Signal , generally extraction

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 ... 

Wall M R and Neuhauser D 1995 Extraction, through filter-diagonalization, of general quantum eigenvalues or classical normal mode frequencies from a small number of residues or a short-time segment of a signal. 

Today, analytical chemistry has such a wide variety of methods and techniques at its disposal that the search for general fundamentals seems to be very difficult. But independent from the concrete chemical, physical and technical basis on which analytical methods work, all the methods do have one principle in common, namely the extraction of information from samples by the generation, processing, calibration, and evaluation of signals according to the logical steps of the analytical process. 

In similar work, Sturgeon et al. [125] compared direct furnace methods with extraction methods for cadmium in coastal seawater samples. They could measure cadmium down to 0.1 pg/1. They used 10 pg/1 ascorbic acid as a matrix modifier. Various organic matrix modifiers were studied by Guevremont [116] for this analysis. He found citric acid to be somewhat preferable to EDTA, aspartic acid, lactic acid, and histidine. The method of standard additions was required. The standard deviation was better than 0.01 pg/1 in a seawater sample containing 0.07 pg/1. Generally, he charred at 300 °C and atomised at 1500 °C. This method required compromise between char and atomisation temperatures, sensitivity, heating rates, and so on, but the analytical results seemed precise and accurate. Nitrate added as sodium nitrate delayed the cadmium peak and suppressed the cadmium signal. 

To define a feature extraction procedure it is necessary to consider that the output signal of a chemical sensor follows the variation of the concentration of gases at which it is exposed with a certain dynamics. The nontrivial handling of gas samples complicates the investigation of the dynamics of the sensor response. Generally, sensor response models based on the assumption of a very rapid concentration transition from two steady states results in exponential behaviour. 

HPTLC is a very fast and convenient assay to separate samples components and is often used in Organic Chemistry and in Synthetic approach. Unknown substances, after different display assay, were generally scraped off from the TLC/HPTLC plate, diluted into a tube and transferred into the MS system for structural elucidation and characterization. Now, a TLC-MS interface was developed by CAMAG, which can semi-automatically extract zones of interest and on-line direct them into any brand of a HPLC-MS system. The TLC-MS interface is connected by two fittings to any HPLC instrument coupled with mass spectrometer, without other system configuration adjustments or mass spectrometer modifications. By this way, the unknown substances can be directly extracted from a TLC/HPTLC plate, eluted and resolved by HPLC system and sensitive and selective mass spectrometric signals are obtained within a minute per substance zone [33],... 

In general, the signal acquisition process provides us with more data than needed. To extract relaxation parameters, we need a single value M(x) for each X setting, but we generally acquire a whole array of values. Clearly, some kind of data-reduction process must be implemented before the acquired signals can be used in the way we intend it to be. Like the NMR excitation techniques, the data reduction process can be exploited to enhance or suppress particular signal components. 

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