More information on NIST Mass Spectral Library may be found at www.NISTMassSpecLibrary.com. The GC Methods/Retention Indices library has been extended by including summary statistical analysis of all data in the record. This information will be displayed in the spectrum text information even if the Retention Indices box is unchecked in the properties box. The summary data are given in terms of the type of column (standard non-polar(DB-1), semi-standard non-polar(DB-5), or polar(carbowax)), the median value of the retention data for that column type, the deviation and the number of experimental determinations. Note the deviation is calculated as the median absolute deviation. In the example below (for 6,6-Dimethyl-2-methylenebicyclo[3.1.1]heptan-3-ol or pinocarveol), there are 13 values for the DB5 series of data, 9 for the DB 1 and 12 for the polar column with median absolute deviaions of 4,7 and 8 respectively.
The data will also optionally be shown in the hit list, and the column that will be shown is user selectable.
The Retention Indices checkbox controls the display of the detailed experimental data. The number of GC Methods/Retention Indices displayed is controlled by selecting All or First and entering the number of values to be displayed. The default is to display the first two values. Displaying all values will cause the display to be slow if there are a very large number of literature values.
In addition, for many compounds, an Estimated Kovats Retention Index will be displayed based on the structure associated with the spectrum. These values are reported in index units (iu) with a confidence interval; e.g., “Confidence interval (Ketones): 57(50%) 246(95%) iu” reported for acetone. This means that there is a 50% probability the true value falls within 57 iu of the estimated value and 95% of the time the true value falls within 246 iu of the estimated value. The analysis is based on error measurements of all the data for the class of the compound given; i.e., in this example, ketones. These estimates only display if Retention Indices has been checked in the properties box. The estimates are not displayed in hit lists. If spectra in a user library have associated structures, an Estimated Kovats RI may also be listed for these spectra if the calculation is possible.
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