The PBM Search Procedure

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 

The main search in the PBM procedure can be carried out in two ways. In the pure search mode, only the fragments of the unknown spectrum are searched for in the reference spectra and compared (forward search). This procedure requires mass spectra, which are free from overlap and matrix signals. This only is the case with simple separations at a medium concentration range. 

The sorting of results from the PBM search procedure takes place on the basis of probabilities which are determined in the course of spectrum comparison (Table 3.5). In the forefront is the aim of giving a statement about the identity of a suggestion. The assignment to class I gives information as to which degree 

Class I The probability that the suggestion is identical or a stereoisomer 

Class IV Extension of the probability from class I to compounds having structural differences compared with the reference, which only have a small effect on the mass spectrum (homologues, positional isomers) 

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A mode of the PBM search procedure, which only uses the forward search capability of the library search, -> also Forward Hbrary search. 

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