Retention modeling

ESTIMATION OF RETENTION MODELS ADEQUACY IN MICELLAR LIQUID CHROMATOGRAPHY... 

The known models for describing retention factor in whole variable space ar e based on three-phase model and containing from three to six par ameters and variety combinations of two independent factors (micelle concentration, volume fraction of organic modifier). When the retention models are comparing or the accuracy of fitting establishing, the closeness of correlation coefficient to 1 and the sum of the squared residuals or the sum of absolute deviations and their relative values is taken into account. A number of problems ar e appear in this case ... 

Usually goodness of fit is provided by adding new parameters in the model, but it decreases the prediction capability of the retention model and influences on the optimization results of mobile phase composition. 

Different tests for estimation the accuracy of fit and prediction capability of the retention models were investigated in this work. Distribution of the residuals with taking into account their statistical weights chai acterizes the goodness of fit. For the application of statistical weights the scedastic functions of retention factor were constmcted. Was established that random errors of the retention factor k ai e distributed normally that permits to use the statistical criteria for prediction capability and goodness of fit correctly. 

The criteria chai acterizing the robustness of parameters of retention model for the changing of experimental data number were proposed to estimate the prediction capability of the models. 

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

A new type of functional dependence follows from the equation of the conceptual retention model ... 

Y. V. Gankin, A. E. Gorshteyn and A. Robbat-Jr, Identification of PCB congeners by gas chromatography electi on capture detection employing a quantitative sti ucture-retention model , Aim/. Chem. 67 2548-2555 (1995). 

Prus and Kowalska [75] dealt with the optimization of separation quality in adsorption TLC with binary mobile phases of alcohol and hydrocarbons. They used the window diagrams to show the relationships between separation selectivity a and the mobile phase eomposition (volume fraction Xj of 2-propanol) that were caleulated on the basis of equations derived using Soezewiriski and Kowalska approaehes for three solute pairs. At the same time, they eompared the efficiency of the three different approaehes for the optimization of separation selectivity in reversed-phase TLC systems, using RP-2 stationary phase and methanol and water as the binary mobile phase. The window diagrams were performed presenting plots of a vs. volume fraetion Xj derived from the retention models of Snyder, Schoen-makers, and Kowalska [76]. 

As in isocratic mode, the estimate of log P is indirect and based on the construction of a linear retention model between a retention property characteristic of the solute (logkw) and a training set with known logP ci values. To assess the most performing procedures, the three hydrophobicity indexes (( )o, CHI and logkw) were compared on the basis of the solvation equation [41]. These parameters were significantly inter-related with each other, but not identical. Each parameter was related to log P with values between 0.76 and 0.88 for the 55 tested compounds fitting quality associated with the compound nature. 

Figure 4.17 General phenonenaloglcal retention model for a solute that participates in a secondary chemical equilibrium in liquid chromatography. A - solute, X - equilibrant, AX analyte-equilibrant coeplex, Kjq - secondary chemical equilibrium constant, and and are the primary distribution constants for A and AX, respectively, between the mobile and stationary phases.

Yamamoto, A., Hayakawa, K., Matsunaga, A., Mizukami, E., and Miyazaki, M., Retention model of multiple eluent ion chromatography. A priori estimations of analyte capacity factor and peak intensity /. Chromatogr., 627,17,1992. 

Rounds, M. A. and Regnier, F. E., Evaluation of a retention model for high-performance ion-exchange chromatography using two different displacing... 

Madden, J. E. and Haddad, P. R., Critical comparison of retention models for the optimization of the separation of anions in ion chromatography II. Suppressed anion chromatography using carbonate eluents, /. Chromatogr. A, 850, 29, 1999. 

Ng, K.L., Pauli, B., Haddad, P.R., and Tanaka, K., Retention modeling of electrostatic and adsorption effects of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography, /. Chromatogr. A, 850, 17, 1999. 

Mewhinney JA, Griffith WC, Muggenburg BA. 1980. Proposed retention model for human inhalation exposure to 241Am02. In International Radiation Protection Society, ed. Radiation protection A systemic approach to safety Proceedings of the 5th Congress of the International Radiation Protection Society, Jerusalem, March 1980. New York Pergamon Press, 615-618. 

Geng, X., Regnier, F.E. (1984). Retention model for proteins in reversed-phase liquid chromatography. J. Chromatogr. 296, 15-30. 

ICRP (1966). International Commission on Radiological Protection, Deposition and retention models for internal dosimetry of the human respiratory tract, Health Phys. 12,173. 

With just a few exceptions, there is a dearth of published information providing systematic studies of retention volumes as a function of composition of the eluent over the whole composition range of binary solvents. To rectify this situation, a general equation for HPLC binary solvent retention behavior has been proposed [59] that should help generate a chromatographic retention model to fit Eq. (15.20) ... 

G. Vivo-Truyols, J.R. Torres-Lapasio and M.C. Garcia-Alvarez-Coque, Error analysis and performance of different retention models in the transference of data from/to isocratic/gradi-ent elution. J. Chromatogr.A 1018 (2003) 169-181. 

F. Houton, L. Yaoping and X. Minjie, Nonlinear function retention model in weak acid anion chromatography. J. Chromatogr.A 945 (2002) 97-102. 

Hetaeric chromatography, 230, 231 effect of charge on hetaeron, 233 retention model of, 231-238 Hetaeron. 191, 230, 231, 240, 243, 249, 280 see also Complexing agent adsorption on the stationary phase, 231, 249,230 amphiphilic, 243 cetrimide, 248 decylsulfonate, 230 dodecylbenzenesulfonate, 230 formation constant of complexes, 276 lauryl sulfate, 230 metal chelating, 262 micelle formation, 230 optically active, 262 surface concentration of, 232... 

PG Muijselaar, HA Claessens, CA Cramers. Migration behavior of monovalent weak acids in micellar electrokinetic chromatography mobility model versus retention model. J Chromatogr A 765 295—306, 1997. 

The relative retention a=k/ki is a measure of the separation selectivity for two compounds i and j with retention factors ki and kj, respectively, differing by one repeat structural unit, An=l.p in Equation 5.16 is the end-group contribution to the retention factor. The conventional theory describes adequately the retention of oligomers and lower homopolymers and copolymers up to the molar masses 10,000-30,000Da for higher polymers the accuracy of the determination of retention model parameters is too low [95]. 

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