Anal Bioanal Chem (2004) 380: 368–369 DOI 10.1007/s00216-004-2792-x

E D I T ORI AL

Ju¨rgen W. Einax

Chemometrics in analytical chemistry

Published online: 3 September 2004 Ó Springer-Verlag 2004

Analytical chemistry today is a fast-growing and developing science. Strongly connected to analytical chemistry, receiving impetus from it, and providing impetus back, chemometrics is also developing in a remarkable way. Many analytical chemists apply chemometric principles and methods in their daily work, partly intentionally and partly due to the software used in their equipment. But some analytical chemists are also somewhat critical of chemometrics since it can seem to be complicated, mysterious, and, therefore, potentially suspect. This special issue of ‘‘Analytical and Bioanalytical Chemistry’’ intends to reduce this distance between analytical chemists and chemometrics, and to encourage them to use it in their daily work. The articles published will help to disseminate chemometric knowledge among the analytical chemists community and therefore will help to close the gap between chemometricians and practitioners in the field of analytical chemistry. The first questions we should ask about chemometrics are: what is it? What are its roots, and which fields make use of it? Chemometrics is—according to the actual definition of the International Chemometrics Society—the chemical discipline that uses mathematics, statistics, and formal logic – To design or select optimum experimental and measurement procedures – To provide maximum relevant chemical information by analyzing chemical data – To obtain knowledge about chemical systems Statistical and mathematical methods were first applied in psychology, biology, and agriculture at the beginning of the last century. Chemometrics, however, is a rel-

J. W. Einax Institut fu¨r Anorganische und Analytische Chemie, Lehrbereich Umweltanalytik, Friedrich-Schiller-Universtita¨t Jena, Lessingstr. 8, 07743 Jena, Germany E-mail: [email protected]

atively young science that was born at the end of the 1960s and became an independent working field in the 1970s. The name ‘‘chemometrics’’ was first coined by the Swedish scientist Svante Wold in the early 1970s. His cooperation with the American analytical chemist Bruce R. Kowalski, who at the time was working on pattern recognition methods in chemistry, resulted in the foundation of the International Chemometrics Society in 1974. The first German working party on chemometrics was founded in 1984. Around this time chemometric working groups were also established in many other countries. The rapid development of chemometrics in the 1980s also found its expression in the publication of two journals specializing in chemometrics: ‘‘Chemometrics and Intelligent Laboratory Systems’’ (1986) and the ‘‘Journal of Chemometrics’’ (1987). Other journals that have analytical chemistry as their main topic, like ‘‘Fresenius’ Journal of Analytical Chemistry’’, ‘‘Analytical and Bioanalytical Chemistry’’, and ‘‘Analytica Chimica Acta’’ also published more and more chemometric papers. In the 1980s the first monographs on chemometrics were published, and networks teaching chemometrics were established. The driving forces for the development of chemometrics were on the one hand the fast development of powerful computers and convenient and easy-to-use software packages, and on the other hand, analytical chemists that were using more efficient and productive analytical equipment were (and still are) being faced with increasingly complex and complicated tasks. In particular, the flood of data ‘‘produced’’ by modern multielement and multicomponent analytical apparatus requires the application of chemometric methods in order to be able to pick the essential influencing factors from many possible influences, to quantify their relationships, and to extract the latent information from immense amounts of data. Important working fields for today’s chemometrics are:

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Descriptive statistics Planning and evaluation of sampling Experimental design and optimization Signal detection and univariate signal processing Calibration Multivariate signal processing Multivariate data analysis Geostatistical methods Time series analysis Soft modeling Laboratory information and management systems Library search and expert systems Analytical quality assurance Process analysis and optimization

These various topics demonstrate that chemometrics must be interdisciplinary to a great extent. Chemometrics has many origins within analytical chemistry, but it is not exclusive to this domain. Other applied scientists (environmental, clinical and forensic, food, industrial, biological, theoretical and physical, organic chemistry) need chemometrics to plan their experiments and to interpret their data. Scientists from engineering and computer sciences as well as applied and pure statistics and mathematics also use it. The actual development of chemometrics is characterized by activities to preserve the underlying reality of data as much as possible during all statistical and mathematical operations. The following main tendencies are detectable: – Optimum treatment of data sets in a bad condition, not normally distributed, with missing values, and influenced by outliers – Evaluation of high-dimensional multiblock-multiway data sets, often combined with feature selection – Introduction of new algorithms (projection methods) for the visualization of multi-dimensional data and their interactions – New methods of signal processing The application of neural networks for the description of complex and often non-linear relationships is—with increasing weight—growing. A further trend is

arising from the capabilities of modern multielement and multicomponent analysis: the selection of features describing the problem under investigation by means of evolutionary, mostly genetic, algorithms. Multivariate modeling with common and modern methods is still an important field of actual chemometrics. Partial-leastsquares regression continues to be applied for the treatment of multiway problems. Wavelet transformation—often used in spectroscopy for signal processing and resolution—is a further topic of chemometrics today. Current developments are characterized more by applications of chemometrics than by fundamental work. In addition to classical problems of analytical chemistry, like the optimization of methods, interdisciplinary works are gaining much interest. The investigation of the environment, of food and pharmaceuticals, and chemometric modeling of technological processes and process analytical chemistry must be mentioned here. A further important topic is the application of chemometrics to analytical quality assurance. The special issue ‘‘Chemometrics in analytical chemistry’’ in ‘‘Analytical and Bioanalytical Chemistry’’ presents state-of-the-art papers from internationally renowned experts working in chemometrics. I hope it will stimulate the reader into learning more about chemometrics and about how to apply chemometric methods in their own fields. Ju¨rgen W. Einax is Professor of

Analytical Chemistry at the Friedrich Schiller University of Jena, and Head of the Department of Environmental Analysis. His main areas of research include not only trace analytical problems in the environment, but also the application of chemometrics to environmental research. He is the Chairman of the Working Party for Chemometrics and Laboratory Data Processing of the Division of Analytical Chemistry of the German Chemical Society.