Analytical chemistry, definition

The units of concentration most frequently encountered in analytical chemistry are molarity, weight percent, volume percent, weight-to-volume percent, parts per million, and parts per billion. By recognizing the general definition of concentration given in equation 2.1, it is easy to convert between concentration units. 

It is becoming more and more desirable for the analytical chemist to move away from the laboratory and iato the field via ia-field instmments and remote, poiat of use, measurements. As a result, process analytical chemistry has undergone an offensive thmst ia regard to problem solviag capabihty (77—79). In situ analysis enables the study of key process parameters for the purpose of definition and subsequent optimization. On-line analysis capabihty has already been extended to gc, Ic, ms, and ftir techniques as well as to icp-emission spectroscopy, flow iajection analysis, and near iafrared spectrophotometry (80). 

Control of metalloid content in natural objects, foodstuff and pharmaceuticals is an important task for modern analytical chemistry. Determination of elements such as Arsenic is necessary for evaluation of object toxicity, since their content in environment may exceed MCL (maximum contaminant level), posing hazard to human health. Elements such as Selenium in definite doses are healthy, but in greater quantities they produce toxic effect. 

This definition outlines in very broad terms the scope of analytical chemistry. When a completely unknown sample is presented to an analyst, the first requirement is usually to ascertain what substances are present in it. This fundamental problem may sometimes be encountered in the modified form of deciding what impurities are present in a given sample, or perhaps of confirming that certain specified impurities are absent. The solution of such problems lies within the province of qualitative analysis and is outside the scope of the present volume. 

However, now and then analytical chemists feel uneasy with such kinds of definitions which do not reflect completely the identity and independence of analytical chemistry. Chemists of other branches (inorganic, organic, and physical chemists) as well as physicists and bioscientists also obtain information on inanimate or living matter using and developing high-performance analytical instruments just as analytical chemists do. 

Consequently, there exists a wide range of diverse definitions. One of the most appropriate is that of Reilley [1965] Analytical chemistry is what analytical chemists do which is, however, not really helpful. 

The first definition that is focused directly on the role of analytical signals was given by Pungor who characterizes analytical chemistry as a science of signal production and interpretation (Veress et al. [1987], Lewenstam and Zytkow [1987]). Zolotov [1984] characterized chemical, physicochemical and physical methods of analytical chemistry as follows All of them, however, have the same feature it is the dependence of signal on analyte... 

To overcome the unsatisfactory situation in the understanding the meaning of analytical chemistry at the end of the last century, an international competition was organized in 1992 by noted European analytical chemists and the Fresenius Journal of Analytical Chemistry to characterize analytical chemistry as an autonomous field of science by a topical and proper definition. The title of this competition was Analytical Chemistry - today s definition and interpretation and 11 out of 21 contributions were published in Fresenius J Anal Chem (Fresenius and Malissa [1992] Cammann [1992] Valcarcel [1992] Zuckerman [1992] Zhou Nan [1992] Koch [1992] Perez-Bustamante [1992] Ortner [1992] Danzer [1992] Green [1992] Stulik and Zyka [1992] Kuznetsov [1992]). 

All these definitions express essential aspects of analytical chemistry and the analytical work. Some others - with originality - could be added, such as that from Murray [1991] who characterized analytical chemistry briefly and aptly as the science of chemical measurements . 

Cammann, K (1992) Analytical chemistry - today s definition and interpretation. Frese-nius J Anal Chem 343 812... 

WPAC (1993) Edinburgh definition of analytical chemistry see Kellner, R (1994)... 

The technical terms homogeneity and inhomogeneity defined in analytical chemistry must be distinguished from the physicochemical concept of homogeneity and heterogeneity (Danzer and Ehrlich [1984]). Whereas the thermodynamical definition refers to morphology and takes one-phase-or multi-phase states of matter as the criterion, the analytical-chemical definition is based on the concentration function... 

Signals used in analytical chemistry have a definite origin from particular species or given structural relationships between constituents of samples. The relation of the sample domain and the signals domain, i.e. the coding and decoding process as represented in Fig. 2.12, must be as unambiguous as possible. 

In clinical chemistry and medical diagnostics the true positive rate is called sensitivity rate and the true negative rate specificity rate (O Rangers and Condon [2000]) without any relation to the general definition of the terms sensitivity and specificity and their use in analytical chemistry (see Sects. 7.2 and 7.3). 

Danzer K (2001) Selectivity and specificity in analytical chemistry. General considerations and attempt of a definition and quantification. Fresenius J Anal Chem 369 397... 

Signal-to-noise ratio characterizes recorded signals and signal functions with regard of their quality, i.e., their precision. Unfortunately, the signal-to-noise is not uniformly used in analytical chemistry. In addition to the definitions given in Eqs. (7.1) and (7.2), there exist another one, related to the peak-to-peak noise Npp ... 

It is difficult to comprehend why this measure has not been applied in analytical chemistry. Instead of this, in the last decades the signal-to-noise ratio has increasingly been used. Signal-to-noise ratio, see Eq. (7.1), is the measure that corresponds to r in the signal domain. In principle, quantities like S/N (Eq. (7.1)) and / (Eq. (7.7)) could represent measures of precision, but they have an unfavourable range of definition, namely range[r = range[S/N] = 0... oo. 

The limits CV, LD, and LQ are widely applied in analytical chemistry but, unfortunately, not in a standardized manner. Various concepts are in use as well as different terms, symbols, definitions and meanings. Overviews are given and consequences are shown among others by Currie [1995, 1997] Long and Winefordner [1983] Fleming et al. [1997a] Geiss and Einax [2001] Ehrlich and Danzer [2006]. 

Hulanicki A., Glab S., Ingman F., Chemical sensors definitions and classification. Commission on General Aspects of Analytical Chemistry, Pure Appl. Chem. 1991 63 1247. 

Advanced mathematical and statistical techniques used in analytical chemistry are often referred to under the umbrella term of chemometrics. This is a loose definition, and chemometrics are not readily distinguished from the more rudimentary techniques discussed in the earlier parts of this chapter, except in terms of sophistication. The techniques are applied to the development and assessment of analytical methods as well as to the assessment and interpretation of results. Once the province of the mathematician, the computational powers of the personal computer now make such techniques routinely accessible to analysts. Hence, although it would be inappropriate to consider the detail of the methods in a book at this level, it is nevertheless important to introduce some of the salient features to give an indication of their value. Two important applications in analytical chemistry are in method optimization and pattern recognition of results. 

The following list of definitions, though by no means exhaustive, will help both in the study and practice of analytical chemistry. 

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