Library search aids

Provided that the compounds analysed in positive mode are not known, the selected and fragmented compound ions (cf. Fig. 2.5.7(b)—(d)) after computer aided product ion library search were described as AE (Fig. 2.5.7(b) and (c)) and polyglycol amines... 

In the past, PTRC screening was mainly based on gas chromatography-mass spectrometry (GC-MS) [116]. The choice of GC-MS was based on a number of good reasons (separation power of GC, selectivity of detection offered by MS, inherent simplicity of information contained in a mass spectrum, availability of a well established and standardized ionization technique, electron ionization, which allowed the construction of large databases of reference mass spectra, fast and reliable computer aided identification based on library search) that largely counterbalanced the pitfalls of GC separation, i.e., the need to isolate analytes from the aqueous substrate and to derivatize polar compounds [117]. 

Self-collected or purchased IR spectra libraries " are very useful for the identification of unknown substances. With computer-aided library searches acorrespondence... 

Library Search Routines To aid in the identification of hydrocarbons, computer programs are being developed for comparing unknown spectra to libraries of known compounds. As an example, a sample of 2-hexadecanol was compared to a library of over 100 compounds. The library search identified 2-hexadecanol as the... 

COMPUTER-AIDED SPECTROSCOPIC STRUCTURE ANALYSIS OF ORGANIC MOLECULES USING LIBRARY SEARCH AND ARTIFICIAL INTELLIGENCE... 

Factors 1 and 2 are correlated usually, a decrease/increase of the reproducibility of the fingerprint data will cause a decrease/increase of the specificity of that data. Factors 2 and 4 are also correlated. As a matter of fact, the reproducibility of the data involved in a search system is a crucial element of the design of the similarity index. Especially the interlaboratory reproducibility plays an important role, whenever multisource databases are being used. This reproducibility is determined by differences in samples, instruments, experimental conditions, performance of analysts and operators, introduction of coding errors, etc. As a consequence, a major factor determining the usefiilness of computer-aided library search systems is the extent to which the reproducibility of the relevant data is accounted for in the design of the similarity measure. 

Boessenkool, H. J., Cleij, P., van t Klooster, H. A., Goewie, C. E., van den Broek, H. H. Computer-aided Library Search of Combined LC Retention and Diode-array UV Spectral Data. Mikrochim. Acta 1987, 2, 75-92. 

Two separate teams, those of Wolfgang Bremser and Henk van t Klooster, were chosen to cover the subject of spectral databases, computer-aided library search systems and expert systems for structure analysis. 

All the above procedure may assume less significance if computer-aided library searching is available. The library may not contain an entry for the sample under examination, but will always provide a best-match spectrum. Close scrutiny of the goodness of fit of the library and acquired data is therefore essential if the possibility of an erroneous match is to be avoided. 

Template searches in THREADER were performed with the primary sequence and the primary sequence with the predicted secondary structure as determined by PSI-PRED. The results of a THREADER template search aided by the predicted secondary structure information can then be analyzed with the Threading Expert. The top five templates based on Z-Score (Primary and Secondary) and overall Score (Threading Expert) are presented. The original THREADER library was used. 

A manual library search may take a lot of time. Convenient aids are available, however (3, 4, 24, 29), and with experience it may be preferable sometimes to use time-consuming time-sharing search (3, 49). 

The interpretive NMR library search in SESAMl (systematic elucidation of structure applying machine intelligence), INFERCNMR, does not utilize a set of predefined substructures derived from a database. Its function is to retrieve any substructure present in the reference compounds of the library that is predicted to model a substructure of the unknown. No restrictions are placed on the size of or arrangement of atoms in the substructure. INFERCNMR can also serve as a stand-alone interpretation aid for the chemist/spectroscopist. 

Woodruff and co-workers introduced the expert system PAIRS [67], a program that is able to analyze IR spectra in the same manner as a spectroscopist would. Chalmers and co-workers [68] used an approach for automated interpretation of Fourier Transform Raman spectra of complex polymers. Andreev and Argirov developed the expert system EXPIRS [69] for the interpretation of IR spectra. EXPIRS provides a hierarchical organization of the characteristic groups that are recognized by peak detection in discrete ames. Penchev et al. [70] recently introduced a computer system that performs searches in spectral libraries and systematic analysis of mixture spectra. It is able to classify IR spectra with the aid of linear discriminant analysis, artificial neural networks, and the method of fe-nearest neighbors. 

Decades of combined spectral and chemistry expertise have led to vast collections of searchable user databases containing over 300 000 UV, IR, Raman and NMR spectra, covering pure compounds, a broad range of commercial products and special libraries for applications in polymer chemistry (cf. Section 1.4.3). Spectral libraries are now on the hard disks of computers. Interpretation of spectra is frequently made only by computer-aided search for the nearest match in a digitised library. The spectroscopic literature has been used to establish computer-driven assignment programs (artificial intelligence). 

The El source has been the most widely used ion source over the past 60 years and continues to be the method of choice for the analysis (either qualitative or quantitative) of small- to medium-sized volatile organic compounds. The inherent reproducibility of the mass spectra has enabled the assembly of large spectral libraries. Computers associated with current generation instruments can efficiently (in a few seconds) search an unknown mass spectrum against tens of thousands of reference spectra in order to aid in the identification of an analyte. The general scheme of an El source includes the introduction of the vaporized analyte molecules into the ionization chamber, exposure of those molecules... 

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