Wojciech Zapała

Modeling of thermal processes in high pressure liquid chromatography: I. Low pressure onset of thermal heterogeneity

Heat due to viscous friction is generated in chromatographic columns. When these columns are operated at high flow rates, under a high inlet pressure, this heat causes the formation of significant axial and radial temperature gradients. Consequently, these columns become heterogeneous and several physico-chemical parameters, including the retention factors and the parameters of the mass transfer kinetics of analytes are no longer constant along and across the columns. A robust modeling of the distributions of the physico-chemical parameters allows the analysis of the impact of the heat generated on column performance. We developed a new model of the coupled heat and mass transfers in chromatographic columns, calculated the axial and radial temperature distributions in a column, and derived the distributions of the viscosity and the density of the mobile phase, hence of the axial and radial mobile phase velocities. The coupling of the mass and the heat balances in chromatographic columns was used to model the migration of a compound band under linear conditions. This process yielded the elution band profiles of analytes, hence the column efficiency under two different sets of experimental conditions: (1) the column is operated under natural convection conditions; (2) the column is dipped in a stream of thermostated fluid. The calculated results show that the column efficiency is remarkably lower in the second than in the first case. The inconvenience of maintaining constant the temperature of the column wall (case 2) is that retention factors and mobile phase velocities vary much more significantly across the column than if the column is kept under natural convection conditions (case 1).

Synthesis, spectral and thermal study of La(III), Nd(III), Sm(III), Eu(III), Gd(III) and Tb(III) complexes with mefenamic acid

New binuclear complexes of La(III), Nd(III), Sm(III), Eu(III), Gd(III) and Tb(III) ions with mefenamic acid were obtained in solid phase. For all compounds considered, complexation occurs at pH 6–6.5. The analyzed complexes were characterized on the basis of chemical and elemental analyses, molar conductance, UV–Vis, IR and 1H NMR spectroscopies as well as thermoanalytical techniques. According to the research results, the molecular formula of the complexes is Ln2(C15H14NO2)3(OH)3×nH2O, with the exception of the La(III) complex which has the formula La2(C15H14NO2)5(OH). The results show that only the carboxyl group is involved in the coordination of the rare earth ions in the bidentate mode. Coordination does not occur through the nitrogen atom. All the complexes are soluble in DMSO, and they are nonelectrolytes. The TG-FTIR technique was employed in order to study a decomposition pathway of the obtained compounds. The received results provide information on the composition, thermal stability, thermal decomposition, as well as the gaseous products that evolved during the thermal decomposition of the considered compounds.

Retention Process in Normal‐Phase TLC Systems

Abstract The influence of mobile phase composition on the retention of selected test analytes in different normal‐phase TLC systems has been studied. A novel adsorption model for an accurate prediction of the analyte retention in the thin‐layer chromatography with binary mobile phase has been proposed. The performance of the model was compared with the retention models reported in the literature. All the models were verified for different TLC systems by three criteria: the sum of squared differences between the experimental and theoretical data, the approximation of the standard deviation, and the Fisher test.

Studies on the sorption behavior of quercetin, phenol, and caffeine as test substances on diol mixed-mode HILIC column

ABSTRACT The influence of mobile phase composition and column temperature on the retention behavior of quercetin (Q), phenol (PH), and caffeine (CAF) as test analytes on diol- Acclaim Mixed Mode HILIC-1 column in mobile phases containing varying fractions of methanol in water and acetonitrile in water was analyzed. Brief analysis of the column efficiency was also presented. Using the frontal analysis (FA) method the adsorption studies at the different mobile phase compositions were undertaken and the adsorption energy distributions (AED) have been calculated prior to selection of proper adsorption model. The calculations revealed heterogeneous interactions for Q and PH in the analyzed systems while homogeneous for CAF in systems with low water content in eluent and heterogeneous in systems with high water content. The Langmuir and bi-Langmuir isotherm turned out to be excellent in description of these adsorption trends. GRAPHICAL ABSTRACT

Investigations of selected properties of pharmacologically active compounds by chromatographic and potentiometric methods on the chrysin example

Investigations of selected properties of pharmacologically active compounds by chromatographic and potentiometric methods on the chrysin example The RP-TLC method was used to determine the dissociation constant of chrysin (5,7-dihydroxyflavone) in methanol-aqueous (1:1 v/v) solutions. In this method the pK value was quantified on the basis of retention data and a retention model. The accuracy of determining the model parameters was analysed using the following statistical criteria: the sum of the squared differences between the experimental and theoretical data, approximation of standard deviation, and the Fisher test. Besides, in this work the potentiometric method was used. Investigations were carried out at ionic strength I=0.1 at T= 298 K. The dissociation constant were determined using the Rossotti method as well as the numerical method based on the procedures of non-linear curve fitting using Microsoft Excel Solver and the user-defined function. It has been found that the differences in the evaluated pK values were relatively small and did not exceed 1.2%.

Brief analysis of the retention process in RP‐HPLC systems with a C30 bonded stationary phase

The influence of the mobile-phase composition on the retention of eight model substances in different RP-HPLC systems with a C(30) alkyl bonded stationary phase has been studied. The aim of this study was to compare the performance of four valuable retention models assuming the partition and adsorption mechanism of retention. All the models were verified for different experimental data by four criteria: the sum of squared differences between the experimental and theoretical data; the approximation of the standard deviation; the Fisher test; and the F-test ratio.

Modeling of the influence of the modifier concentration on the retention process in NP-HPLC

Modeling of the influence of the modifier concentration on the retention process in NP-HPLC The adsorption model for an accurate prediction of the analyte retention in the normal - phase liquid chromatography with a binary mobile phase has been proposed. This model was derived using a thermody-namically consistent modified competitive Langmuir isotherm. The performance of the proposed equation was compared with two retention models reported in literature. All models were verified for different NP-LC systems by use of three criteria: the sum of squared differences between the experimental and theoretical data, approximation of the standard deviation and the Fisher test.