Marie-France Gonnord

Theoretical Investigation of the Potentialities of the Use of a Multidimensional Column in Chromatography

Two-dimensional column chromatography is a method which combines the advantages of column chromatography (constant, adjustable flow velocity, excellent efficiency, on-line detection) and two-dimensional thin-layer chromatography (successive developments in two perpendicular directions, using two different retention mechanisms). It is shown that by merely keeping constant the solvent flow velocity during the development of a thin-layer plate, a considerable increase in the spot capacity can be achieved, since plate length and particle size can be selected without any prejudicial influence on the solvent velocity which can be kept constant at the value considered as optimum by the analyst. Calculations show that two-dimensional column chromatography can generate peak capacities well in excess of 500, up to several thousands, and that the specifications for the equipment are not too stringent. A 10 × 10 cm column would be 1 mm thick, be well packed with 10-μm particles and be operated at a reduced velocity of 10. Such a packing could be expected to be very homogeneous (A = 0.7) and the reduced plate height would be 1.95. The expected spot capacity is 900, while the pressure drop for a compound with a diffusion constant D = 5 × 10-6, cm2/sec (linear velocity, u, = 0.05 cm/sec) and a solvent with viscosity 1 cP is only 5 atm (flow-rate 3 cm3/min). The sample spot should be about 1 mm in diameter or less. Equipment capable of these performances is under construction. Successful operation of this two-dimensional separation scheme, however, relies on the ability to find two chromatographic systems operating according to widely different mechanisms.

Chromatography with a two-dimensional column

SummaryA chromatographic method using a flat, square column developed along one direction and then eluted along the perpendicular direction, using a second retention mechanism widely different from the first one is described. Such a method would offer a potential peak capacity of several thousands, at least ten times more than either conventional column chromatography or two-dimensional thin-layer chromatography. Equipment capable of satisfying the requirements derived from a theoretical study of the operation of a two-dimensional column is also described. Results are satisfactory.

Study of the performances of thin-layer chromatography : VII. Spot capacity in two-dimensional thin-layer chromatography

Abstract In two-dimensional thin-layer chromatography the spot capacity is the number of spots, resolved with a resolution unity, that can be placed on the plate between the two solvent fronts and the parallels to these fronts through the center of the original sample spot. This is difficult to calculate because the plate height in thin-layer chromatography (TLC) is a complex function of the characteristics of the solvents and the plate, since during development in one direction the spots spread in both directions and since calculation of the density of the most dense spot packing requires topological information that is not available. Some simplifying assumptions are made and an iteration method is used. The results show that is very easy to achieve a spot capacity between 100 and 250, but difficult to reach 400 and nearly impossible to exceed 500, except in very favourable circumstances. As for one-dimensional TLC, the spot capacity in two-dimensional TLC increases with decreasing diffusion coefficients and with increasing plate quality (i.e., packing homogeneity) and kinetic coefficients of the solvents. For a given solvent and development length there is an optimum particle size which provides the maximum spot capacity. The development time for a capacity of 300 spots is around 30 min but it is very difficult to obtain accurate quantitative results if the analysis is fast.

Optimized capillary zone electrophoretic separation of chlorinated phenols

Abstract A mixture of thirteen chlorinated phenols was resolved within 16 min by using a 57 cm × 75 μm I.D. fused-silica tube with a 50 m M sodium phosphate buffer (pH 6.9) electrolyte, under an 18 kV potential. The electrophoretic behaviour of chlorophenol congeners was investigated in order to optimize their separation as a function of the running buffer pH, concentration and applied voltage. A migration order depending on both charge and size of the solutes was established. Selectivity is strongly affected by the electrolyte concentration, in a manner that cannot be easily predicted. Quantitative aspects of capillary zone electrophoresis are also discussed.

Computer assistance in the selection of the optimum combination of systems for two-dimensional chromatography

Abstract To permit the selection of the optimum combination of chromatographic systems in two-dimensional chromatography among those available, a data bank has been created on a personal microsystem from k′ of RF values published in the literature or measured in the laboratory. Simulations of two-dimensional chromatograms can be shown on either the system display or on a plotter. The selection of the best pair of chromatographic systems to resolve different compounds from a mixture is performed by the system after selection by the user of an optimization criterion. The pertinence of various criteria is compared.

Gas chromatographic mass spectrometric study on the formation of polychlorinated dibenzo-p-dioxins and polychlorobenzenes from polyvinyl chloride in a municipal incinerator

Abstract Laboratory-scale experiments have indicated that the presence of polychlorinated dibenzo-p-dioxins (PCDDS) and polychlorobenzenes (BPCS) on fly ash from municipal incinerators may be the result of combustion of polyvinyl chloride (PVC). Data shown here are the result of addition of 300% the usual level of PVC to a municipal incinerator. The concentrations of PCDDS and BPCS are compared before and after addition of PVC. No significant differences in the concentrations of these substances on the fly ash were found.

Molecular statistical theory of adsorption prediction of the thermodynamical functions of adsorption of hydrocarbons on graphitized thermal carbon black

Abstract The molecular statistical theory of adsorption has been applied to the calculation of the adsorption equilibrium coefficient, the retention volume, the differential energy and entropy of adsorption on graphite for various hydrocarbons of very different molecular shape, size, and polarizability: quasiplanar molecules like benzene, methyl and polymethylbenzenes, naphthalene, methyl and polymethylnaphthalenes and quasilinear molecules like ethane, propane, n-butane, cis, and trans 2-butenes and 1-butene. The behavior of the molecules studied above the surface of graphite is accounted for using quasirigid models, taking into account their geometrical structure. As n-butane and 1-butene have rotational isomers, it has been assumed that these gases are mixtures of the various conformers at equilibrium. A good agreement is found between the theoretical results and the experimental data derived from gas chromatographic measurements on graphitized thermal carbon black.

Chromatographic determination of gas—solid adsorption isotherms by the step and pulse method: II. Choice of a model for the adsorption isotherm of benzene and cyclohexane on graphitized carbon black

Abstract Different models of adsorption isotherm have been applied to the study of the adsorption of benzene and cyclohexane on graphitized thermal carbon black by the step and pulse gas chromatographic method. It is shown that within the precision of the experimental results, a good description of the adsorption of benzene is obtained with all the models tested, although a polymolecular adsorption mechanism seems preferable. At the low coverage range (θ

Chromatographic determination of gas—solid adsorption isotherms by the step and pulse method: I. Apparatus and data processing

Abstract The step and pulse chromatographic method is applied to the determination of the adsorption isotherm of benzene on graphitized carbon black Sterling MTG. The experimental setup is described. A method of resolution of the mathematical problems inherent to the experimental technique is discussed and its performances are given. The influence of the chromatographic column pressure drop is shown to be well accounted for. The problem of the selection of an equation to represent the adsorption process is raised.

Simple techniques for two-dimensional gas chromatography

Abstract The adaption of the Deans system of double-column gas chromatography for use with a commercial chromatograph is described. Optimization of the carrier gas flow-rates through the two columns is achieved independently in each column. The importance of using an intermediate trap between the two columns is demonstrated. A system for automatic rejection of the major components of the analyzed mixture is described. Quantitative analysis of trace impurities has been performed using a suitable calibration.