Spectral match value

Identification involves the confirmation of a certain chemical entity from its spectrum by matching against the components of a spectral library using an appropriate measure of similarity such as the correlation coefficient, also known as the spectral match value (SMV). SMV is the cosine of the angle formed by the vectors of the spectram for the sample and the average spectrum for each product included in the library. 

SMV spectral match value VCSEL vertical cavity surface-emitting... 

What this actually means is the nearer the spectral match value is to 1.000, the better the correlation. Correlations near 1.000 are generated from spectra that are similar but offset. The lower the index the poorer the correlation, through to -1.000 when the spectra are mirror images (Fig. 9.24). 

Fig. 9.3. Semilog plot of the number of structures generated in run 1 (no restrictions black area), run 2 (MOLGEN-MS and NIST substructures grey area) and run 3 with additional filtering using spectral match values and log JCgw information. The number in the x -axis corresponds with the spectrum number, given in [283] and the supporting information of [285]. Reproduced from [285] copyright (2008), with permission from Elsevier.

As was seen in the previous section, substructure classifiers are only one step in reducing the number of structures generated during CASE. Eigure 9.3 demonstrates that mass spectral match value and partitioning behavior reduced candidate numbers further, although many cases with more than 10 possible structures remained even within this small subset of 71 spectra. In terms of positive identification, even 10 possible structures is too many and would mean the purchase (or synthesis) of these reference compounds before a complete identification could be made. This is obviously... 

Several who joined the program were contributors others did not have the requisite background and in spite of enthusiasms were of little value. Dr. Robert L. Cohen was one of the contributors he had the job of selecting a HABI that was most effective with the commercially available filters that would be useful with our dual-response imaging system. He found the best spectral match was with CDM-HABI. 

Rgure 8 Multiple recorded spectral lines can be matched to reference values by recording the intersection of each with the membership function associated with each reference value. An overall match value can be gained by, for example, averaging the membership function values for each line. 

Reference material ISO defines a reference material as a material or substance one of more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials . In spectroscopic applications, these materials are usually substances with known, and proven spectral characteristics. They are invaluable in providing spectral data for either qualitative comparison by spectral matching or spectrophotometer qualification. 

Another often used algorithm for simple spectral matching is the vector correlation method. It is similar to the Euclidean distance method but does not require that the spectra be normalized. In this method, each spectrum is centered around the mean response value to calculate the hit quality index. 

The actual mathematics of the Mahalanobis distance calculation has been known for some time. In fact, this method has been applied successfully for spectral discrimination in a number of cases (Refs. 33-36). One of the main reasons the Mahalanobis distance method was chosen is that it is very sensitive to intervariable changes in the calibration data. In addition, the distance is measured in terms of standard deviations from the mean of the training samples. Not only does the calculation give a very sensitive discrimination but also the reported matching values give a statistical measure of how well the spectrum of the unknown sample matches (or does not match) the original training spectra. 

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 ,... 

CO oxidation reaction. The spectral changes in Cluster C are followed hy Cluster B reduction with a rate constant that is similar to the steady-state value. On the other hand, the rate of formation of the characteristic EPR signal for the CO adduct at Cluster A is much slower. Its rate constant matches that for acetyl-CoA synthesis, hut is several orders of magnitude slower than CO oxidation. Therefore, it was proposed that the following steps are involved in CO oxidation (1) CO hinds to Cluster C, (2) EPR spectral changes in Cluster C are accompanied hy oxidation of CO to CO2 hy Cluster C, (3) Cluster C reduces Cluster B, and (4) Cluster B couples to external electron acceptors (133). 

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