Physicochemical parameters reversed-phase

The influence of various structural and physicochemical parameters of the stationary and mobile phases on the tailing of a cationic dye in reversed-phase chromatography has been studied in detail. Measurements were performed in a C8 reversed-phase column (80 X 4.6 mm). The isocratic mobile phase was ACN-0.01 M aqueous HC1 (90 10, v/v). Analyses were carried out at 20°C and the flow rate was 1-5 ml/min. The concentration of the cationic dye, l,l -didodecyl-3,3,3, 3 -tetramethylindocarbocyanine perchlorate (Dil) in the model solutions varied between 0.9-309 pM. The dependence of the chromatographic profile of the dye on the injected concentration is illustrated in Fig. 3.112. Calculations and mathematical modelling indicated that the peak tailing of the dye can be... 

T. Cserhati, E. Forgacs and S. Balogh, Relationship between the reversed-phase retention of monotetrazolium and ditetrazolium salts and their physicochemical parameters. J. Planar Chromatogr.-Mod. TLC, 12 (1999) 446 451. 

In spite of widespread applications, the exact mechanism of retention in reversed-phase chromatography is still controversial. Various theoretical models of retention for RPC were suggested, such as the model using the Hildebrand solubility parameter theory [32,51-53], or the model supported by the concept of molecular connectivity [54], models based on the solvophobic theory [55,56) or on the molecular statistical theory [57j. Unfortunately, sophisticated models introduce a number of physicochemical constants, which are often not known or are difficult and time-consuming to determine, so that such models are not very suitable for rapid prediction of retention data. 

That is to say, prediction of retention in reversed-phase LC can be made, based on the premise that relationships exist between the physicochemical parameters representing the molecular properties of the solute suc as structure, shape and/or electronic states etc., and its retention, if suc parameters are available. The baisic concept is shown in equation-1 ... 

The accuracy of this system is dependent on the correlation coefficient of a retention description obtained from studies of QSRR, therefore, the selection of descriptors is the most basic and important task to construct RPS. This selection could be done with statistical framework, even if such description is not clearly derived from theories. The retention description obtained from QSRR studies is more effective for a rapid and accurate prediction of retention than that derived from theoretical models, because the former is simple and does not require introduction of a number of physicochemical parameters (they are often not clearly known and are very difficult and time-consuming to determine) for the latter case. By contrast, the consideration of physical meanings of descriptors derived from QSRR studies gave the overview of retention mechanisms in reversed-phase LC (7-10). That is to say, hydrophobicity, size and shape of alkyl-benzenes and PAHs are dominate factors controlling their retention. 

Polymers have also been used for the coating of alumina. Thus, maleic acid adsorbed onto the alumina surface was, in situ, polymerized with 1-octadecene and cross-linked with l,4-divinylbenzene. ° It was assumed that the polymer forms a monolayer on the alumina, forming a reversed-phase surface. This assumption was substantiated by results showing that the retention order of model compounds was the same as on an ODS column. The lower separation capacity of the new stationary phase was tentatively explained by the lower surface porosity of alumina. Principal component analysis was employed for the elucidation of the relationship between the retention behavior of non-homologous series of solutes on polybutadiene (PBD)-coated alumina and their physicochemical parameters.Calculations revealed significant relationships... 

The reversed-flow gas chromatography (RFGC) technique, a subtechnique of the inverse gas chromatography (IGC), can be used for the determination of physicochemical quantities pertaining to environment and pollutants. Experimental setup and appropriate mathematical analysis for the calculation of physicochemical parameters are reviewed, taking into account i) the interaction between air pollutant(s) and a solid surface in the absence, or in the presence, of a chemical reaction between two pollutants in the gas phase over the solid material (synergistic effects) and ii) exchange of gas pollutant(s) between atmospheric and water environment. 

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