Chromatography qualitative peak information

In chromatography the quantitative or qualitative information has to be extracted from the peak-shaped signal, generally superimposed on a background contaminated with noi%. Many, mostly semi-empirical, methods have been developed for relevant information extraction and for reduction of the influence of noise. Both for this purpose and for a quantification of the random error it is necessary to characterize the noise, applying theory, random time functions and stochastic processes. Four main types of statistical functions are used to describe the tosic properties of random data ... 

As a qualitative tool, gas chromatography has been limited to retention data and a variety of ancillary techniques. Despite the limitation, retention data are widely used, and various tabulations of such information are available (2). Because mass chromatography provides both molecular weight and retention time for each peak, the technique represents a powerful means of identifying compounds as is illustrated in Figure 3 and Table I. 

In theory, GC retention times should be useful for identifying components in mixtures. In fact, however, the applicability of such data is limited by the number of variables that must be controlled to obtain reproducible results. Nevertheless, gas chromatography provides an excellent means of confirming the presence or absence of a suspected compound in a mixture, provided that an authentic sample of the substance is available. No new peaks in the chromatogram of the mixture should appear on addition of the known compound, and enhancement of an exi.st-ing peak should be obseiwed. The evidence is particularly convincing if the effect can be duplicated on different columns and at different temperatures. On the other hand, because a chromatogram provides but a single piece of information about each species in a mixture (the retention time), the application of the technique to the qualitative analysis of complex samples of unknown composition is limited. 

Ion chromatography can be used as a qualitative or quantitative technique. Qualitative information allows a substance to be identified on the basis of retention time comparisons between a standard and the sample ion. When used quantitatively, the IC can employ external or internal standards to generate a standard curve. Then, the peak area of the sample peak on the chromatogram can be used to obtain a concentration. 

As with chromatography, the position of the peak in IMS provides qualitative information. The location of the ion swarm as it exits a drift region is dependent on the type of instrumentation used For drift tube instruments, it is the arrival time of the ion swarm at the Faraday plate or mass spectrometer orifice for DMS, it is the compensation voltage required to create a stable path through the instrument, and for aspiration-type instruments, it is the location of the Faraday plates as a function of the strength of the electric field. All of these qualitative measurements can be related to the mobility of the ion swarm, although in some cases this relation is complex and not well understood. Nevertheless, the relationships of K, K, and fl to ion mobility spectra have been described elsewhere in this book and serve as the qualitative basis of IMS. Until the fundamental relation of ion-molecule interactions can be understood sufficiently to model ion behavior in IMS instruments, IMS standards will serve to calibrate the various IMS platforms. 

A chromatogram provides information on the complexity (number of peaks), identity (retention time), and quantity (peak area or height) of the components in a mixture. This information can be considered suspect if the quality of separation is not optimal. Capillary columns have greatly enhanced the u.se of gas chromatography as a qualitative and quantitative tool. 

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