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Selected papers from the latest issue:
Selection of stationary phase particle geometry using X-ray computed tomography and Computational Fluid Dynamics simulations
04 January 2012, 01:14:55
Publication year: 2012
Source: Journal of Chromatography A, Available online 3 January 2012
Irma Schmidt, Mirjana Minceva, Wolfgang Arlt
The X-ray computed tomography (CT) is used to determine local parameters related to the column packing homogeneity and hydrodynamics in columns packed with spherically and irregularly shaped particles of same size. The results showed that the variation of porosity and axial dispersion coefficient along the column axis is insignificant, compared to their radial distribution. The methodology of using the data attained by CT measurements to perform a CFD simulation of a batch separation of model binary mixtures, with different concentration and separation factors is demonstrated. The results of the CFD simulation study show that columns packed with spherically shaped particles provide higher yield in comparison to columns packed with irregularly shaped particles only below a certain value of the separation factor. The presented methodology can be used for selecting a suited packing material for a particular separation task.
Source: Journal of Chromatography A, Available online 3 January 2012
Irma Schmidt, Mirjana Minceva, Wolfgang Arlt
The X-ray computed tomography (CT) is used to determine local parameters related to the column packing homogeneity and hydrodynamics in columns packed with spherically and irregularly shaped particles of same size. The results showed that the variation of porosity and axial dispersion coefficient along the column axis is insignificant, compared to their radial distribution. The methodology of using the data attained by CT measurements to perform a CFD simulation of a batch separation of model binary mixtures, with different concentration and separation factors is demonstrated. The results of the CFD simulation study show that columns packed with spherically shaped particles provide higher yield in comparison to columns packed with irregularly shaped particles only below a certain value of the separation factor. The presented methodology can be used for selecting a suited packing material for a particular separation task.
Highlights
► Locally distributed chromatographic parameters determined by X-Ray computed tomography. ► Axial distribution of porosity and axial dispersion insignificant compared to radial distribution. ► CFD simulation of batch separation using experimentally obtained column packing and hydrodynamics data. ► Selection of a suited stationary phase with regard to its shape by means of developed CFD model.Use of factorial design for the multivariate optimization of polypropylene membranes for the cleanup of environmental samples using the accelerated membrane-assisted cleanup approach
04 January 2012, 01:14:55
Publication year: 2012
Source: Journal of Chromatography A, Available online 3 January 2012
Tobias Schulze, René Magerl, Georg Streck, Werner Brack
Accelerated membrane-assistedcleanup (AMAC) is a recently developed method to purify extracts from matrix rich samples such as fish tissue and sediments. In this study, we tested the applicability of cast polypropylene (CPP) membranes in AMAC and evaluated the optimized dialysis procedure for the cleanup of extracts of fish tissue. Design of experiments was used to optimize the factors temperature, solvents and static time of dialysis. Main factors influencing dialysis procedure were solvents and temperature as well as the number of cycles. For the CPP membrane the optimal parameters were a temperature of 55 °C, a solvent mixture of hexane:acetone (90:10; v:v), a static time of dialysis of 6 min and 20 dialysis cycles. Comparing to the LDPE membrane this was a reduction of dialysis time from 160 to 120 min, but a higher solvent use of 150 ml per sample. However, compared to LDPE membranes CPP exhibited a lower retention of fish tissue matrix and thus reduced cleanup efficiency. Compound specific structural descriptors such as the molecular weight, the van der Waals volume and a shape factor were calculated to explain differences in diffusivity of the different model compounds. We concluded that the permeation of the molecules was related to molecular shapes and the availability of free solvent cavities in the membranes.
Source: Journal of Chromatography A, Available online 3 January 2012
Tobias Schulze, René Magerl, Georg Streck, Werner Brack
Accelerated membrane-assistedcleanup (AMAC) is a recently developed method to purify extracts from matrix rich samples such as fish tissue and sediments. In this study, we tested the applicability of cast polypropylene (CPP) membranes in AMAC and evaluated the optimized dialysis procedure for the cleanup of extracts of fish tissue. Design of experiments was used to optimize the factors temperature, solvents and static time of dialysis. Main factors influencing dialysis procedure were solvents and temperature as well as the number of cycles. For the CPP membrane the optimal parameters were a temperature of 55 °C, a solvent mixture of hexane:acetone (90:10; v:v), a static time of dialysis of 6 min and 20 dialysis cycles. Comparing to the LDPE membrane this was a reduction of dialysis time from 160 to 120 min, but a higher solvent use of 150 ml per sample. However, compared to LDPE membranes CPP exhibited a lower retention of fish tissue matrix and thus reduced cleanup efficiency. Compound specific structural descriptors such as the molecular weight, the van der Waals volume and a shape factor were calculated to explain differences in diffusivity of the different model compounds. We concluded that the permeation of the molecules was related to molecular shapes and the availability of free solvent cavities in the membranes.
Highlights
► Optimization of polymer membranes for accelerated membrane-assisted clean-up ► Significant factors are temperature and selection of solvents ► Increased recoveries of compounds using polypropylene compared to polyethylene ► Decrease in lipid removal efficacy using polypropylene membranes ► Polyethylene membranes are more suitable for AMACMeasurement of the eddy dispersion term in chromatographic columns. II. Application to new prototypes of 2.3 and 3.2 mm I.D. monolithic silica columns
04 January 2012, 01:14:55
Publication year: 2012
Source: Journal of Chromatography A, Available online 2 January 2012
Fabrice Gritti, Georges Guiochon
The mass transfer mechanisms in silica monolithic columns of the second generation was investigated, using four research samples (two 2.3 × 50 mm and two 3.2 × 50 mm silica rods) provided by their manufacturer. The heights equivalent to a theoretical plate (HETP) of these columns were measured in a range of mobile phase velocities, following a meticulous experimental protocol. The coefficients of the van Deemter equation (longitudinal diffusion term, skeleton/eluent mass transfer resistance termCuS, and eddy diffusion termA) were determined. The protocol includes using the peak parking method (to determine the longitudinal diffusion term), an accurate model of effective diffusion in silica monolithic structures (to determine the skeleton/eluent mass transfer resistance term), and an accurate method to measure the column HETP and determine the eddy diffusion term.The results show that the minimum plate heights of these new monolithic columns ranges between 4 and 5μm, three to four times lower than those observed for monolithic columns of the first generation. A detailed analysis of the eddy diffusion term demonstrates that this improvement in column efficiency is partly explained by the reduction of the domain size (the sum of the skeleton and throughpore sizes, -40%) but mostly by an increase of the radial homogeneity of the monolithic rods. The columns of this second generation exhibit residual trans-column relative velocity biases as low a 1.4% (instead of 3% for previous columns), a value which is comparable to those observed in 4.6 mm I.D. columns packed with sub-3μm core-shell particles, with which they might become competitive.
Source: Journal of Chromatography A, Available online 2 January 2012
Fabrice Gritti, Georges Guiochon
The mass transfer mechanisms in silica monolithic columns of the second generation was investigated, using four research samples (two 2.3 × 50 mm and two 3.2 × 50 mm silica rods) provided by their manufacturer. The heights equivalent to a theoretical plate (HETP) of these columns were measured in a range of mobile phase velocities, following a meticulous experimental protocol. The coefficients of the van Deemter equation (longitudinal diffusion term, skeleton/eluent mass transfer resistance termCuS, and eddy diffusion termA) were determined. The protocol includes using the peak parking method (to determine the longitudinal diffusion term), an accurate model of effective diffusion in silica monolithic structures (to determine the skeleton/eluent mass transfer resistance term), and an accurate method to measure the column HETP and determine the eddy diffusion term.The results show that the minimum plate heights of these new monolithic columns ranges between 4 and 5μm, three to four times lower than those observed for monolithic columns of the first generation. A detailed analysis of the eddy diffusion term demonstrates that this improvement in column efficiency is partly explained by the reduction of the domain size (the sum of the skeleton and throughpore sizes, -40%) but mostly by an increase of the radial homogeneity of the monolithic rods. The columns of this second generation exhibit residual trans-column relative velocity biases as low a 1.4% (instead of 3% for previous columns), a value which is comparable to those observed in 4.6 mm I.D. columns packed with sub-3μm core-shell particles, with which they might become competitive.
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