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## Journal of the Chilean Chemical Society

##
*versión On-line* ISSN 0717-9707

### J. Chil. Chem. Soc. v.50 n.2 Concepción jun. 2005

#### http://dx.doi.org/10.4067/S0717-97072005000200009

J. Chil. Chem. Soc., 50, N 2 (2005), págs.: 483-487
Department of Inorganic and Analytical Chemistry. Faculty of Chemical Sciences and Pharmaceutical Sciences. University of Chile. Casilla 233. Santiago de Chile. E-mail ecornwel@abello.dic.uchile.cl
Using a model of 27 saturated hydrocarbons, the logarithm retention times relative to n-hexane were correlated with 11 physico-chemical properties. For all correlations studied, where log t The multi-variable regression studies gave significantly smaller Fisher indices than that obtained in the previously indicated relationship. Principal Component Analysis (PCA) applied to all treated variables indicated that only one linear combination exists with a statistically significant value accounting for almost all of the data variability.
The proposal of a topological index For identification analysis using GLC MS, it is important to have a mathematical correlation model with one or more independent physico-chemical variable references, to match the homologue substances used in the GLC analysis and to obtain calculated retention time as another identification method permitting the resolution of troublesome cases, for example, in the analysis of saturated hydrocarbons in which unspecified fragments originate from homologous hydrocarbon compounds. In such cases overlapping peaks exist which obstruct the process of identification analysis There is nothing in the literature to indicate that boiling point as a reference always produces optimal statistical regression parameters for all organic homologue series, with respect to correlation with other physico-chemical references. The aim of this work is to find, for a model set of saturated hydrocarbons, the optimal physico-chemical reference chosen from a set of physico-chemical properties, such that an optimal regression is obtained for a model GLC retention parameter. To achieve that, the correlation matrix of the logarithm of the relative retention time (log t Using Principal Component Analysis (PCA)
The model of 27 saturated hydrocarbons A
The elements of
This regression presents r, F statistical indices that are the highest of all those calculated when doing the linear regression between log t
The equations (2), (3), (4) referred to above, are as follows:
The optimal statistical indices (r, s.d., F) that belong to the following multivariate regression log t
The objective of Principal Component Analysis (PCA) is to reduce the number of variables by obtaining the maximum possible linear combinations from the [ PCA was applied to the original data [ a.- The data of Table 1 from A
where m is the median and s is the standard deviation. With this procedure, spurious information introduced due to the differences in column magnitudes existing in the original matrix [
Each element of matrix [ _{n1} standarized variable is significant and only one equation is possible which accounts for all the original data variability. See equation 6.
The loading factors of PC
The loadings factor I represents the correlation index of each Z standardized variable (equation 6) with respect to the PC
The PC All calculations and procedures were made using Statgraphic
000I.- For a model of 27 saturated hydrocarbons, the linear regression between the logarithm of relative retention time to n-hexane and critical pressure is optimal with respect to regressions obtained with other physico-chemical parameters of the model. 000II.- All the variables used in this study display a close relationship with one another. This is demonstrated by PCA analysis which indicated that only one linear combination is possible. This fact is corroborated by the size of the elements of the correlation matrix. 000III.- For the model proposed, the absolute difference between the experimental log t 000IV.- This study shows that critical pressure is a valid reference for the evaluation of topological indices applied to saturated hydrocarbons. Note: means a function of.
Y greatly appreciate to Victoria Hare Cornwell the Spanish to English translation.
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