Library Search Programs

In general, it is expected that the identity of an unknown compound will be found in a library search procedure. However, it is better to consider the results of a search procedure from the aspect of similarity between the reference and the unknown spectrum (Stein and Scott, 1994). Other information for confirmation of identity, such as retention time, processing procedure and other spectroscopic data should always be consulted. A review in the journal Analytical Chemistry (Warr, 1993a) began with the sentence. 

Examples of critical cases are different compounds which have the same spectra (isomers), the same compounds with different spectra (measuring conditions, reactivity and decomposition) or the fact that a substance being searched for is not in the library but similar spectra are suggested. In particular, the limited scope of the libraries must be taken into account. 

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Solvents and their impurities represent a wide class of compound types therefore, a discussion of common mass spectral features is meaningless. However, most of the mass spectra are listed in computer library search programs and The Eight Peak Index. ... 

Library search programs allow direct searches to determine whether or not the spectrum that is obtained is present in the collection, or to carry out inverse searches to determine if the spectrum of a given compound in a collection occurs among those recorded during a chromatographic analysis, for example. An example of a library search is given at the end of Chapter 3. 

Many commercially available library search programs use these techniques to generate a list of the most likely matches of the unknown sample. However, there are many problems with this technique. First, search techniques simply identify samples as the materials from the closest matching spectrum in the library. If the library does not contain any spectra of the true compound, it will just report the best match it found regardless of whether it is really even the same class of material. 

Sokolow, S., Karnovsky, J. and Gustafson, P. (1978) The Finnigan Library Search Program. Fiimigan MAT Applikation No. 2. 

The deconvolution step is greatly facilitated by using the AMDIS program and the NIST mass spectral library search program (Mallard and Reed, 1997). Unique compound mass spectra are extracted by the analysis of all the transient ion signals allocating ion masses and relative intensities for each of the eluting compounds. 

NIST Standard Reference Database 1A, NIST/EPA/NIH Mass Spectral Library with Search Program (Data Version NIST 02, Software Version 2.0). 

The OPCW Laboratory performs functional tests on the authenticated, certified, and on-site analytical databases. These are tests that verify that the analytical database is functional. So far, this procedure is fully developed for the MS analytical databases. The electronic version of OCAD (which so far consists of MS analytical data only) is tested with the NIST MS Search/Analysis program. The on-site MS analytical databases are tested using AMDIS software. A NIST or AMDIS library is created and this becomes the target library for a library search. A search is performed on a newly measured MS spectrum (raw data files) containing a number of chemicals that are present in the target library. Identification of the targeted spectrum indicates that the created library is functional. 

Gas Chromatography-Mass Spectrometry. A VG Trio-2 mass spectrometer was directly coupled with the Hewlett-Packard 589 R gas chromatograph, equipped with a 30 m x 0.32 mm DB-WAX capillary column (J and W. Scientific bonded polyethylene glycol phase). The carrier gas was He at 2.3 ml/min. The injector and transfer temperature was programmed as follows 30 C (2 min isothermal), to 38°C at l°C/min, then to 180°C at 2°C/min. The instrument was operated in the electron-impact mode at an ionization voltage of 70eV. Quantitative analysis by peak area, plots of chromatograms, and library search results were obtained. 

The MST/EPA/NIH Mass Spectral Library 1998 database ( www.nist.gov/ srd/analv.htm) is the product of a muftiyear, comprehensive evaluation and expansion of the world s most widely used mass spectral reference library, and is sold in ASCII or Windows versions. It contains 108,000 compounds with electron ionization spectra, chemical structures, and molecular weights. It is available with the NIST MS Search Program for GC/MS deconvolution, MS interpretation, and chemical substructure analysis. The NIST chemistry WebBopk ( http //webbook.nist.gov) is a. free online system that contains the mass spectra of over 12,000 compounds (this Standard Reference Data Program also has IR and UV-Vis spectra). 

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... 

Number of entry. This item is connected with the identification (chronological) number of the spectrum in the user-created library of the Broker IR-search program, modified for working with Raman spectra. This also serves as a chronological number in the original information database (using Microsoft Office )... 

Our hbrary search program, based on this similarity index, allows the specification of a minimum value for the similarity index. If, for example, a threshold value of 1 per cent is specified, references with an SI less than 1 per cent are rejected as possible candidates. For these candidates the null hypothesis is rejected at a significance level (a) of 1 per cent. The output of the retrieval system is a list of compounds (if any) that have SI values above the preset threshold, i.e., compounds for which the null hypothesis is accepted. For the pentanol problem our library search system gives the foUowing output ... 

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