open learning/distance learning’ forms of study.

Topics covered within this essential text include:

• Methodology for trace elemental analysis
• Sample preparation techniques for inductively coupled plasma spectroscopy, including those used for aqueous and solid samples, plus details of the various extraction procedures that can be used to prepare samples
• Sample introduction procedures for plasma sources
• The inductively coupled plasma and other sources used for atomic emission spectroscopy and mass spectrometry
• Fundamental aspects of atomic emission spectroscopy and mass spectrometry
• Spectrometers and detectors used for plasma spectroscopy
• Interferences in atomic emission spectroscopy
• Principles of inductively coupled plasma–mass spectrometry (ICP–MS)
• Types of mass spectrometers used for ICP–MS
• Interferences in ICP–MS and their remedies, including collision/reaction cells
• Isotope dilution analysis
• A range of applications for this technique, including forensic science, industrial analysis, clinical/biological analysis, materials analysis, environmental analysis, food analysis and pharmaceutical analysis
• Sample data sheets that can be used to record information in the laboratory
• A comprehensive bibliography, providing information on how to keep up-to-date with the latest developments in this field, guiding the reader to more specialized texts and sources, including books, journals and recommended  web sites

Practical Inductively Coupled Plasma Spectroscopy will be invaluable to those students studying at Foundation and BTEC (HNC and HND) levels, and for those pursuing BSc, MChem, MSc and MRes courses in analytical chemistry, as well as subsidiary courses in life, environmental and food science. In addition, it will be a useful guide to those using ICP, and related techniques, in applied research and analysis.

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Practical Inductively Coupled Plasma Spectroscopy

John Wiley & Sons

Chapter One

Learning Objectives

To be aware of the different types of contamination that can cause problems in trace elemental analysis.

To be aware of a whole range of terms and definitions as used in analytical chemistry.

To appreciate the range of units used in analytical chemistry.

To be able to present numerical data with correct units, and be able to interchange the units as required.

To be able to present data in the form of a table.

To be able to present data in the form of a graph.

To be able to determine the concentration of an element from a straight line graph using the equation y = mx + c.

To be able to calculate the dilution factor for a liquid sample and a solid sample, and hence determine the concentration of the element in the original sample.

To appreciate the concept of quality assurance in the analytical laboratory.

To be aware of the significance of certified reference materials in elemental analysis.

1.1 Introduction

Trace elemental analysis requires more than just knowledge of the analytical technique to be used - in this case, inductively coupled plasma spectroscopy. This requires knowledge of a whole range of disciplines that need to come together to create the final result. The disciplines required can be described as follows:

sampling, sample storage and preservation, and sample preparation methodologies

analytical technique

data control, including calibration strategies and the use of certified reference materials for quality control

data management, including reporting of results and their meaning

While most of these are covered to some extent in this book, the reader should also consult other resources, e.g. books. Suggestions for further study are given in Chapter 8.

The perspective that is required when faced with trace element analysis are the additional precautions required in terms of management of contamination, choice of reagents and acids, and cleanliness of the workspace. For example, the grade of chemical used to prepare calibration standards is a major concern when working at trace element analysis levels (sub-?g [ml.sup.-1]). Chemicals are available in a range of grades from 'GPR - general purpose reagent' through to, for example, 'AnalaRR - analytical reagent'. However, the descriptor does not identify that the chemical is any purer (the purity is often given on the bottle, e.g. 99.8%), but identifies the amount of effort that the manufacturer has gone to in the preparation of the chemical. For 'AnalaRR' grade materials, the manufacturer has characterized the chemical by subjecting it to chemical analysis. This additional effort is then passed on to the customer in the form of a higher price. The use of sample blanks in the analytical procedure is essential to identify 'problem elements'.

The risk of contamination is a major problem in trace element analysis. Apart from the analytical reagent used to prepare standards, as discussed above, contamination can also be experienced from sample containers, e.g. volumetric flasks, pipettes, etc. For example, metal ions can adsorb onto glass containers and then leach into the solution under acidic conditions, thereby causing contamination. This can be minimized by cleaning the glassware prior to use by soaking for at least 24 h in a 10% nitric acid solution, followed by rinsing with 'clean' deionized water (three times).

DQ 1.1 What type of water would you consider to be clean?

Answer

Drinking water, commercially bottled drinking water or laboratory distilled water. The actual answer depends to some extent on the work to be carried out. For trace element analysis, it is possible to purchase commercial systems that filter (distilled) water through a combination of ion-exchange columns to remove trace element impurities.

The cleaned vessels should then either be stored upside down or covered with ClingfilmR to prevent dust contamination.

The individual working in the laboratory is also a major source of contamination. Therefore, as well as the normal laboratory safety associated with wearing a laboratory coat and safety glasses, it may be necessary to take additional steps such as the wearing of 'contaminant-free' gloves and a close-fitting hat.

1.2 Analytical Terms and their Definitions

The following is an alphabetical list of the most important analytical terms of use in practical inductively coupled plasma spectroscopy.

Accuracy A quantity referring to the difference between the mean of a set of results or an individual result and the value which is accepted as the true or correct value for the quantity being measured.

Acid digestion Use of acid (and often heat) to destroy the organic matrix of a sample to liberate the metal content.

Aliquot A known amount of a homogenous material assumed to be taken with negligible sampling error.

Analyte The component of a sample which is ultimately determined directly or indirectly.

Bias Characterizes the systematic error in a given analytical procedure and is the (positive or negative) deviation of the mean analytical result from the (known or assumed) true value.

Calibration The set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument or measuring system and the corresponding known values of the measurand.

Calibration curve Graphical representation of a measuring signal as a function of quantity of analyte.

Certified Reference Material (CRM) Reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes its traceability to an accurate realization of the units in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence.

Complexing agent The chemical species (an ion or a compound) which will bond to a metal ion using lone pairs of electrons.

Confidence interval Range of values that contains the true value at a given level of probability. The latter is known as the confidence level.

Confidence limit The extreme values or 'end-values' in a confidence interval.

Contamination In trace analysis this is the unintentional introduction of analyte(s) or other species which are not present in the original sample and which may cause an error in the determination. This can occur at any stage in the analysis. Quality assurance procedures, such as analyses of blanks or of reference materials, are used to check for contamination problems.

Control of Substances Hazardous to Health (COSHH) Regulations that impose specific legal requirements for risk assessment wherever hazardous chemicals or biological agents are used.

Co-precipitation The inclusion of otherwise soluble ions during the precipitation of lower-solubility species.

Dilution factor The mathematical factor applied to the determined value (data obtained from a calibration graph) which allows the concentration in the original sample to be determined. Frequently, for...