Peak recognition

J.K. Strasters, H.A.H. Billiet, L. de Galan.B.G.M. VandeginsteandG. Kateman, Evaluation of peak-recognition techniques in liquid chromatography with photodiode array detection. J. Chromatog., 385 (1987) 181-200. 

Chart speed or x-axis scale Data system Sets the x-axis scale for the plotted chromatogram Changes appearance of chromatogram Does not change peak recognition, retention time, area or width Does not affect the raw data... 

Most of the detectors permit peak recognition but provide no structural information, which can be particularly important for identification of unknown compounds. From this point of view, the spectro-metric detectors, specifically mass spectrometer and photodiode array detectors, add a third dimension to the multidimensional system and give additional information useful in components identification. 

A. F. Fell, H. P. Scott, R. Gill, and A. C. Moffat, Novel techniques for peak recognition and deconvolution by computer aided photodiode array detection in high-performance liquid chromatography, J. Chromatogr., 282 123 (1983). 

Issaq and McNitt [585] published a computer program for peak recognition on the basis of peak areas. They investigated the reproducibility of the area of some well-separated peaks for three solutes (anthraquinone, methyl anthraquinone and ethyl anthraquinone) in the 10 solvents used for their optimization procedure. The solvents included binary, ternary and quaternary mixtures of water with methanol, acetonitrile and THF. The areas were found to be reproducible within about 2 percent. The wavelength used for the UV detector in this study was not reported. 

The problem of peak recognition may be seen as a simplified version of the problem of peak identification. The spectra found during the elution of a chromatogram can be subjected to automated retrieval systems [589]. In this case the peak may be tentatively identified by comparing its spectrum to a (potentially large) number of reference spectra,... 

In general retrieval systems, additional information such as retention data may be required for a conclusive peak recognition using UV spectra [590]. For obvious reasons, however, retention data cannot be used as an aid for peak recognition for optimization purposes. Related solutes, such as isomers and homologues, may show similar spectra, which are hard to differentiate. In case of doubt, one may have to refer to peak areas for additional information. Again (see section 4.6.1), this requires very good resolution of the individual peaks. 

A remaining problem for all spectrometric peak recognition methods is the reproducibility of the spectra recorded under different chromatographic conditions. For example, if the differences between the UV spectra for a given solute induced by variations in the mobile phase in RPLC are larger than the differences between the UV spectra of different solutes recorded under identical conditions, then clearly the application of multichannel UV detection, with or without the use of PCA techniques, will be of limited use. 

Simultaneous interpretive methods are a good way to locate the global optimum in a small number of experiments, but the requirements are shifted towards good models, computers, and peak recognition methods. 

The method for this example was limited to positive-ion mode and relied on peak recognition and processing from being > in the diode-array trace or being within 4... 

An automatic peak search is actually the simplest (one-dimensional) case in the more general two- or three-dimensional image recognition problem. Image recognition is easily done by a human eye and a brain but is hard to formalize when random errors are present and, therefore, difficult to automate. Many different approaches and methods have been developed two of them are most often used in peak recognition and will be discussed here. These are the second derivative method and the profile scaling technique. 

After peak recognition both flanks are searched for the half height (above background, possibly by interpolation) and the difference of the corresponding x-values is taken as full width at half maximum of this peak (FWHM, short half-width). This difference should surpass a certain threshold (e.g. 0.06° in 20) to accept a found elevation above background as a true reflection. Thus, one has a further possibility at this point to eliminate possible outliers because they cause much narrower peaks than real reflections. 

H. Baadenhuijsen and T. Zelders, The Use of a Microcomputer System for Peak Recognition, Data Processing and Representation in Continuous Flow Analysis. J. Autom. Chem., 5 (1983) 18. 

F. Ehrentreich, S.G. Nikolov, M. Wolkenstein and FI. Hutter. The Wavelet Transform A New Preprocessing Method for Peak Recognition of Infrared... 

The method giving the closest approximation of visual-peak recognition is the curve-fit-ting method. But this requires a clearly known profile function. 

Figure 30. Peak recognition and characterization (Courtesy of Metrohm).

Mass spectrometric detector selectivity provides imequivocal identification of target compoimds. By targeting the MW and by using specific software, fully automated peak recognition is possible. Compoimds need to be efficiently ionized for their detection. The single-quadmpole Waters ZQ is equipped with the two commonly available ionization sources electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). As most of the compounds to be examined were basic, electrospray with positive ionization was our method of choice. The selection of E SI was supported by previous experience gained over the last three years in our laboratory about 96% of the identified compounds, corresponding to more than 9,000 different molecules, were successfully analyzed with the ESI interface. 

In some cases, the implicit learning axiom is not fulfilled. In these cases, mistakes either of first peak recognition or of median computation can be found. In... 

Data acquisition and processing (peak recognition and integration)... 

DATA ACQUISITION AND PROCESSING (PEAK RECOGNITION AND INTEGRATION)... 

Peak Recognition with a Single Channel Signal... 

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