Library searches retention index

The retention index system has the advantage of being based on readily available reference materials that cover a wide boiling range. In addition, the temperature dependence of retention indexes is relatively small. In 1984 Sadtier Research Laboratories introduced a library of retention indexes measured on four types of fused-silica open tubular columns. The computerized format of the database allows retention index searching and possible identity recall with a desktop computer. Measurement of retention indexes is the basis of the Rohrschneider-McReynolds scheme for classification of stationary phases in GC (see Section 27C-4),... 

Retention index library mass chromatography interpretation and search for specific chemical shifts and couplings... 

Figure 1.22. GC-MS-computer total ionization-retention index plot obtained from a urine extract from a comatose patient. Labelled peaks indicate library search results and the identification of methadone, methaqualone and their metabolites (reproduced from reference...

Kallio et al. developed an automated procedure for the identification of individual compounds in atmospheric samples and used it for the data analysis of rural aerosol samples [32]. In this procedure, retention indexes, quality parameters (minimum required similarity, S/N value, allowed I difference between experimental and library values), modulation parameters, library files, and retention times of reference compounds were utilized to construct a program for data analysis. As output, the program listed compounds that fulfilled the required criteria. The automated procedure was compared with manual identification, and it was concluded that the automated procedure worked satisfactorily if the concentrations were sufficiently high (above ca. 10 ng/m ), but for very low concentrations (low ng/m ) manual search was more accurate. 

The concept of a reproducibility-based similarity index will be introduced for a simple one-dimensional (fictitious) example. Suppose we want to identify a compound which we already know is a methylpentanol isomer, by library search based on gas-chromatographic data. We have measured a retention value of 740 units with a standard deviation of 5 units. The following small library of reference data is available. 

Fig. 4. Mass spectrum of the peak with the retention time of 10.72 min. From the NIST library search, the compoimd was matched with 2-phenylethanol (phenylethyl alcohol) with 932 similar index (SI).

The results of the GCO run can be searched against this library, giving the user an additional tool for identification (Fig. 4). Any of the custom parameters can be searched. The retention indexes are used to narrow the search. Search within results helps narrow the number of hits. 

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