Generalized-peak-shape method

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 ... 

Gas chromatography is a useful adjunct to the schemes previously described. The fractions remaining from Scheme 2 can be examined directly by gas chromatography or, alternatively, the miCTO-extraction method, described below, can be used. The most generally useful system for screening is one using a dimethylsilicone stationary phase such as SE-30, OV-1, or OV-101, Volatile amines elute with a better peak shape on alkaline columns such as Apiezon L coated with potassiiun hy(hoxide. 

More precise information about the details of such anomalous radical eliminations resulted from the detailed investigation of labelled compounds of the general structure 45 51. Here the combined application of different methods e.g., appearance potential measurements, peak shape analysis, CA studies, kinetic energy release) established that the cleavage of a heteroatom-carbon bond can take place via two fundamentally different mechanisms ... 

In the analytical procedure, an accurately measured aliquot of the product is diluted Avith a diluent (normally the mobile phase) and the resulting sample solution is injected into the HPLC. Because the majority of injectable pharmaceuticals are clear solutions, typically a simple dilution step is all that is needed for sample preparation. However, if the parenteral product is an emulsion or a suspension, appropriate steps must be taken to dissolve the product to achieve a clear solution (ultrasonication, filtration, etc.). For the assay procedure, the sample concentration chosen should be such that the peak areas obtained from multiple injections from the same sample are reproducible with minimum variance (<2% relative standard deviation). Peak shape and retention time also play important roles in the precision of the assay. A tailing factor less than 1.5 and a capacity factor less than 10 for the active peak are generally required for a good analytical method. A reference standard solution having the same concentration and using the same diluent as the sample solution is prepared. 

Analytical applications of electrochemistry, where the objectives are well defined, have fared better. There is a long list of papers going back twenty years on the applications of computers and then microprocessors. Reviews of this subject appear in the Fundamental Reviews sction of Analytical Chemistry (see refs. 8 and 9). In general, the aim in electroanalytical methods is to avoid interfering effects, such as the ohmic loss and the double layer capacity charging, and to use the Faradaic response peak current-potential curve as an analytical tool. Identification of the electroactive species is achieved by the position of the response peak on the potential axis and "pattern recognition , and quantitative analysis by peak shape and height. A recent development is squarewave voltammetry [10]. 

The general use of series (or parallel) coupled detectors has been to record different channels of independent information as a method of qualitative identification [391,392]. The use of detector ratios for compound identification has declined with the development of low cost mass spectrometers that allow the use of more reliable identification methods. There are also practical problems related to long term stability of response ratios and their system dependence. Although rarely addressed in the literature, the chromatograms recorded with series coupled detectors often show greater peak shape deterioration than predicted from consideration of the additional coupled detector volume. 

Nonsuppressed IC methods for natural water samples are generally 1-2 orders of magnitude less sensitive for common inorganic anions than suppressed conductivity methods, but still find useful application for the determination of higher-concentration matrix anions, such as chloride and sulfate. Typical eluents used include p-hydroxybenzoic acid or phthalic acid, often used with small amounts of organic solvent to improve peak shapes. Such eluents can also be employed for indirect UV detection, although again sensitivity is somewhat less than for direct UV detection. 

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