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The dead time determination with the spreadsheet method has been conducted on the HPLC system with 2-alkanones homolog series, eluted with several composition ratios of acetonitrile/water solvent. The accuracy of the spreadsheet method is compared against the iteration method, according to the principle of (1) the smallest dead time; (2) the smallest standard deviation of the different dead time values given by the different solvent composition ratios; and (3) the highest linearity of the correlation between the natural logarithm of capacity factor ln(k') versus carbon number nc. The comparison results suggest that the spreadsheet method has equally good criteria with the iteration method. The use of acetonitrile/water solvent exhibits the improved accuracy of the dead time determination with smaller dead time values and standard deviation than the ones given by the methanol/water solvent. [ABSTRACT FROM AUTHOR]

We have used a variety of physicochemical systems, including water‐solvent partitions, solubility in non‐aqueous solvents, and HPLC and gas chromatographic retentions to obtain descriptors for nitro compounds and high energy compounds. These descriptors can then be used to predict a wide range of other physicochemical properties as well as thermodynamic and environmental properties. We illustrate the latter by predictions of the vapor pressure of sublimation, the enthalpy of sublimation and the heat capacity of sublimation at 298.15 K, and predictions of human skin permeability from water. With respect to the obtained descriptors, the most startling finding is that cyclic high energy compounds, with no 'active' hydrogen atom, have a substantial 'hydrogen bond' acidity. We suggest that this is due to electron‐deficient ring systems that act as Lewis acids. [ABSTRACT FROM AUTHOR]

In gas chromatography, for the analysis, the most important thing is the well-chosen column. After having decided about which stationary phase is the best for our measurement and we know the length, the inner diameter and film thickness, we can buy the column from a lot of manufacturers. The products of these manufacturers' look similar to each other, but they are different, because of the different manufacturing technologies. These differences could have significant influence on the separation. It is so important to compare the „same" columns, despite the manufacturers' efforts to produce the best quality columns. 5% diphenyl - 95% dimethyl polysiloxane stationary phase is widely used. Its slight polarity makes it able to determine very different compounds from the alkanes, through volatiles, drugs, fatty acid methyl esters, amines or phenols. In our work, we tested 5% diphenyl - 95% dimethyl polysiloxane stationary phase columns with an 8-component mixture. These columns were from different manufacturers. During isothermal conditions, we determined the height equivalent of theoretical plates on 8 linear velocity level. We represented these parameters as the function of linear velocity. With a constant linear velocity, we measured the excess sorption enthalpy and entropy. From the chromatograms we spotted differences in the retention and in resolution, which is important if we use the column for volatiles or for complex samples. With these parameters we can show many differences between the columns. These parameters have significant influence when we want to use our column for a given task. [ABSTRACT FROM AUTHOR]

The Kovats retention indexes of 51 flavor and fragrance compounds are determined using optimal molecular descriptor data. The genetic algorithm, built with Perl, is used to select the optimum molecular descriptor. The optimal molecular descriptor is used to predict the Kovats retention index with a multiple linear regression created with R. The determination of the molecular descriptor value can be efficiently conducted with free (open source) Online Chemical Database software. Both Perl and R are also free software. The results demonstrate that the 51 flavor and fragrance compounds give 170 molecular descriptors. Among those molecular descriptors, the optimal six are selected based on 200 repetitions in order to build a multiple linear regression (MLR). The best model is selected, and the optimization indicator has an RSquare value of 0.981, Adjusted R-Square value of 0.978 and root mean square error (RMSE) value of 43.50. The constructed genetic algorithm-multiple linear regression (GA-MLR) model can also predict the Kovats retention index with a differences average of 6.6%. The obtained results demonstrate that the GA-MLR method can predict the Kovats retention index. [ABSTRACT FROM AUTHOR]

In reversed phase liquid chromatography (RP-LC), the validity of a multiparametric (MP) non-linear least-squares regression iterative method has been evaluated for 14 different aqueous mobile phases modified with one, two or three organic solvents [acetonitrile (ACN), methanol (MeOH), or tetrahydrofuran (THF)] for calculating the retention time of unretained compound t and the regression parameter (slope b), based on the use of alkan-2-ones and alkyl aryl ketones homologous series. The determination of t and b has been studied for eight binary (ACN-HO or MeOH-HO), 3 ternary (ACN-MeOH-HO) and 3 quaternary (ACN-MeOH-THF-HO) mobile phase systems on an Omnispher C column. The multiparametric calculated t and b values were compared with those obtained by Guardino's, and Grobler's methods. The MP retention indices (RI) of ten monosubstituted benzenes with different functionality (hydroxyl, carbonyl, nitro, etc.) based on the alkan-2-ones retention index standards have been determined and compared for the different mobile phase compositions studied. The influence of organic modifier type, the nature of mobile phase system and water content on the variation of retention parameter studied in this work were discussed. [ABSTRACT FROM AUTHOR]

This work deals with the investigation of the possibilities and limitations using a commercially available software package Drylab for the fast optimisation of running conditions and the prediction of separation and retention times of a mixture consisting of fourteen neutral (nitramines, aminonitroaromatics and nitroaromatics) and six acidic (nitrophenols) explosive-related compounds. Especially the influence of some important experimental parameters, as the concentration of organic modifier in mobile phase or aqueous mobile phase pH value on the prediction of retention times was investigated. The portability of these results onto other columns packed with different, but nominally identical octadecyl-modified silica (C18) packing materials or obtained from different manufactures, were also discussed. Using the computer simulation program Drylab made it possible to find the best separation conditions quickly, e.g. within two runs for composition and three runs for pH value of the mobile phase and without testing a large number of possible chromatographic conditions. The optimization resulted in resolution R 5>1.5 for all explosives and related compounds investigated. The correlation between the simulated run with the theoretical optimum and the final experiment was satisfactory in spite of changes of methanol concentration in the mobile phase or its pH value. Good agreement between experimentally obtained and computer-predicted retention times were found. The average difference do not exceed 5% in most cases. [ABSTRACT FROM AUTHOR]