A new possibility for estimating the octanol/water coefficient (log P) was investigated using only one descriptor, the semi-empirical electrotopological index (ISET). The predictability of four octanol/water partition coefficient (log P) calculation models was compared using a set of 131 aliphatic organic compounds from five different classes. Log P values were calculated employing atomic-contribution methods, as in the Ghose/Crippen approach and its later refinement, AlogP; using fragmental methods through the ClogP method; and employing an approach considering the whole molecule using topological indices with the MlogP method. The efficiency and the applicability of the ISET in terms of calculating log P were demonstrated through good statistical quality (r > 0.99; s < 0.18), high internal stability and good predictive ability for an external group of compounds in the same order as the widely used models based on the fragmental method, ClogP, and the atomic contribution method, AlogP, which are among the most used methods of predicting log P.

A new semi-empirical electrotopological index, I SET , for quantitative structure-retention relationships (QSRR) models was developed based on the refinement of the previously published semi-empirical topological index, I ET . We demonstrate that the values of C i fragments that were firstly attributed from the experimental chromatographic retention and theoretical deductions have an excellent relationship with the net atomic charge of the carbon atoms. Thus, the values attributed to the vertices in the hydrogen-suppressed graph of carbon atoms (C i ) are calculated from the correlation of the net atomic charge in each carbon atom, which is obtained from quantum chemical semiempirical calculations, and the C i fragments for primary, secondary, tertiary and quaternary carbon atoms (1.0, 0.9, 0.8 and 0.7, respectively) obtained from the experimental values. This shows that I ET encoded this quantum physical reality and that it is possible to calculate a new I SET (the semi-empirical electrotopological index) through the net atomic charge values obtained from a Mulliken population analysis using the semi-empirical AM1 method and their correlation with the values attributed to the different types of carbon atoms. This demonstrates that the I SET encodes information on the charge distribution of the solute on which dispersive and electrostatic interactions between the solute (alkanes and alkenes) and the stationary phase strongly depend. Thus, this new method can be considered as an initial step towards forthcoming QSRR/QSAR studies.

The semi-empirical electrotopological index, I SET , used for quantitative structure-retention relationship (QSRR) models firstly developed for alkanes and alkenes, was remodeled for organic functions such as ketones and aldehydes. The I SET values for hydrocarbons are calculated through the atomic charge values obtained from a Mulliken population analysis using the semi-empirical AM1 method and their correlation with the SET i values attributed to the different types of carbon atoms according to experimental data. For ketones and aldehydes the interactions between the molecules and the stationary phase are slowly increased relative to the hydrocarbons, due to the charge redistribution that occurs in the presence of heteroatoms. For these polar molecules the increase in the interactions was included in the calculation of the I SET values through the dipole moment of the whole molecule and also through an equivalent local dipole moment related to the net charges of the atoms of the C --O and HC --O functional groups. Our findings show that the best definition of an equivalent local dipole moment is clearly dependent on the specific features of the charge distribution in the polar region of the molecules (e.g. ketones and aldehydes), which allows them to be distinguished. Thus, the QSRR models for 15 aldehydes and 42 ketones obtained using the remodeled I SET were of good quality as shown by the statistical parameters. The ability of this remodeled index to include charge distribution and structural details opens a new way to study the correlations between the molecular structure and retention indices in gas chromatography.

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This study was carried out to show the predictive capacity of the semi-empirical topological index (I ET ) in estimating some important physical properties; melting point, Mp (-C), boiling point, Bp (-C), and experimental log p of halogenated aliphatic hydrocarbons. The retention index (RI) values of 141 compounds were used in the building of this specific model of the I ET . The simple linear regression between RI Exp and the I ET exhibits high quality with a coefficient of determination of r 2 ¼ 0.9995, standard deviation of SD ¼ 8 and leave-one-out cross-validation correlation coefficient of r Finally, for 19 compounds the correlation between the experimental log p-value and that calculated using the I ET method gave a value of r 2 ¼ 0.9871, while the correlation with the value obtained using the most used Fragment Addition Method was r 2 ¼ 0.9750. These results show the predictive capacity of the I ET for these physical properties.

The semi-empirical electrotopological index (I SET ) used for quantitative structure-retention relationship (QSRR) models firstly developed for alkanes and alkenes, was remodeled for different organic compounds such as ketones, aldehydes and esters. In this study, the I SET was developed and optimized to describe the chromatographic retention of aliphatic alcohols on six different stationary phases (SE-30, OV-3, OV-7, OV-11, OV-17 and OV-25). The presence of a hydroxyl group leads to a charge redistribution increasing the interactions between these molecules and the stationary phases relative to the interactions between hydrocarbons and the same stationary phases. These considerations were included in the calculation of I SET . The simple linear regressions (SLR) between retention indices and the I SET for each stationary phase showed good statistical quality, high internal stability and good predictive ability for external groups, especially for stationary phases with low polarity. A single combined model, in which the McReynolds polarity term was added as a descriptor, was developed for all the data points for the stationary phases and the results were of satisfactory predictive quality. The efficiency and the applicability of the approach were demonstrated through the high quality quantitative structure-property relationship (QSPR) model for the boiling point (BP). For this physical property 134 compounds were used; most of them were not included in the original data set employed to develop the I SET .

This paper presents the development of an on-line pre-concentration system to determine cadmium(II) in aqueous samples. The analyte was trapped in a mini-column filled with Al(2)O(3) in the form of macro-spheres obtained by the mixture of Al(NO(3))(3).9H(2)O(aq) and chitosan dissolved in acetic acid. The mixture was dropped into an NH(4)OH aqueous solution under rigorous agitation using a peristaltic pump, the macro-spheres were separated from alkaline solution and dried, and finally were submitted to thermal treatment. The pre-concentration system was linear between 1.0 and 100 microg L(-1), with a linearity of 0.999, sensitivity of 3.58 x 10(-3)L microg(-1) and enrichment factor of 21.9. The limits of detection and quantification were 0.08 microg L(-1) and 0.28 microg L(-1), respectively. The repeatability was between 2.6 and 5.9%. Recovery tests were carried out with a real aqueous sample.