- Email: [email protected]
Laser-enhanced ionisation spectrometry
292
trends in analytical chemistty, vol. 16, no. 5, 1997
[ lo] S.B.O. Adeloju, F. Pablo, Anal. Chim. Acta 270 (1992) 143. [ 111 C.M.A. Brett, A.M.C.F. Oliveira Brett, J.L. Pereira, Electroanalysis 3 ( 199 1) 683. [ 121 H. Huang, H. Chi, D. Jagner, L. Renman, Anal. Chim. Acta 208 (1988) 237. [ 13 ] M.A. Malone, A. Costa Garcia, P. Tunon Blanco, M.R. Smyth, Analyst 118 (1993) 649. [ 141 A. Economou, P.R. Fielden, A.J. Packham, Analyst 119 (1994) 279. [ 151 C. Hua, D. Jagner, L. Renman, Anal. Chim. Acta 197 (1987) 265. [ 161 A. Economou, P.R. Fielden, Analyst 118 ( 1993) 47. ]171 H. Eskilsson, C. Haraldsson, D. Jagner, Anal. Chim. Acta 175 (1985) 79. 1181 M.A. Malone, A. Costa Garcia, P. Tunon Blanco, M.R. Smyth, Anal. Methods Instrum. 1 ( 1993) 164. ]191 J.Y. Wang, J. Wang, J.M. Lu, K. Olsen, Anal. Chim. Acta 292 (1994) 91. ]201 A. Economou, P.R. Fielden, Analyst 118 ( 1993) 1399. 1211 M.M.P.M. Neto, M.M.G.S. Rocha, C.M.A. Brett, Talanta 41 (1994) 1597. 7 1221 S.B. Adeloju, P. Fleurdelis, Electroanalysis ( 1995 ) 476. ]231 J. Wang, B.M. Tian, Anal. Chim. Acta 270 ( 1992) 137.
[ 241 H. Braun, M. Metzger, Fresenius Z. Anal. Chem. 318 (1984) 321. [ 251 H.J. Diederich, S. Meyer, F. Scholz, Fresenius Z. Anal. Chem. 349 (1994) 670. [ 261 C. Hua, D. Jagner, L. Renman, Talanta 35 ( 1988) 597. [ 27 ] G.M. Greenway, G. Wolfbauer, Anal. Chim. Acta 312 (1995) 15. [ 28 ] C. Hua, D. Jagner, L. Renman, Talanta 35 ( 1988) 525. [ 291 J. Amel de1 Pozo, A. Costa Garcia, A.J. Miranda Ordieres, P. Tunon Blanco, Electroanalysis 4 (1992) 87. [ 301 J. Amel de1 Pozo, A. Costa Garcia, P. Tunon Blanco, Anal. Chim. Acta 289 (1994) 169. [ 311 M. Pedrero, B. Casado, F.J. ManueldeVillena, J.M. Pingarron, Fresenius Z. Anal. Chem. 349 (1994) 546. [ 321 W.H. Chart, H. Huang, Analyst 121 (1996) 1727.
Anastasios Economou is a postdoctoral research associate in the Depaltment of Chemistry, Laboratory of Analytical Chemistry University of Athens, Panepistimiopolis, Athens 157 71, Greece. Peter R. Fielden is a senior lecturer in the Department of instrumentation and Analytical Science, UMIST, PO Box 88, Manchester M60 IQD, UK.
book reviews Laser-enhanced
ionisation spectrometry
Laser-Enhanced lonisation Spectrometry, J.C. Travis and G.C. Turk, 1996, xi + 334 pages, ISBN 0-47157684-0.
This latest volume to the Chemical Analysis series of publications will provide an invaluable reference to accomplished researchers in the field of laser-enhanced ionisation (LEI) and to students alike, who may only be beginning their research in this fascinating subject. Indeed, this publication allows one to quickly become familiar with the basic principles of LEI within the first chapter, with real applications and instrumentation also being targeted at later stages. Optical
techniques such as LEI are being increasingly considered as viable alternatives to traditional methods of measurement within industry, and it is due to the emphasis that is placed on the practical issues involved in the technique that will make this book attractive to industrialists and academics alike. The publication takes you carefully through the fundamental issues relating to weakly ionised plasmas and the subsequent behaviour of the plasmas following excitation from a laser source which is tuned to a particular atomic transition. Issues such as ionisation efficiency, two-photon excitation and Stark broadening are considered, with experimental find-
ings and the developed theory being compared. The particular aspect which was most pleasing was the way in which sight was never lost of the practical issues surrounding the theory, and the logical approach in which the theory was built up from first principles. The authors fully acknowledge that the results produced by the various models do not correspond exactly to experiment. A most useful discussion is given which highlights the practical aspects of LEI which can lead to a deviation from the predicted behaviour. In fact, throughout the highly theoretical argument, the authors still manage to retain a practical bias, with the benefits of modern solid-state cw tuneable lasers highlighted as well as other potential improvements to the technique.
trends in analytical
XI
chemistry, vol. 16, no.5, 1997
account of the noise problems introduced by radio frequency interference common with this type of laser. Further practical issues such as electronic circuitry (filtering) and pre-amplification, noise characteristics and how to reduce their effects and limits of detection for the technique are also discussed. The authors conclude that this technique is amongst the most sensitive available for trace element analysis although there are still a number of problems since it is susceptible to many background interferences. For the future such a technique will be in direct competition with the ICP-MS system, already widely used in industry.
The basic instrumental configurations that have evolved over the years are also described. In general the discussion is presented in a clear and concise manner following logical steps through an LEI system from the atomisation stage to signal display. Different types of flame, e.g. air/acetylene, air/hydrogen etc., are discussed with relation to the issue of flame background ionisation. Mention is also made of other techniques using higher temperature plasmas where it is pointed out that LEI is more specific in its excitation. The discussion also describes the different laser pumping sources for the tuneable dye lasers preferred. Here the arguments for cw and pulsed lasers are clearly laid out centering on the excitation efficiency and how this can be optimised for differing laser irradiances, pulse lengths and repetition rates. The conclusion, that pumping via XeCl excimer lasers is preferred, is explained whilst taking
ANDREW
I. WHITEHOUSE
DI: A.I. Whitehouse is at the Optics and Photonics Group, BNFL UK Group, Sellafield, Seascale, Cumbria, CA20 IPG, UK.
-
Dietary fi bre analysis Dietary fibre analysis, by D.A.7: Southgate, RSC Food Analysis Monographs (Series editor t? S. Belton), 174 pages, 1995, ISBN 085404556-2 A good starting point when writing a book on analytical chemistry is to have the targeting compound or group of compounds well defined, and to use this basic information in an objective discussion of the performance of the various analytical methods. With dietary fibre it is not that simple as no general agreement has yet been reached about the very definition of dietary fibre and thus how it can be measured. The author consequently asks himself why write a practical handbook in an area where there is still so much dispute over even the most basic issues ? Fortunately the author convinced himself that there are justifiable reasons to write a book in his specialised area and can be satisfied with the outcome of the book which provides useful information for all analysts confronted with the difficult task of doing dietary fibre ana-
lysis. The book consists of eight chapters covering: the dietary fibre hypothesis, the chemistry of dietary fibre, analytical strategies, sampling and analytical quality assurance, the total dietary fibre method, the non-starch polysaccharide methods, other analytical methods for dietary fibre and its components and choice of analytical methods. In addition, the book contains an Appendix covering the preparation of in-house reference materials and a description of ANALOP, a system for identifying critical stages in an analytical protocol and quantifying their importance. The three first chapters give a good background and understanding of how the analytical techniques for measuring dietary fibre have evolved. Three major analytical approaches that have contributed to the development of current methods are discussed. The first group of methods derives from the analysis of the plant cell wall, the second group of methods derives from the analysis of the indigestible components in animal feeds and human foodstuffs, whilst the third
group of methods originates from the nutritional research environment. It is stressed that with no universally agreed definition an essential task of the analyst in designing analytical protocols is to make clear the purpose of the analyses. Although it may appear trivial the first and most crucial step in producing sound analytical data is the taking of a representative sample and its preparation. The author describes the various steps in the development of sampling protocols. He stresses that in the case of dietary fibre (and some other constituents) the requirement for a representative sample is slightly different depending on the purpose of the analysis, e.g. physiological studies, data bases, labelling, etc. The value of using certified and in-house reference materials to ensure the quality of the analytical results is further highlighted. The evolution of the two major methods for dietary fibre analysis the enzymatic-gravimetric total dietary fibre (TDF) method and the enzymatic-chemical non-starch polysaccharide (NSP) method are described in details in two chapters. These chapters are central and provide the reader with a good understanding of their different origins and backgrounds and how they have evolved in response to weaknesses identified in collaborative trials. Both methods have. undergone extensive collaborations, and details from these trials are discussed thoroughly. The author further assesses the methods by ANALOP to identify potential causes of imprecision and inaccuracy. It is striking that in spite of numerous improvements aimed at making the two types of methods more precise and robust, the methods are still not considered adequate for regulatory use because of their relatively poor precision and performance within and between laboratories. In addition to these two major groups of dietary fibre methods a separate chapter covers other methods that have been proposed for measurements of dietary fibre and its components. These include methods deriving from the chemistry of the plant cell wall, studies of the indigestibility components in foods and studies on the composition of food carbohydrates. Compared with the TDF and NSP
trends in analytical chemistty, vol. 16, no. 5, 1997
[ lo] S.B.O. Adeloju, F. Pablo, Anal. Chim. Acta 270 (1992) 143. [ 111 C.M.A. Brett, A.M.C.F. Oliveira Brett, J.L. Pereira, Electroanalysis 3 ( 199 1) 683. [ 121 H. Huang, H. Chi, D. Jagner, L. Renman, Anal. Chim. Acta 208 (1988) 237. [ 13 ] M.A. Malone, A. Costa Garcia, P. Tunon Blanco, M.R. Smyth, Analyst 118 (1993) 649. [ 141 A. Economou, P.R. Fielden, A.J. Packham, Analyst 119 (1994) 279. [ 151 C. Hua, D. Jagner, L. Renman, Anal. Chim. Acta 197 (1987) 265. [ 161 A. Economou, P.R. Fielden, Analyst 118 ( 1993) 47. ]171 H. Eskilsson, C. Haraldsson, D. Jagner, Anal. Chim. Acta 175 (1985) 79. 1181 M.A. Malone, A. Costa Garcia, P. Tunon Blanco, M.R. Smyth, Anal. Methods Instrum. 1 ( 1993) 164. ]191 J.Y. Wang, J. Wang, J.M. Lu, K. Olsen, Anal. Chim. Acta 292 (1994) 91. ]201 A. Economou, P.R. Fielden, Analyst 118 ( 1993) 1399. 1211 M.M.P.M. Neto, M.M.G.S. Rocha, C.M.A. Brett, Talanta 41 (1994) 1597. 7 1221 S.B. Adeloju, P. Fleurdelis, Electroanalysis ( 1995 ) 476. ]231 J. Wang, B.M. Tian, Anal. Chim. Acta 270 ( 1992) 137.
[ 241 H. Braun, M. Metzger, Fresenius Z. Anal. Chem. 318 (1984) 321. [ 251 H.J. Diederich, S. Meyer, F. Scholz, Fresenius Z. Anal. Chem. 349 (1994) 670. [ 261 C. Hua, D. Jagner, L. Renman, Talanta 35 ( 1988) 597. [ 27 ] G.M. Greenway, G. Wolfbauer, Anal. Chim. Acta 312 (1995) 15. [ 28 ] C. Hua, D. Jagner, L. Renman, Talanta 35 ( 1988) 525. [ 291 J. Amel de1 Pozo, A. Costa Garcia, A.J. Miranda Ordieres, P. Tunon Blanco, Electroanalysis 4 (1992) 87. [ 301 J. Amel de1 Pozo, A. Costa Garcia, P. Tunon Blanco, Anal. Chim. Acta 289 (1994) 169. [ 311 M. Pedrero, B. Casado, F.J. ManueldeVillena, J.M. Pingarron, Fresenius Z. Anal. Chem. 349 (1994) 546. [ 321 W.H. Chart, H. Huang, Analyst 121 (1996) 1727.
Anastasios Economou is a postdoctoral research associate in the Depaltment of Chemistry, Laboratory of Analytical Chemistry University of Athens, Panepistimiopolis, Athens 157 71, Greece. Peter R. Fielden is a senior lecturer in the Department of instrumentation and Analytical Science, UMIST, PO Box 88, Manchester M60 IQD, UK.
book reviews Laser-enhanced
ionisation spectrometry
Laser-Enhanced lonisation Spectrometry, J.C. Travis and G.C. Turk, 1996, xi + 334 pages, ISBN 0-47157684-0.
This latest volume to the Chemical Analysis series of publications will provide an invaluable reference to accomplished researchers in the field of laser-enhanced ionisation (LEI) and to students alike, who may only be beginning their research in this fascinating subject. Indeed, this publication allows one to quickly become familiar with the basic principles of LEI within the first chapter, with real applications and instrumentation also being targeted at later stages. Optical
techniques such as LEI are being increasingly considered as viable alternatives to traditional methods of measurement within industry, and it is due to the emphasis that is placed on the practical issues involved in the technique that will make this book attractive to industrialists and academics alike. The publication takes you carefully through the fundamental issues relating to weakly ionised plasmas and the subsequent behaviour of the plasmas following excitation from a laser source which is tuned to a particular atomic transition. Issues such as ionisation efficiency, two-photon excitation and Stark broadening are considered, with experimental find-
ings and the developed theory being compared. The particular aspect which was most pleasing was the way in which sight was never lost of the practical issues surrounding the theory, and the logical approach in which the theory was built up from first principles. The authors fully acknowledge that the results produced by the various models do not correspond exactly to experiment. A most useful discussion is given which highlights the practical aspects of LEI which can lead to a deviation from the predicted behaviour. In fact, throughout the highly theoretical argument, the authors still manage to retain a practical bias, with the benefits of modern solid-state cw tuneable lasers highlighted as well as other potential improvements to the technique.
trends in analytical
XI
chemistry, vol. 16, no.5, 1997
account of the noise problems introduced by radio frequency interference common with this type of laser. Further practical issues such as electronic circuitry (filtering) and pre-amplification, noise characteristics and how to reduce their effects and limits of detection for the technique are also discussed. The authors conclude that this technique is amongst the most sensitive available for trace element analysis although there are still a number of problems since it is susceptible to many background interferences. For the future such a technique will be in direct competition with the ICP-MS system, already widely used in industry.
The basic instrumental configurations that have evolved over the years are also described. In general the discussion is presented in a clear and concise manner following logical steps through an LEI system from the atomisation stage to signal display. Different types of flame, e.g. air/acetylene, air/hydrogen etc., are discussed with relation to the issue of flame background ionisation. Mention is also made of other techniques using higher temperature plasmas where it is pointed out that LEI is more specific in its excitation. The discussion also describes the different laser pumping sources for the tuneable dye lasers preferred. Here the arguments for cw and pulsed lasers are clearly laid out centering on the excitation efficiency and how this can be optimised for differing laser irradiances, pulse lengths and repetition rates. The conclusion, that pumping via XeCl excimer lasers is preferred, is explained whilst taking
ANDREW
I. WHITEHOUSE
DI: A.I. Whitehouse is at the Optics and Photonics Group, BNFL UK Group, Sellafield, Seascale, Cumbria, CA20 IPG, UK.
-
Dietary fi bre analysis Dietary fibre analysis, by D.A.7: Southgate, RSC Food Analysis Monographs (Series editor t? S. Belton), 174 pages, 1995, ISBN 085404556-2 A good starting point when writing a book on analytical chemistry is to have the targeting compound or group of compounds well defined, and to use this basic information in an objective discussion of the performance of the various analytical methods. With dietary fibre it is not that simple as no general agreement has yet been reached about the very definition of dietary fibre and thus how it can be measured. The author consequently asks himself why write a practical handbook in an area where there is still so much dispute over even the most basic issues ? Fortunately the author convinced himself that there are justifiable reasons to write a book in his specialised area and can be satisfied with the outcome of the book which provides useful information for all analysts confronted with the difficult task of doing dietary fibre ana-
lysis. The book consists of eight chapters covering: the dietary fibre hypothesis, the chemistry of dietary fibre, analytical strategies, sampling and analytical quality assurance, the total dietary fibre method, the non-starch polysaccharide methods, other analytical methods for dietary fibre and its components and choice of analytical methods. In addition, the book contains an Appendix covering the preparation of in-house reference materials and a description of ANALOP, a system for identifying critical stages in an analytical protocol and quantifying their importance. The three first chapters give a good background and understanding of how the analytical techniques for measuring dietary fibre have evolved. Three major analytical approaches that have contributed to the development of current methods are discussed. The first group of methods derives from the analysis of the plant cell wall, the second group of methods derives from the analysis of the indigestible components in animal feeds and human foodstuffs, whilst the third
group of methods originates from the nutritional research environment. It is stressed that with no universally agreed definition an essential task of the analyst in designing analytical protocols is to make clear the purpose of the analyses. Although it may appear trivial the first and most crucial step in producing sound analytical data is the taking of a representative sample and its preparation. The author describes the various steps in the development of sampling protocols. He stresses that in the case of dietary fibre (and some other constituents) the requirement for a representative sample is slightly different depending on the purpose of the analysis, e.g. physiological studies, data bases, labelling, etc. The value of using certified and in-house reference materials to ensure the quality of the analytical results is further highlighted. The evolution of the two major methods for dietary fibre analysis the enzymatic-gravimetric total dietary fibre (TDF) method and the enzymatic-chemical non-starch polysaccharide (NSP) method are described in details in two chapters. These chapters are central and provide the reader with a good understanding of their different origins and backgrounds and how they have evolved in response to weaknesses identified in collaborative trials. Both methods have. undergone extensive collaborations, and details from these trials are discussed thoroughly. The author further assesses the methods by ANALOP to identify potential causes of imprecision and inaccuracy. It is striking that in spite of numerous improvements aimed at making the two types of methods more precise and robust, the methods are still not considered adequate for regulatory use because of their relatively poor precision and performance within and between laboratories. In addition to these two major groups of dietary fibre methods a separate chapter covers other methods that have been proposed for measurements of dietary fibre and its components. These include methods deriving from the chemistry of the plant cell wall, studies of the indigestibility components in foods and studies on the composition of food carbohydrates. Compared with the TDF and NSP