Probability based match search

F. E. McLafferty. This algorithm, called Probability Based Matching or PBM, employs a large number of fragment ions in a reverse search mode (4) to provide reliable identification and quantitation of an individual, specific compound even though the mass spectral measurements are derived from a mixture of two or more compounds (5). 

In practice, the analyte spectrum is entered into the computer, which compares it to the spectra in the stored database using a search algorithm. There are a number of algorithms currently available, including Probability Based Matching, designed by Professor... 

Three different mass spectrometry search algorithms dominate the database searching systems commercially available today. The Cornell University Probability Based Matching (PBM) software, The Integrated Control System (INCOS) and the MassLib system (see below) with the SISCOM search software. 

A completely different search strategy forms the basis of the PBM algorithm (probability based match). The statistical mathematical treatment by Prof. McLafferty allows predictions to be made on the probable identity of a substance suggestion (Atwater et al, 1985 Palisade Corporation, 1994). The search procedure was developed in the 1970s at Cornell University as part of the Cornell algorithm (STIRS, the self-training interpretative and retrieval system as an interpretative system). In the subsequent years, parts of the PBM procedure... 

R.D., and Peterson, D.W. (1985b) Probability-based-matching algorithm with forward searching capabilities for matching unknown mass spectra of mixtures. Anal. Chem., 57, 1056-1060. 

Probability based match, library search procedure for mass spectra developed by Prof McLafferty. 

The information in Table 4.1 indicates that the unknown liquid is most likely l-chloro-2-methylbenzene since the probability of a correct match is placed at 94%. It is interesting to note that the meta and para isomers show probabilities of 70% and 60%, respectively. It is tempting to simply accept the results of the computer-based library search as correct, but the method is not an absolute guarantee that the identity of a sample has been correctly determined. A visual inspection of the experimental and library spectra must be included as part of the process. A computer can compare a mass spectrum it has determined with the spectra in these databases. 

Mascot is another popular database-searching program that emphasizes the quality of the match using a probability-based approach to peptide identification. In contrast to... 

More frequently than chemical techniques, the spectroscopic methods of analysis are used for the determination of polymer chemical composition. Among these techniques the use of infrared (IR) absorption spectra as fingerprints for polymer identification is probably the most common. The IR absorption is produced tjy the transition of the molecules from one vibrational quantum state into another, and most polymers generate characteristic spectra. Large databases containing polymer spectra (typically obtained using Fourier transform infra-red spectroscopy or FTIR) are available, and modern instruments have efficient search routines for polymer identification based on matching an unknown spectrum with those from the library. For specific polymers, the IR spectra can reveal even some subtle composition characteristics such as interactions between polymer molecules in polymeric blends. 

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