Computer-aided optimization of stepwise gradient and multiple-development thin-layer chromatography

Summary Equations for the final R_F values for mobile phase gradient development and gradient multiple development are presented. Computer simulations of gradient development for both modes of thin-layer chromatography are discussed for the preliminary optimization of gradient programs.     

Computer-assisted optimization of selectivity (mobile phase,pH, and ion concentration) in high-perfomance liquid chromatography

A computer-assisted method is presented for optimization of mobile phase composition in reverse-phase and normal-phase HPLC. The method is based on window diagrams, but only three preliminary tests are required. The method is successfully applied to two examples and there is good agreement between predicted and experimental results. Optimal values for ion concentration and pH in ion chromatography from a published optimization method are compared to values calculated using the computer-assisted method presented in this paper. The same results are obtained, but the method presented here is simpler and faster than previously published one.     

Computer-assisted transposition of conditions in high-performance thin-layer chromatography to high-performance liquid chromatography for the separation of pesticides

Summary A computer-assisted method is presented for mobile phase selection for the optimal separation of pesticides by HPTLC and HPLC. The system is based on a plot of solute retention value and separation criterion vs. binary mobile phase composition for graphic optimization. The result of HPTLC can be transposed to HPLC for optimal separation. The transposition equation is given.     

Computer-assisted optimization of pesticides separation by two-dimensional high-performance thin-layer chromatography

Summary A computer-assisted method is presented for optimization of two mobile phase selection for separation of a mixture of eight pesticides in two-dimensional TLC. Optimization of the separation over the experimental region is based on two special polynomial estimations from preliminary runs of two groups. Using D (distance of two spots) as the selection criterion with a two factor statistical scanning technique excellent agreement is obtained between predicted and experimental results.     

Computer-assisted multifactor optimization of selectivity in gas chromatography

Summary A computer-assisted method is presented for the simultaneous multifactor optimization (stationary phase loading, column temperature and carrier gas flow rate) of the analytical conditions for the optimum separation of multicomponent samples in gas chromatography. The optimization of the separation over the experimental region is based on a special polynomial from twelve preliminary experiments using the resolution as the selection criterion. Computer scanning technique was used for optimum selection in three dimensions. Excellent agreement was obtained between the predicted data and the experimental results.     

Selectivity optimization in green chromatography by gradient stationary phase optimized selectivity liquid chromatography

Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to optimize the selectivity of a given separation by using a combination of different stationary phases. Previous work has shown that SOSLC offers excellent possibilities for method development, especially after the recent modification towards linear gradient SOSLC. The present work is aimed at developing and extending the SOSLC approach towards selectivity optimization and method development for green chromatography. Contrary to current LC practices, a green mobile phase (water/ethanol/formic acid) is hereby preselected and the composition of the stationary phase is optimized under a given gradient profile to obtain baseline resolution of all target solutes in the shortest possible analysis time. With the algorithm adapted to the high viscosity property of ethanol, the principle is illustrated with a fast, full baseline resolution for a randomly selected mixture composed of sulphonamides, xanthine alkaloids and steroids.     

Design of mobile phase composition for liquid chromatography with an internal pH gradient

Summary A method is suggested for calculating the mobile phase composition for ion exchange chromatography with an internal pH gradient. An internal pH gradient of the desired steepness can be achieved providing the titration curve of the sorbent is known. The procedure has been verified by use in the design of a mobile phase composed from few anionic buffers for generation of internal pH gradient on a microcolumn packed with a cation exchanger with carboxylic functional groups.     

Advanced simplex optimization of two-factor selectivity by high performance thin-layer chromatography

Summary A computer-assisted mixture design simplex method is presented for optimization of the separation of a mixture of five benzoic acid derivatives in reversephase HPTLC and twelve PTH-amino acids in normal phase HPTLC. A two-factor selectivity rectangle concept was used. The method is based on a special polynomial estimated from nine experimental runs, using the R_F difference as the selection criterion, with connection to a general simplex method for optimization using a microcomputer. Excellent agreement is obtained between predicted data and experimental results, and more than half the number of experiments required in the general simplex method can be omitted.     

Computerized optimization of gradient elution conditions with ternary solvent mobile phases in RPLC

Summary In this work, an optimization procedure for gradient RPLC separation, using ternary mobile phases, is described. This procedure requires eight preliminary experiments in gradient elution mode to predict the retention surface for each solute over the whole triangular space. This is followed by computerized calculations to determine the best ternary gradient elution profile with respect to both selectivity and analysis time. The efficiency of this procedure from the point of view of rapidity and of accuracy, is illustrated for the specific separation of twelve phenyl urea herbicides.     

Statistical scanning method for the optimization of gradient elution high performance liquid chromatography

Summary A computer-assisted method is presented for the optimization of separation in gradient elution reversed-phase HPLC. The method is based on a polynomial estimation from nine preliminary experiments according to a two-factor (initial solvent composition C and gradient time T) rectangular design. This is followed by a two-dimension computer scanning technique. Resolution is used as the selection criterion. Good agreement was obtained between predicted data and experimental results.     

Influence of development distance on resolution in thin-layer chromatography

Theoretical equations are given to relate resolution with development distance. Comparative experiments undertaken with quaternary ammonium compounds as test substances and using a selection of basic drugs are presented. As expected, resolution decreases with shorter development distance. However, this effect is less pronounced for compounds with small R_f values and when the spot size at the starting point is kept small. It was also shown that, for correctly assessing resolution in relation to development distance, the amounts of material spotted have to be decreased for shorter development distances.     

Axial temperature gradient and mobile phase gradient in microcolumn high-performance liquid chromatography

The effect of axial temperature gradient (ATG) along a microcolumn on the separation performance at both isocratic and gradient elution mode was investigated. A thermostat system was designed to form an ATG along the packed column. Polycyclic aromatic hydrocarbons (PAHs) were separated on a 0.53 mm  × 150 mm i.d. 5 μm C₁₈ microcolumn, with water and acetonitrile as mobile phase. The separation results obtained at mobile phase gradient (MPG) and ATG in microcolumn HPLC were compared with the results performed at ambient conditions. Extrapolated curves of peak width at half height (wh)versus lnk showed that wh is narrower at the same retention time when ATG was applied in addition to MPG. The column efficiency was enhanced 20-30% and the resolution was slightly reduced because of reduction of selectivity at elevated temperature at ATG condition. The RSD of retention time in ATG mode was less than 2.5%.     

Computer-aided optimization of stepwise gradient profiles in thin-layer chromatography

Summary Two mixtures, one containing model coloured solutes and the other glycosides from the Digitalis species were separated by stepwise gradient thin-layer chromatography, the first in the system silica-toluene + ethyl acetate, the second in the system silica-ethyl acetate + methanol. The optimal gradient programs (i.e., for which maximal spread of spots along the plate is observed) were determined using a computer program reported in an earlier paper. Good separation and satisfactory agreement of predicted and experimental R_F values were obtained; the non-aqueous system for the separation of lanatosides permits considerable shortening of elution time owing to the lower viscosity of ethyl acetate-methanol mixtures.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Retention behaviour of some coumarins in normal-phase high-performance thin-layer and column chromatography

Summary A number of coumarins, furocoumarins and pyranocoumarins were investigated using HPTLC and HPLC systems consisting of silica gel and binary and ternary solvents containing a polar modifier (acetonitrile, dioxane, diisopropyl ether, methyl ethyl ketone, ethyl acetate, 2-propanol or tetrahydrofuran) and a non-polar or weakly polar diluent (n-heptane or dichloromethane). The experimental results obtained on thin layers, under isocratic conditions, showed a linear relationship between the R_M values and the log of the concentration of the polar modifier.The influence of the modifier and the individual substituents in the solute molecule on retention is presented as chromatographic spectra by plotting the R_M and logk values against the mobile phase used.Preliminary communication of this work was presented at the 46th International Congress of Pharmaceutical Sciences, in Helsinki, Finland, 1–5 September, 1986.     

Retention prediction of polycyclic aromatic hydrocarbons in reversed phase liquid chromatography with various mobile phase compositions and column temperatures

Summary The relationship between the logarithmic capacity factor measured in reversed-phase liquid chromatography and the operating conditions including the mobile phase composition and the column temperature is investigated. The strategy described herein can offer the possibility to predict the retention of polycyclic aromatic hydrocarbons without any experiments and standard materials, by utilizing equations describing the relationships between retention, temperature, mobile phase composition and physicochemical properties of the solutes previously stored in the program of the microcomputer-assisted retention prediction system.This concept is one of the most promising techniques for the optimization of the separation conditions in reversed-phase liquid chromatography.     

The use of vacuum in thin-layer chromatography with a forced flow of the mobile phase on plates with covered polymer layer

A new version of TLC with a forced flow of the mobile phase has been suggested. The variant involves the use of a TLC plate, the sorption layer on which is covered with a polymer film, and evacuation as an additional driving force for the mobile phase. The advantages of the new method were analyzed; the velocity coefficient of the movement of the mobile phase front was found to be linearly dependent on the rarefaction at the end of the plate.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1143–1146, May, 1996.     

Optimization of the mobile phase composition in gradient elution reversed-phase HPLC by stochastic prediction

Summary Quantitative analysis of more than ten compounds in a sample generally requires complex mobile phases to optimize the separation of the analytes by gradient elution reversed-phase HPLC. For this purpose, CHEOPS, a software package has been developed from the fully stochastic Computer Chromatogram Simulation Method. Calculation principles and optimization criteria are described. Experimental validation is presented with amino acids and steroids.     

The role of the mobile phase in the resolution of racemic esters of aminoacids by normal phase high-performance liquid chromatography

Summary The work in this paper demonstrates the effect of the mobile phase composition on interactions involving racemic esters of aminoacids and a chiral stationary phase derived from N-formylisoleucine. Aprotic solvents have been employed to test the resolution of these racemates. An increase in the alcohol concentration of the mobile phase results in the deterioration of selectivity. These solvents seem to favour high separation factors. The solvent 1,1,2-trichlorotri fluoroethane is a suitable mobile phase modifier for normal phase liquid chromatographic resolution of enantiomers of aminoacid esters.     

Parameters influencing theoretical determination of RM-values of naphthalene derivatives in thin-layer chromatography by using binary mobile phase

The purpose of the studies being carried out is to find some regularities of a general character which determine the relationship between the structures of the chromatographed substances and the composition of the mobile phase, i.e., between the log of the partition coefficient of the sample (A_z), the K₁-values which characterize the adsorption equilibrium of component “1” in a given chromatographic system, the structures of the mobile phase components and the structures of the substances being chromatographed. This paper deals with the relationship between the A_z and K₁ parameters and the structure of naphthalene and a number of its derivatives. It has been shown that there is a close relationship between the kind, size, frequency and site of the substituent on the one hand and the A_z and K₁ values on the other. In order to eliminate the possibility of unwanted side effects, the investigations were carried exclusively using non-active binary mobile phases of the type N + N or N + /B/. From these investigations, a comparison between the parameter A_z and the surface of adsorbed molecules (A_s) was also possible.