Performance Of Chromatographic System Research Articles

Study on the performance of different types of three-dimensional chromatographic systems

The maximum achievable performance of possible types of three-dimensional chromatographic systems (LC×LC×LC) has been investigated. The Pareto-optimization approach was applied to establish a trade-off between three main objectives (total peak capacity, analysis time and dilution of the sample) and Pareto-front values were obtained. The performances of xLC×xLC×xLC (three-dimensional separation in space), tLC×tLC×tLC (three-dimensional separation in time) and the hybrid xLC×xLC×tLC system were compared mutually and with two-dimensional chromatographic systems. It was found that xLC×xLC×xLC performs best in terms of maximum achievable peak capacity in shortest analysis time. Based on current thin-layer-chromatography performance it should be possible to obtain a peak capacity of 50,000 within 20min. If contemporary column-packing standards can be upheld the achievable limit is approximately 50% higher. However, in an xLC×xLC×xLC chromatographic system analytes remain in the separation domain after the analysis, which complicates the detection. Use of an xLC×xLC×tLC system with elution in the last dimension alleviates the detection problem. The maximum achievable peak capacity in the same analysis time is lower for xLC×xLC×tLC than for xLC×xLC×xLC. Using the same (reasonable) length of the separation domain (e.g. a cube 200×200×200mm) for both systems, it is possible to achieve peak capacities of 78,000 for xLC×xLC×tLC operated in the gradient mode, which is twice higher than for an xLC×xLC×xLC system. A three-dimensional (three-column) time-based tLC×tLC×tLC system does not greatly improve the performance of tLC×tLC in terms of (maximum) peak capacity and (minimum) analysis time. Dilution factors in tLC×tLC×tLC are very high. Decreasing the dilution has a detrimental influence on the peak capacity. The trade-off between these objectives is of crucial importance. The influence of several parameters (length of the separation domain, particle size, etc.) on the performance of chromatographic systems was investigated, optimal ranges were found.

Effect of Flow Rate on Height Equivalent to a Theoretical Plate for Lithium Isotope Separation with Displacement Chromatography

A series of experiments of Li isotope separation with displacement chromatography using a highly porous resin were performed under several flow rates from 0.1 to 20 cm3/min. The flow rates were equivalent to a speed of a moving boundary of 0.0012 to 0.26cm/s. In evaluating Height Equivalent to a Theoretical Plate, HETP, as well as separation factor which indicate separative performance of chromatographic system, we developed a new relationship between HETP and a profile of 6Li mole fraction in the effluent with a mathematical model taking account of a mixing in a free space at the column outlet and in the fractionated samples. The values of separation factor and HETP of each experiment were simultaneously determined by the developed relation. The obtained values of the separation factor agreed with those evaluated by the frontal analysis method within the range of the experimental error. The obtained value of HETP increased with the flow rate in the range of the present experiments. It was suggested that diffusion of Li ion in particles as well as convective mixing of the solution played a significant role on determination of HETP.

Frontal chromatography of proteins: Effect of axial dispersion on column performance

A mathematical model describing the dynamic adsorption of proteins in columns packed with spherical porous adsorbent particles is used to study the effect of axial dispersion on the performance of chromatographic systems. The values of the axial dispersion coefficient, DL, are estimated from a correlation based on a model describing axial dispersion in packed beds that provides satisfactory results when compared with experiment. Simulations of frontal chromatography in systems including axial dispersion and in systems without axial dispersion are made and compared to determine the effect of axial dispersion on the efficiency of the adsorption process; also, the system parameters that influence axial dispersion are examined. It is found that the reduction in the efficiency of the adsorption process due to axial dispersion is small (<1%) for columns of length 10 cm or greater. However, for short columns, this efficiency reduction can be as large as 10%. Increasing the adsorbent particle diameter, dp, increases the magnitude of the reduction in efficiency due to axial dispersion; the effect of increasing the adsorbent particle diameter, dp, is much more pronounced in a short column than in a long column.

Effects of structural and kinetic parameters on the performance of chromatographic columns packed with perfusive and purely diffusive adsorbent particles

A mathematical model describing dynamic adsorption in columns with spherical bidisperse perfusive or spherical bidisperse purely diffusive absorbent particles is used to study the effects of the structural parameters of the adsorbent particles and of the parameters of the adsorption mechanism on the performance of chromatographic systems involving the adsorption of bovine serum albumin onto anion-exchange porous adsorbent particles. Four structural parameters are studied: the particle diameter, d p, the macropore void fraction, ϵ p, the microparticle diameter, d m, and the parameter φ, which affects the value of the permeability of the adsorbent particle. Two parameters of the adsorption mechanism are studied: the maximum equilibrium concentration of adsorbate in the adsorbed phase of the adsorbent particle, C T and the rate constant k 1, which characterizes the adsorption step of the interaction mechanism between the adsorbate molecules and the active sites on the surface of the pores of the adsorbent particles. The performance of columns packed with purely diffusive particles improves when the value of d p is decreased, when the value of ϵ p is increased and when the value of d m is decreased; the effect of d m is much smaller than the effects of d p and ϵ p. Intraparticle flow in perfusive particles can improve column performance of its is of sufficient magnitude; intraparticle flow increases when the value of d p is decreased, when the value of ϵ p is increased, when the value of d m is increased and when the value of φ is decreased. The difference between the performance of a column packed with perfusive particles and that of a column packed with purely diffusive particles will depend upon the particular combination of the parameters d m, ϵ p, d mm and φ. When the value of k 1 is is small, an increase in k 1 improves column performance. However, when the value of k 1 becomes sufficiently large, further increases have no effect on column performance. Increasing the value of C T has a large effect on column performance by increasing the breakthrough time and the mass of adsorbate in the adsorbed phase at breakthrough. The performance of chromatographic systems with purely diffusive particles can be better than the performance of chromatographic systems with perfusive particles, if purely diffusive particles can be made that have higher values of C T than otherwise comparable perfusive particles.