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A must-read for GC users
his fourth edition covers all of the basic aspects of GC, including theory, columns (packed and capillary), detectors, inlets, qualitative and quantitative analyses, and GC/MS. Surprisingly, many of the chapters are covered in a level of detail that is not available in most current books. For example, the chapter on theory comprehensively illustrates frontal, displacement, and elution chromatography; isotherms; linear and nonlinear chromatography; and plate theory. The chapter also includes
the discrete flow model and the random walk approach for deriving the classical van Deemter equation (rate theory), a must for teachers and students of separation science. My only disappointment was the absence of the Golay equation for capillary columns in this chapter. However, it is adequately covered in the chapter on columns. Another example of in-depth coverage by the author is the chapter on detectors. Common detectors are thoroughly discussed, and other topics are also detailed: helium ionization, chemiluminescence, atomic emission, Hall electrolytic conductivity, and ultrasound detectors. The reader will be delighted to know that, as in other chapters, excellent references follow each discussed topic. The chapter on columns discusses both packed and capillary columns; this is probably the only current book that covers packed columns with such a high level of detail. The chapter covers solid supports and adsorbents used in gas–solid chromatography, and capillary columns are also discussed. A useful table (3.6) is the U.S. Pharmacopeia designation for popular supports and adsorbents. Details about fused silica tubing, aluminum-clad fused silica (for high-temperature GC), silanol deactivation, liquid phases, coat-
ing procedures, test mixtures, megabore columns, and important column parameters are all included. In addition to the fundamentals, new chapters on fast GC, GC/MS, sample prep, optimization and computer assistance, and QA/QC validation of methods are included. These cover all of the current hot topics in GC with the exception of multidimensional GC, which merits less than two pages in the GC/MS chapter. More than 400 pages are devoted to applications and sample prep, and many useful chromatograms and references are included. One author could not possibly write such a varied text, so the editors chose 20 experts to write in their areas of expertise. The authors have different writing styles, but good editing has overcome this problem. All authors use the same terminology, thus ensuring minimal overlap of material. Despite the book’s huge size (1045 pages) and hefty price ($150), it is easy to read. For students and professors of GC, this edition is a must-have. It is comprehensive and contains many special topics, including all the current references needed to continue your study.
Catching the chemometrics wave
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metrics. Challenges that chemists must tackle when analyzing their data are enumerated through a few examples. Jargon used in chemometrics is introduced in this chapter, but the authors do not provide explicit definitions for these terms; this deficit detracts from the presentation. The authors conclude the chapter by presenting a brief introduction to wavelets and commercial software packages for chemometrics. Chapter 2 focuses on signal processing techniques commonly used for analytical data represented as 1-D vectors, for example, spectra and chromatograms. Moving-average and Savitsky–Golay filtering techniques for smoothing data are discussed as well as the MATLAB codes for these two techniques. The use of the Fourier transform for denoising and data compression is also presented. The chap-
Modern Practice of Gas Chromatography Edited by Robert L. Grob and Eugene F. Barry Wiley Interscience, 2004, 1045 pp, $150, www.wiley.com
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Chemometrics: From Basics to Wavelet Transform Foo-tim Chau, Yi-zeng Liang, Junbin Gao, and Xue-guang Shao Wiley Interscience, 2004, 316 pp, $99.95, www.wiley.com © 2005 AMERICAN CHEMICAL SOCIETY
hemometrics is a subfield of analytical chemistry that uses mathematical, statistical, and other methods of formal logic to extract information from chemical data. Too much data, which is a direct result of the dramatic increase in the number and sophistication of chemical instruments, has triggered interest in the development of new data analysis techniques to optimize instrument performance, for example, to resolve overlapping peaks and improve instrumental calibration. This text, volume 164 in the Chemical Analysis series, discusses wavelets, a recent development in mathematics. Wavelets have been used to smooth data, remove background, eliminate sloping baselines, and enhance resolution. The text is divided into five chapters. In Chapter 1, the authors provide the reader with a brief history of chemo-
Reviewed by Harold McNair, Virginia Polytechnic Institute
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books and software
ter concludes with a discussion of principal component analysis (PCA). These techniques and the ideas they embody provide the reader with the necessary background to understand how one could use wavelets to improve the quality of information obtained from data. Chapter 3 focuses on signal processing techniques used in multivariate curve resolution (MCR) for data obtained from so-called hyphenated methods. In this case, a sample is represented as a matrix of measurements; the authors explain the advantages of using PCA to analyze this type of data. Preprocessing techniques for two-way data are also treated in the chapter. However, some of the methods discussed by the authors—those for MCR methods and those for two-way data—do not adequately reflect the present state of the art. The chapter concludes with a survey of several methods used in peak deconvolution: evolving factor analysis, window factor analysis, local rank analysis, and heuristic evolving latent projections. Chapter 4 focuses on the wavelet transform and the wavelet packet transform. Because of their localization properties, wavelets are often preferred over the Fourier transform in applications involving data compression, resolution, and signal enhancement of data. In this chapter, the authors first discuss the idea of decomposing a function or vector into templates, that is, wavelets derived from a mother wavelet through scaling and translates. Next, the Haar wavelet and its properties are introduced. A summary of Mallat’s multiresolution signal decomposition algorithm is presented, and a technique used to construct wavelet functions is shown. Wavelet functions that are examined include Meyer wavelets, B-spline wavelets, and Daubechies wavelets. The authors explain the fast wavelet transform, which is used to express a signal in terms of the corresponding wavelet functions, and the inverse wavelet transform, which is used to reconstruct the signal from the remaining wavelet coefficients. They end the chapter with discussions of the packet wavelet and the 2-D wavelet transform. In Chapter 5, the authors focus on applications of the wavelet transform to analytical chemistry, with examples illus78 A
trating data compression, denoising and smoothing, baseline/background removal, and resolution enhancement. In my opinion, this is the best chapter in the text because the authors use examples to convey to the reader the properties and unique attributes of wavelets. The authors provide the server location for MATLAB codes for the examples presented in this chapter and list a Stanford University website that contains a toolbox for developing wavelet programs. The chapter concludes with a survey of the analytical literature. The authors have made an effort to be straightforward in the presentation of the material, but there are mistakes that detract from the text. Hyphenated instrumentation is not a recent advance, as stated on page 1; GC/MS has been in existence for >30 years. On page 4, the authors state that chromatogram 1b is preferred from an information analysis viewpoint. Unfortunately, the text references unpublished work, which is of no help to the reader. It would have been better for the authors to simply state that chromatogram 1b is preferred because it represents a compromise between information about the mixture (i.e., numbers of peaks) and noise (sloping baseline). On page 9, the authors describe Kvalheim’s concept of white, black, and gray systems, which he has used to describe problems in MCR. In view of recent developments in MCR, these designations are no longer important, since it is now possible to identify components present in so-called black systems. On page 23, the standard deviation, not the variance, is only 1/n0.5 of the mean, not of the original measurement variable. On page 24, the data set used to demonstrate the performance of the moving-window average smoothing method and the Savitsky–Golay filter yielded the same results as shown in Figures 2.1 and 2.2. Therefore, the claim made by the authors that Savitsky–Golay is better than moving-window average smoothing cannot be substantiated by the example they provide. The discussion on page 65 about computing the scores and loadings from PCA is not correct. If each sample is represented as a row vector, than Equation 2.74 is incorrect and each element of ma-
A N A LY T I C A L C H E M I S T R Y / F E B R U A R Y 1 , 2 0 0 5
trix U should be multiplied by its corresponding eigenvalue. If each sample in the data matrix is represented as a column vector, then Equation 2.74 is correct, but ui and vi should be the loadings and the scores, not the scores and the loadings. The statement on page 70 that noise in spectrochromatographic data is usually heteroscedastic was true ~10 years ago but is not true today because of improvements in diode array detector technology. Despite these mistakes, my overall impression of the text is favorable. The authors have done a decent job of explaining wavelets. However, the material in the chapters preceding wavelets should be revised in future editions to better reflect present trends in the literature and to facilitate the logical flow of ideas crucial to understanding wavelets. In conclusion, I recommend this book to chemists who are interested in using wavelets in their research and to faculty who would like to teach graduate students about signal processing in a graduate course on spectroscopy. Reviewed by Barry K. Lavine, Oklahoma State University
Books Received b b A Practical Guide to Understanding the NMR of Polymers Peter A. Mirau John Wiley & Sons, 2005, 418 pp, $94.95, www.wiley.com This book provides an introduction to the theory and practical applications of NMR in polymer science. Topics include chemical shifts, spin–spin coupling, multidimensional and solid-state NMR, and solution characterization of polymers. The text provides numerous examples and references. The book gives students and researchers in polymer and analytical chemistry a comprehensive introduction to NMR. Students and researchers in polymer and analytical chemistry will find this book a useful resource.
