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Selected papers from the latest issue:
Separation of a binary mixture by sequential centrifugal partition chromatography
12 January 2012, 22:55:23
Publication year: 2012
Source: Journal of Chromatography A, Available online 12 January 2012
Elisabeth Hopmann, Mirjana Minceva
Sequential centrifugal partition chromatography (sCPC) is a novel continuous cyclic liquid-liquid chromatographic separation technology. Each cycle of the process comprises two steps, which differ by the liquid phase used as mobile phase (upper or lower phase) and its flow direction. The feed is introduced continuously in the unit and two product streams are collected alternately, in each step of the cycle.In this work, the sCPC was modeled using the stage (cell) model. The model was used to simulate a separation of a model binary mixture consisting of pyrocatechol and hydroquinone. The solutes distribution constants, system hydrodynamics and mass transfer parameters were determined experimentally and implemented in the model. Furthermore, a parameter study (variation of the feed concentration and step times) was performed by experiments and simulation. A recently developed method was used to select the operating parameters of the sCPC unit.
Source: Journal of Chromatography A, Available online 12 January 2012
Elisabeth Hopmann, Mirjana Minceva
Sequential centrifugal partition chromatography (sCPC) is a novel continuous cyclic liquid-liquid chromatographic separation technology. Each cycle of the process comprises two steps, which differ by the liquid phase used as mobile phase (upper or lower phase) and its flow direction. The feed is introduced continuously in the unit and two product streams are collected alternately, in each step of the cycle.In this work, the sCPC was modeled using the stage (cell) model. The model was used to simulate a separation of a model binary mixture consisting of pyrocatechol and hydroquinone. The solutes distribution constants, system hydrodynamics and mass transfer parameters were determined experimentally and implemented in the model. Furthermore, a parameter study (variation of the feed concentration and step times) was performed by experiments and simulation. A recently developed method was used to select the operating parameters of the sCPC unit.
Highlights
► Separation of binary feed mixture in a sequential centrifugal partition chromatographic (sCPC) unit is simulated using the cell model. ► The model parameters (component's distribution constants and number of cells) are determined experimentally. ► The model was validated experimentally. ► The model is suitable for simulation of sCPC separations.Unexpected retention behavior of supercritical fluid chromatography at the low density near critical region of carbon dioxide
12 January 2012, 22:55:23
Publication year: 2012
Source: Journal of Chromatography A, Available online 12 January 2012
Abhijit Tarafder, Georges Guiochon
The retention factors of octylbenzene, octadecene, anthracene, and pyrene eluted from columns packed with neat silica and C18-bonded silica by pure carbon dioxide near its critical region increase with increasing temperature along low-density isopycnic lines. This behavior is markedly different from the one observed in nearby regions of the pressure-temperature diagram of CO2, where the retention factors of these compounds decrease with increasing temperature along high-density isopycnic lines. Several possible reasons that could explain this reversal in the behavior of the retention factors are discussed. The most plausible is related to the formation of multilayer adsorption of CO2on the stationary phases in a density range slightly lower than the critical density.
Source: Journal of Chromatography A, Available online 12 January 2012
Abhijit Tarafder, Georges Guiochon
The retention factors of octylbenzene, octadecene, anthracene, and pyrene eluted from columns packed with neat silica and C18-bonded silica by pure carbon dioxide near its critical region increase with increasing temperature along low-density isopycnic lines. This behavior is markedly different from the one observed in nearby regions of the pressure-temperature diagram of CO2, where the retention factors of these compounds decrease with increasing temperature along high-density isopycnic lines. Several possible reasons that could explain this reversal in the behavior of the retention factors are discussed. The most plausible is related to the formation of multilayer adsorption of CO2on the stationary phases in a density range slightly lower than the critical density.
Highlights
► We measured retention factors along isopycnic lines ► At densities remote from critical density, they decrease with increasing temperature ► At densities close to critical density, they increase ► This can be explained by strong adsorption of CO2onto stationary phase surface.Gel-Free Shotgun Proteomic Analysis of Human Milk
12 January 2012, 22:55:23
Publication year: 2012
Source: Journal of Chromatography A, Available online 11 January 2012
Gianluca Picariello, Pasquale Ferranti, Gianfranco Mamone, Iveta Klouckova, Yehia Mechref, ...
The composition of milk has adapted during the evolution of the species to fulfill the specific nutritional needs of the offspring. Currently, it is widely recognized that milk benefits go beyond mere nutrition and serve as a source of a number of functional components to the newborn, particularly host defense effectors. However, the human milk proteome description is still incomplete, primarily because the detection of low-abundance proteins remains challenging.To overcome the limitations of the classical electrophoresis-based approach, previously separated milk fat globule membrane (MFGM) and whey protein fractions were analyzed by nanoflow-high performance liquid chromatography (HPLC)/Fourier Transform-Ion Cyclotron Resonance (FT-ICR) mass spectrometry (MS). This shotgun strategy showed an as yet unmatched potential to profile low-abundance proteins in human milk. Proteins associated with 301 different gene products were identified, some of which could be clustered into subsets of protein isoforms, thus providing one of the largest protein inventories of human milk. The identified proteins, which were derived from multiple metabolic pathways, are involved in different physiological functions, such as membrane trafficking, cell signaling, fat metabolism and transport, metabolite delivery, protein synthesis/proteolysis or folding, and immunity-related actions. Nevertheless, it appears clear from this study that the overall picture of the human milk proteome is still incomplete, although several protein signatures of milk evolution are emerging.
Source: Journal of Chromatography A, Available online 11 January 2012
Gianluca Picariello, Pasquale Ferranti, Gianfranco Mamone, Iveta Klouckova, Yehia Mechref, ...
The composition of milk has adapted during the evolution of the species to fulfill the specific nutritional needs of the offspring. Currently, it is widely recognized that milk benefits go beyond mere nutrition and serve as a source of a number of functional components to the newborn, particularly host defense effectors. However, the human milk proteome description is still incomplete, primarily because the detection of low-abundance proteins remains challenging.To overcome the limitations of the classical electrophoresis-based approach, previously separated milk fat globule membrane (MFGM) and whey protein fractions were analyzed by nanoflow-high performance liquid chromatography (HPLC)/Fourier Transform-Ion Cyclotron Resonance (FT-ICR) mass spectrometry (MS). This shotgun strategy showed an as yet unmatched potential to profile low-abundance proteins in human milk. Proteins associated with 301 different gene products were identified, some of which could be clustered into subsets of protein isoforms, thus providing one of the largest protein inventories of human milk. The identified proteins, which were derived from multiple metabolic pathways, are involved in different physiological functions, such as membrane trafficking, cell signaling, fat metabolism and transport, metabolite delivery, protein synthesis/proteolysis or folding, and immunity-related actions. Nevertheless, it appears clear from this study that the overall picture of the human milk proteome is still incomplete, although several protein signatures of milk evolution are emerging.
Highlights
► HIGHLIGHTS ► A shotgun approach enabled the identification of 301 proteins in human milk. ► Several novel low-abundance, physiological relevant gene products were identified. ► Proteins involved in delivering lipids were unexpectedly numerous. ► The proteome of human milk still awaits to be completed.New insights in the velocity dependency of the external mass transfer coefficient in 2D and 3D porous media for liquid chromatography
12 January 2012, 22:55:23
Publication year: 2012
Source: Journal of Chromatography A, Available online 11 January 2012
Sander Deridder, Gert Desmet
Numerical calculations of the mobile zone mass transfer rate in a variety of ordered 2D and 3D structures are presented. These calculations are in line with earlier theoretical and experimental findings made in the field of chemical engineering and suggest that the Sherwood-number (Shm) appearing in the mobile phase mass transfer term of the general plate height expression of liquid chromatography is not correctly predicted by the Wilson-Geankoplis- or the Kataoka- or the penetration model expression that have been used up to now to in the field of LC, and that at least more research is needed before these expressions can be continued to be used with confidence. The aforementioned expressions were obtained by neglecting the effect of axial dispersion on the mass transfer process, and it seems that they therefore underestimate the true Shm-number by a factor of 2 to 5 around the minimum of the van Deemter-curve. New correlations describing the variation of the Shm-coefficient as a function of the reduced velocity for a number of other packing geometries (tetrahedral monolith, 2-D pillar array) are proposed. These correlations are in agreement with earlier theoretical and experimental studies showing that at low velocities the local-driving force-based Shm-value is of the order of 10 to 20 in a packed bed column with an external porosity on the order of 35 to 40%.
Source: Journal of Chromatography A, Available online 11 January 2012
Sander Deridder, Gert Desmet
Numerical calculations of the mobile zone mass transfer rate in a variety of ordered 2D and 3D structures are presented. These calculations are in line with earlier theoretical and experimental findings made in the field of chemical engineering and suggest that the Sherwood-number (Shm) appearing in the mobile phase mass transfer term of the general plate height expression of liquid chromatography is not correctly predicted by the Wilson-Geankoplis- or the Kataoka- or the penetration model expression that have been used up to now to in the field of LC, and that at least more research is needed before these expressions can be continued to be used with confidence. The aforementioned expressions were obtained by neglecting the effect of axial dispersion on the mass transfer process, and it seems that they therefore underestimate the true Shm-number by a factor of 2 to 5 around the minimum of the van Deemter-curve. New correlations describing the variation of the Shm-coefficient as a function of the reduced velocity for a number of other packing geometries (tetrahedral monolith, 2-D pillar array) are proposed. These correlations are in agreement with earlier theoretical and experimental studies showing that at low velocities the local-driving force-based Shm-value is of the order of 10 to 20 in a packed bed column with an external porosity on the order of 35 to 40%.
Highlights
► Numerical calculations of the Sherwood number in ordered beds have been made ► Results suggest that validity of Wilson-Geankoplis expression may need revisal ► Results are in agreement with earlier studies in the field of chemical engineering ► New correlations improve fitting quality of the general rate expressionDevelopment of a carbon clad core shell silica for high speed two-dimensional liquid chromatography
12 January 2012, 22:55:23
Publication year: 2012
Source: Journal of Chromatography A, Available online 11 January 2012
Changyub Paek, Yuan Huang, Marcelo Filgueira, Alon V. McCormick, Peter W. Carr
We recently introduced a new method () to deposit carbon on fully porous silicas (5 μm) to address some of the shortcomings of carbon clad zirconia (C/ZrO2), which has rather low retention due to its low surface area (20–30 m/g). The method enables the introduction of a thin, homogeneous layer of Al (III) on silica to serve as catalytic sites for carbon deposition without damaging the silica's native pore structure. Subsequent carbon deposition by chemical vapor deposition resulted in chromatographically useful carbon phases as shown by good efficiencies and higher retentivity relative to C/ZrO2.Herein, we use the above method to develop a novel carbon phase on superficially porous silica (2.7 μm). This small, new form of silica offers better mass transfer properties and higher efficiency with lower column back pressures as compared to sub 2 μm silica packings, which should make it attractive for use as the second dimension in fast two-dimensional LC (LC x LC). After carbon deposition, several studies were conducted to compare the new packing with C/ZrO2. Consistent with work on 5 μm fully porous silica, the metal cladding did not cause pore blockage. Subsequent carbon deposition maintained the good mass transfer properties as shown by the effect of velocity on HETP. The new packing exhibits efficiencies up to ∼ 5.6 fold higher than C/ZrO2for polar compounds. We observed similar chromatographic selectivity for all carbon phases tested. Consequently, the use of the new packing as the second dimension in fast LC x LC improved the peak capacity of fast LC x LC. The new material gave loading capacities similar to C/ZrO2, which is rather expected based on the surface areas of the two phases.
Source: Journal of Chromatography A, Available online 11 January 2012
Changyub Paek, Yuan Huang, Marcelo Filgueira, Alon V. McCormick, Peter W. Carr
We recently introduced a new method () to deposit carbon on fully porous silicas (5 μm) to address some of the shortcomings of carbon clad zirconia (C/ZrO2), which has rather low retention due to its low surface area (20–30 m/g). The method enables the introduction of a thin, homogeneous layer of Al (III) on silica to serve as catalytic sites for carbon deposition without damaging the silica's native pore structure. Subsequent carbon deposition by chemical vapor deposition resulted in chromatographically useful carbon phases as shown by good efficiencies and higher retentivity relative to C/ZrO2.Herein, we use the above method to develop a novel carbon phase on superficially porous silica (2.7 μm). This small, new form of silica offers better mass transfer properties and higher efficiency with lower column back pressures as compared to sub 2 μm silica packings, which should make it attractive for use as the second dimension in fast two-dimensional LC (LC x LC). After carbon deposition, several studies were conducted to compare the new packing with C/ZrO2. Consistent with work on 5 μm fully porous silica, the metal cladding did not cause pore blockage. Subsequent carbon deposition maintained the good mass transfer properties as shown by the effect of velocity on HETP. The new packing exhibits efficiencies up to ∼ 5.6 fold higher than C/ZrO2for polar compounds. We observed similar chromatographic selectivity for all carbon phases tested. Consequently, the use of the new packing as the second dimension in fast LC x LC improved the peak capacity of fast LC x LC. The new material gave loading capacities similar to C/ZrO2, which is rather expected based on the surface areas of the two phases.
Highlights
► We developed a carbon stationary phase coated on superficially porous silica (2.7 μm). ► The new packing provides the unique chromatographic selectivity of carbon stationary phases. ► This packing shows efficiency up to ∼ 5.6 fold higher than carbon clad zirconia for polar compounds. ► The use of the new packing as the 2dimension in fast LC x LC improved the peak capacity of fast LC x LC.Simultaneous Determination of Mono- and Disubstituted Polyfluoroalkyl Phosphates in Drinking Water by Liquid Chromatography-Electrospray Tandem Mass Spectrometry
12 January 2012, 22:55:23
Publication year: 2012
Source: Journal of Chromatography A, Available online 11 January 2012
Huanhuan Ding, Hui Peng, Min Yang, Jianying Hu
A sensitive liquid chromatography-electrospray tandem mass spectrometry method was established for the simultaneous determination of five monosubstituted polyfluoroalkyl phosphates (monoPAPs) and eight disubstituted polyfluoroalkyl phosphates (diPAPs) in drinking water. Complete separation and good retention for 13 polyfluoroalkys phosphates (PAPs) were achieved with a Waters ACUITY UPLC BEH C8 column using a mixture of methanol/water containing 0.1% NH4OH as the mobile phases. Extraction of drinking water samples was performed on weak anion exchange (WAX) cartridges, and the recoveries of target compounds were from 65 to 110%. The limits of quantization (LOQs) for 13 analytes were in the range of 0.4-40 ng/L. This method was applied to analyze the PAPs in drinking water samples from three cities in China. Of the 13 PAPs, six PAPs including 6:2 monoPAP (13.0 ng/L), 8:2 monoPAP (3.6 ng/L), 10:1 monoPAP (4.3-70.3 ng/L), 10:2 monoPAP (1.4-5.6 ng/L), 8:2 diPAP (0.10 ng/L), and 10:1 diPAP (0.8-3.8 ng/L) were detected.
Source: Journal of Chromatography A, Available online 11 January 2012
Huanhuan Ding, Hui Peng, Min Yang, Jianying Hu
A sensitive liquid chromatography-electrospray tandem mass spectrometry method was established for the simultaneous determination of five monosubstituted polyfluoroalkyl phosphates (monoPAPs) and eight disubstituted polyfluoroalkyl phosphates (diPAPs) in drinking water. Complete separation and good retention for 13 polyfluoroalkys phosphates (PAPs) were achieved with a Waters ACUITY UPLC BEH C8 column using a mixture of methanol/water containing 0.1% NH4OH as the mobile phases. Extraction of drinking water samples was performed on weak anion exchange (WAX) cartridges, and the recoveries of target compounds were from 65 to 110%. The limits of quantization (LOQs) for 13 analytes were in the range of 0.4-40 ng/L. This method was applied to analyze the PAPs in drinking water samples from three cities in China. Of the 13 PAPs, six PAPs including 6:2 monoPAP (13.0 ng/L), 8:2 monoPAP (3.6 ng/L), 10:1 monoPAP (4.3-70.3 ng/L), 10:2 monoPAP (1.4-5.6 ng/L), 8:2 diPAP (0.10 ng/L), and 10:1 diPAP (0.8-3.8 ng/L) were detected.
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