Search mode, reverse

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). 

For reverse library searching, a limited library of standard compounds, all of which are expected to be present in the sample, is searched against the unknown spectrum in the current analysis. This search mode is an expansion of normal calibration procedures used currently in HPLC. Each peak of interest in a sample should be characterized through analysis of a standard. The spectral library, consequently, contains spectra for a limited number of... 

Library search is usually performed in the "forward" mode, i.e., by comparing the coded spectrum of interest to every single spectrum within the library. The method of "reverse" search, i.e. comparing each library to the unknown, is slower but allows the detection of small components (poorly resolved) in mixtures (14). 

Several of the porphyrin-containing systems bearing alligator clips did not possess significantly non-linear I(V) characteristics in both the forward and reverse bias modes when studied in the nanopores. But we have yet to test the metal-containing porphyrins. Although our device studies on the porphyrins have not afforded positive results, these observations were specifically found in the nanopore using a selected set of symmetric structures and should not be used to exclude the search for other porphyrin-based molecular electronic devices. Related structures have found efficacy in the studies by Lindsey and... 

Two values are determined for spectral comparison as a result of the main search. The reverse match value (NIST RSI , former INCOS FIT ) value gives a measure of how well the reference spectrum is represented with its masses in the unknown spectrum (reverse search procedure, ignoring all peaks that are in the sample spectrum but not the reference spectrum). The forward looking mode of searching, whereby the presence of the unknown spectrum in the reference spectrum is examined (forward search procedure, all peaks of the sample spectrum are compared), is expressed as the match value (NIST SI ,... 

Thus, in both transversal directions a 1 D-mode search, cf. Eq.(7), does apply subsequently, which is easily performed by TMM. From Fig. 5 it is intuitively clear that TE and TM is reversed for the mode calculations in y and X. Taking this into account, polarization effects are incorporated into EIM to some extent. 

If a training has been performed in reverse mode, a descriptor command will be available — instead of a property command — which opens a chart containing a comparison of two descriptors. In contrast to a property vector, a descriptor can be directly searched for in a binary descriptor database (e.g., to search for corresponding structures). The result window contains then a hit list and two three-dimensional molecule models one displaying the original molecule of the test set entry (if available), and the other showing the molecule of the actually selected entry in the hit list of similar molecules. 

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