Types and Properties of Analytical Signals

For the analytical representation the signals have to be transformed from time functions into conventional measuring functions. These are characterized by analytical quantities on abscissa and ordinate axes where the values of them may be relativized in some cases (e.g. MS). Such a transformation of quantities is mostly carried out on the basis of instrument-internal adjustment and calibration. 

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. 

This has led to such cases in the history of chemistry that spectroscopic signals have been unidentified till newly discovered elements was found (e.g. rubidium, caesium, indium, helium, rhenium) or new species (highly ionized atoms, e.g. in northern lights [aura borealis], luminous phenomena in cosmic space and sun aura, such as nebulium , coronium , geocoronium , asterium , which was characterized at first to be new elements see Bowen [1927] Grotrian [1928] Rabinowitsch [1928]). 

Signal functions may have a very different character even in case of one and the same analytical method as Fig. 3.4 shows. 

In general, signal functions will be obtained in analogous form and consist of a large number of arranged measured points which form a data vector. There are three types of signal functions, which contain  

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Two somewhat different types of null hypotheses are tested, one during the development and validation of an analytical method and the other each time the method is used for one purpose or another. They are stated here in general form but they can be made suitably specific for experimentation and testing after review and specification of the physical, chemical and biochemical properties of the analyte, the matrix, and any probable interfering substances likely to be in the same matrix. Further, the null hypotheses of analytical chemistry are cast and tested in terms of electronic signal to noise ratios because modern analytical chemistry is overwhelmingly dependent on electronic instrument responses which are characterized by noise. 

In analytical chemical terms this means all steps of the analytical procedure should be performed and recorded in such a way that all essential information is available and no wrong information is introduced. In other words, the results of the determination and not only the final measurement should be linked through an unbroken chain of comparisons. This link must be demonstrated. Depending on the type of analytical method applied and the property of interest to be determined, various steps may be necessary to demonstrate the link between the end signal recorded from the detector and the reference to which it is linked. 

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