Column Inlet Research Articles

Transport of Giardia and Manure Suspensions in Saturated Porous Media

Experiments were conducted to elucidate the transport behavior of cysts of Giardia and manure suspensions through several aquifer sands. Decreasing the median grain size of the sand resulted in lower peak effluent concentrations and increased deposition of the Giardia and manure particles in the sand near the column inlet. The effluent concentration curves for the manure suspensions also exhibited asymmetric shapes that tended to include larger particle sizes as the manure suspension was continuously added. Simulations of the transport of Giardia and manure particles using a simple and flexible power law model for the solid-water mass exchange term provided a satisfactory description of the effluent and spatial distribution data. The cumulative size distribution (CSD) of manure particles in the suspension initially and after passage through the packed columns was used to identify the mechanisms that were controlling the deposition of manure particles and Giardia. The CSD data indicated that manure particles were completely removed at early times by mechanical filtration and/or straining when the ratio of the particle to the median grain diameter was greater than 0.003 to 0.017. However, the CSD changed with increasing time due to deposition-induced filling of straining sites. The Giardia transport was controlled by straining. For a given sand, higher effluent concentrations of Giardia were observed in the presence than in the absence of manure suspension. The relative increase of Giardia in the effluent concentrations varied from 75 to 172%. Hence, pathogen transport studies conducted in the absence of manure suspension may underestimate transport potential in manure-contaminated environments.

Concentration dependent transport of colloids in saturated porous media

A series of column experiments was undertaken to explore the influence of colloid input concentration (2, 1, 0.5, and 0.25 times a reference concentration), colloid size (negatively charged 3.2 and 1.0 μm carboxyl latex), and sand grain size (360, 240, and 150 μm quartz sands) on transport and deposition. A similar mass of stable mono-dispersed colloids was added to each column. For a given input concentration, decreasing the sand size and increasing the colloid size resulted in increased mass retention in the sand near the column inlet and lower relative concentrations in the effluent. For a given sand and colloid, increasing the input concentration produced less deposition and higher mass recovery in the effluent, especially for coarser sands and smaller colloids. Results of a time dependent attachment (blocking) and detachment model were not consistent with this behavior because the simulations predicted much less retention near the column inlet and a decreasing number of favorable attachment sites (mass of deposited colloids) with increasing input concentration in a given system (colloid and sand). A time dependent straining model (filling of straining sites) provided a better description of the effluent and deposition data, but still could not account for the observed concentration dependent mass recovery. Alternatively, the straining model was refined to include a liberation term that assumed that straining was hindered at higher concentrations (collision frequencies) due to repulsive colloid (aqueous phase)–colloid (strained) interactions. Simulations that included straining, liberation, attachment, and detachment significantly improved the description of the experimental data.

Development of dual gradient column in liquid chromatography

The dual gradient column, in which both the chemical property of the stationary phase and the flow velocity in the mobile phase are heterogeneous longitudinally along the column, is developed to obtain the mobile phase gradient-like elution in an isocratic condition. Here, the step-wise dual gradient columns were prepared by connecting an inlet column (I.D. 50 μm, packed with ODS) serially to an outlet column (I.D. 100–200 μm, packed with the mixture of ODS and C1 [9:1]). The retention behavior of alkylbenzenes was able to be controlled in the dual gradient column depending on the variation in the flow velocity. Moreover, the change in retention behavior induced by the flow velocity variation for the dual gradient columns was quite different from that by the variation in organic modifier content of the mobile phase in isocratic elution for a single gradient column and can induce the similar effect with an ordinary gradient elution in a mobile phase composition.

Negative mode sheathless capillary electrophoresis electrospray ionization-mass spectrometry for metabolite analysis of prokaryotes

Capillary electrophoresis (CE) was coupled to negative mode electrospray ionisation-mass spectrometry (MS) for separation and detection of phosphorylated and acidic metabolites in extracts of prokaryotes. Unlike previous CE–MS systems for metabolite analysis, a sheathless interface was used to improve sensitivity. To accomplish this, the separation capillary was modified by creating a porous junction near the outlet where the electrospray voltage and cathodic voltage for CE were applied. The outlet of the capillary was pulled to a 5 μm inner diameter to form an electrospray emitter and had a frit fabricated near the exit to prevent clogging. During analysis pressure was applied at the inlet of the separation column to create sufficient flow towards the detector. Limits of detection for 19 metabolites in full scan mode ranged from 20 nM for ADP ribose to 2.5 μM for α-ketoglutarate for 40 nL injections. Extracts of Escherichia coli, strain DH5-α, were analyzed using this system. In full scan mode, 118 different metabolites were detected. Tandem mass spectrometry was also employed to attempt identification. Reproducible fragmentation of 19 parent peaks was found and 10 of these produced spectra that were consistent with identification obtained from matching to compounds in the MetaCyc database. These results demonstrate the utility of a sensitive CE–MS system for large scale metabolite detection in biological samples.

The Use of Ultrashort Monolithic Porous Columns and an Eluent Flow Gradient for Chromatographic Separation of Polyaromatic Hydrocarbons

An important task of state-of-the-art high performance liquid chromatography (HPLC) is to decrease the time of analysis. There exist several approaches to solving this task. The first one implies the use of short (3 − 5 cm long) columns packed with particles 1.5–3 μ m in diameter [1]. These tiny particles ensure an effective mass transfer and rather high column efficiency. Complete separation of five inorganic anions requires 2 min at a flow rate of 1 mL/min. However, the high pressure at the column inlet precludes the possibility of increasing the eluent flow rate and thus of reducing additionally the time of analysis. For separation at higher flow rates, it is necessary to raise the column temperature.

Step change of mobile phase flow rates to enhance protein folding in size exclusion chromatography

Minimal aggregation formation between injector and column inlet and enough residence time inside the column were identified to be the key for proper proteins refolding by size exclusion chromatography (SEC). Therefore, a step change of mobile phase flow rate strategy was developed. That is, during the injected denatured protein (sample) traveling from injector to column inlet, a higher rate of mobile phase should be applied to reduce aggregation. Then, a lower flow rate should be used to allow enough time for protein to refold inside the column. The refolding of denatured lysozyme in SEC by this method was shown to reduce the aggregation and thus resulting in good refolding yields, though not completely. Combining this method together with our previously proposed chaperon solvent plug strategy could obtain complete recovery of denatured protein, both mass and activity recoveries.

Gas–liquid phase distribution and void fraction measurements using MRI

We used a permanent-magnet magnetic resonance imaging (MRI) system to estimate the integral, spatially- and temporally-resolved void fraction distributions and flow patterns in vertical gas–liquid two-phase flow. Air was introduced at the bottom of the stagnant liquid column using an accurate and programmable syringe pump. The air flow rate was in upward vertical direction against the gravity vector. Air flow rates were varied between 1 and 200 ml/min. Bubble formation and detachment at the inlet of the vertical column was non-uniform. The cylindrical non-conducting test tube in which two-phase flow is characterized was placed in a 0.26 T permanent-magnet MRI unit. A roughly linear relationship has been observed for the integral void fraction versus volume flow rate of air through vertical stagnant liquid column. Integral or sample-averaged void fraction was obtained by volume-averaging of the spatially-resolved signals. Spatial averaging was performed in a radial or longitudinal axis of the column. The time-averaged spatially-resolved void fraction has also been obtained for the quasi-steady flow of air in a stagnant liquid column. No great accuracy is claimed as this was an exploratory proof-of-concept type of experiment. Preliminary results show that MRI can indeed provide qualitative and quantitative data and is especially well suited for characterization of averaged transport processes in adiabatic and diabatic multi-phase and/or multi-component flows. Better and faster MRI sequences could improve spatial and temporal resolutions significantly.

Spatial Variation in Deposition Rate Coefficients of an Adhesion-Deficient Bacterial Strain in Quartz Sand

The transport of bacterial strain DA001 was examined in packed quartz sand under a variety of environmentally relevant ionic strength and flow conditions. Under all conditions, the retained bacterial concentrations decreased with distance from the column inlet at a rate that was faster than loglinear, indicating that the deposition rate coefficient decreased with increasing transport distance. The hyperexponential retained profile contrasted againstthe nonmonotonic retained profiles that had been previously observed for this same bacterial strain in glass bead porous media, demonstrating that the form of deviation from log-linear behavior is highly sensitive to system conditions. The deposition rate constants in quartz sand were orders of magnitude below those expected from filtration theory, even in the absence of electrostatic energy barriers. The degree of hyperexponential deviation of the retained profiles from loglinear behavior did not decrease with increasing ionic strength in quartz sand. These observations demonstrate thatthe observed low adhesion and deviation from log-linear behavior was not driven by electrostatic repulsion. Measurements of the interaction forces between DA001 cells and the silicon nitride tip of an atomic force microscope (AFM) showed that the bacterium possesses surface polymers with an average equilibrium length of 59.8 nm. AFM adhesion force measurements revealed low adhesion affinities between silicon nitride and DA001 polymers with approximately 95% of adhesion forces having magnitudes < 0.8 nN. Steric repulsion due to surface polymers was apparently responsible for the low adhesion to silicon nitride, indicating that steric interactions from extracellular polymers controlled DA001 adhesion deficiency and deviation from log-linear behavior on quartz sand.

Straining, Attachment, and Detachment of Cryptosporidium Oocysts in Saturated Porous Media

Accurate knowledge of the transport and deposition behavior for pathogenic Cryptosporidium parvum oocysts is needed to assess contamination and protect water resources. Experimental and modeling studies were undertaken to examine the roles of attachment, detachment, and straining on oocyst transport and retention. Saturated column studies were conducted using Ottawa aquifer sands (U.S. Silica, Ottawa, IL) with median grain sizes of 710, 360, and 150 microm. Decreasing the median sand size tended to produce lower effluent concentrations, greater oocyst retention in the sand near the column inlet, and breakthrough of oocysts at later times. Oocyst transport data also exhibited concentration tailing. Mathematical modeling of the oocyst transport data using fitted first-order attachment and detachment coefficients provided a satisfactory description of the observed effluent concentration curves, but a poor characterization of the oocyst spatial distribution. Modeling of these data using an irreversible straining term that is depth dependent provided a better description of the oocyst spatial distribution, but could not account for the observed effluent concentration tailing or late breakthrough times. A more physically realistic description of the data was obtained by modeling attachment, detachment, and straining. The percentage of total oocysts retained by straining was estimated from effluent mass balance considerations to be 68% for 710-microm sand, 79% for 360-microm sand, and 87% for 150-microm sand. Straining coefficients were then selected to achieve these percentages of total oocyst retention, and attachment and detachment coefficients were fitted to the effluent concentration curves. Dramatic differences in the predicted oocyst breakthrough curves were observed at greater transport distances for the various model formulations (inclusion or exclusion of straining). Justification for oocyst straining was provided by trends in the transport data, simulation results, pore size distribution information, and published literature.

Detachment-Influenced Transport of an Adhesion-Deficient Bacterial Strain within Water-Reactive Porous Media

Bacteria and carboxylate-modified microsphere transport experiments were performed in glass bead packed columns in order to examine the distribution of retained colloids on the sediment. Solution pH was allowed to vary from 6.0 to 9.4 across the length of the column (20 cm) in order to examine potential effects of solution chemistry on the retained profiles. Both the microspheres and the bacteria showed retained profiles that deviated strongly from log-linear behavior expected from a spatially invariant colloid deposition rate coefficient. Deviation for the microspheres was in the form of steeper-than-expected decreases in retained concentrations with distance from source. Deviation for the bacteria was in the form of maximum retained concentrations that were located down-gradient from the column inlet. Subsidiary experiments with varying elution times showed that detachment during elution moved the peak of mass of retained bacteria down-gradient of the column inlet; however, the disproportional translation of the peak of mass relative to elution time indicated that processes operating during injection produced the initial down-gradient translation of peak concentrations of retained cells.

Metal tubing/frit with a sintered frit of silica particles and a chromatography column with such tubing/frits

This study is about the metal tubing/frit prepared by treating a powdered silica with a strong base, drying it, scrubbing it into powders, putting it in the tip of metal tubing at a proper depth, and sintering the powders to form a durable sintered frit. This study is also about a liquid chromatographic column prepared by installing the metal tubing/frit at the column inlet and outlet unions and by placing the column main body tubing packed with a stationary phase between the two unions. The metal tubing/frit made according to the description is easily replaced and fixed without disassembling the column when it is necessary. The column of this design could be a cheap substitute for the conventional microcolumn.

Separation of Organic Compounds by Simulated Moving Bed Preparative Liquid Chromatography

In this experimental work laboratory-scale four-column equipment (L=25 cm, i.d.=1 cm) was planned and constructed, with the co-operation of the Central Mechanical Workshop, University of Veszprem, for separation of two steroid isomers [1] using YMC S-50 silica gel as adsorbent. The effect of changing the composition of fresh eluent (in this work acetone-dichloromethane) on component separation was examined—the amount of acetone in the mixture was 40, 50, 60, or 70% (v/v). Product purity and other specifications (yield, productivity, eluent consumption) were measured by gas chromatography. An equilibrium mathematical model of the SMB process for open and closed eluent cycles was constructed by means of a computer program [2, 3]. Adsorption equilibrium, and kinetic data, theoretical plate number measurement, frontal and elution adsorption–desorption measurements for determination of the optimum conditions for the SMB process and for construction of the mathematical model were measured by means of laboratory experiments. Finally, results from the simulation programme were compared with measurement results. Our conclusion on the basis of laboratory measurements was that varying the composition of fresh acetone-dichloromethane eluent between 40:60 and 60:40% (v/v) and applying 5 g L−1 steroid mixture to the column inlet enables satisfactory isolation of component B by the SMB process, although the effect of modifying model parameters will be investigated in further work.

Straining and Attachment of Colloids in Physically Heterogeneous Porous Media

Colloid transport studies were conducted in water‐saturated physically heterogeneous systems to gain insight into the processes controlling transport in natural aquifer and vadose zone (variably saturated) systems. Stable monodispersed colloids (carboxyl latex microspheres) and porous media (Ottawa quartz sands) that are negatively charged were employed in these studies. The physically heterogeneous systems consisted of various combinations of a cylindrical sand lens embedded in the center of a larger cylinder of matrix sand. Colloid migration was found to strongly depend on colloid size and physical heterogeneity. A decrease in the peak effluent concentration and an increase in the colloid mass removal in the sand near the column inlet occurred when the median grain size of the matrix sand decreased or the size of the colloid increased. These observations and numerical modeling of the transport data indicated that straining was sometimes an important mechanism of colloid retention. Experimental and simulation results suggest that attachment was more important when the colloid size was small relative to the sand pore size. Transport differences between conservative tracers and colloids were attributed to flow bypassing of finer‐textured sands, colloid retention at interfaces of soil textural contrasts, and exclusion of colloids from smaller pore spaces. Colloid retention in the heterogeneous systems was also influenced by spatial variations in the pore water velocity. Parameters in straining and attachment models were successfully optimized to the colloid transport data. The straining model typically provided a better description of the effluent and retention data than the attachment model, especially for larger colloids and finer‐textured sands. Consistent with previously reported findings, straining occurred when the ratio of the colloid and median grain diameters was &gt;0.5%.

Straining and Attachment of Colloids in Physically Heterogeneous Porous Media

Colloid transport studies were conducted in water-saturated physically heterogeneous systems to gain insight into the processes controlling transport in natural aquifer and vadose zone (variably saturated) systems. Stable monodispersed colloids (carboxyl latex microspheres) and porous media (Ottawa quartz sands) that are negatively charged were employed in these studies. The physically heterogeneous systems consisted of various combinations of a cylindrical sand lens embedded in the center of a larger cylinder of matrix sand. Colloid migration was found to strongly depend on colloid size and physical heterogeneity. A decrease in the peak effluent concentration and an increase in the colloid mass removal in the sand near the column inlet occurred when the median grain size of the matrix sand decreased or the size of the colloid increased. These observations and numerical modeling of the transport data indicated that straining was sometimes an important mechanism of colloid retention. Experimental and simulation results suggest that attachment was more important when the colloid size was small relative to the sand pore size. Transport differences between conservative tracers and colloids were attributed to flow bypassing of finer-textured sands, colloid retention at interfaces of soil textural contrasts, and exclusion of colloids from smaller pore spaces. Colloid retention in the heterogeneous systems was also influenced by spatial variations in the pore water velocity. Parameters in straining and attachment models were successfully optimized to the colloid transport data. The straining model typically provided a better description of the effluent and retention data than the attachment model, especially for larger colloids and finer-textured sands. Consistent with previously reported findings, straining occurred when the ratio of the colloid and median grain diameters was >0.5%.

Evaluation and prediction of the shape of gas chromatographic peaks

The evaluation and prediction of the shape of asymmetric gas chromatographic peaks is important as the knowledge of the amount of tailing permits to foresee the resolution between closely eluting peaks and to select the best analytical conditions for an efficient and rapid separation. A model function was tested in order to approximate the true peak shape obtained on non-polar column by injecting different compounds. The trend of the parameters involved in the used equation has been investigated as a function of column temperature and inlet pressure. The reproduction of the symmetrical or asymmetrical shape of gas chromatographic peaks is satisfactory and the method also permits to predict the shape of peaks obtained in different conditions of temperature and pressure.

Evaluation of the uniformity of analytical-size chromatography columns prepared by the downward packing of particulate slurries.

The axial heterogeneity of downward slurry-packed chromatography columns was evaluated. A series of columns were prepared that varied in total length from 5 to 30 cm. Each column was packed in stainless steel tubing that was sectioned to allow the column to be divided into 5-cm sections after packing. Each 5-cm section of these columns was then tested for chromatographic performance. In total, 22 such column sections were tested. The results of the study show that the consolidation of the packed bed is a very complex problem, yet systematic variations of the column performance were observed, depending on the location of the section tested from within the entire column. For example, when columns longer than 20 cm were packed, the most homogeneous and best performing section of the column was the lower midsection. Whereas for columns shorter than 20 cm in length, the best sectioned region of the bed was the lower and outlet region. In all cases, the most poorly packed region of the bed was the column inlet section, irrespective of the bed length. The phenomenon associated with this axial heterogeneity undoubtedly results from a complex interplay between wall friction, particle momentum, and the pressure pulsations resulting from the packing process.

A laboratory study of landfill-leachate transport in soils

Continuous flow experiments were conducted using sand-packed columns to investigate the relative significance of bacterial growth, metal precipitation, and anaerobic gas formation on biologically induced clogging of soils. Natural leachate from a local municipal landfill, amended with acetic acid, was fed to two sand-packed columns operated in upflow mode. Degradation of the influent acetic acid resulted in the production of methane and carbon dioxide, and simultaneous reduction of manganese, iron, and sulphate. Subsequent increase in the influent acetic acid concentration from 1750 to 2900 mg/l, and then to 5100 mg/l, led to rapid increase in the dissolved inorganic carbon, solution pH, and soil-attached biomass concentration at the column inlet, which promoted the precipitation of Mn 2+ and Ca 2+ as carbonate, and Fe 2+ as sulphide. An influent acetic acid concentration of 1750 mg/l decreased the soil's hydraulic conductivity from an initial value of 8.8×10 −3 cm/s to approximately 7×10 −5 cm/s in the 2–6 cm section of the column. Increasing the influent acetic acid to 5100 mg/l only further decreased the hydraulic conductivity to 3.6×10 −5 cm/s; rather, the primary effect was to increase the length of the zone experiencing reduced hydraulic conductivity from 0–6 cm to the entire column. As bioaccumulation was limited to the 0–5 cm section of the column, and the effect of metal precipitation was negligible, the reduction on the deeper sections of the column is attributed to gas flow, which was up to 1440 ml/day. Mathematical modelling shows that biomass accumulation and gas formation were equally significant in reducing the hydraulic conductivity, while metal precipitation contributed only up to 4% of the observed reduction.

Inability of unpacked gooseneck liners to stop the sample liquid after injection with band formation (fast autosampler) into hot GC injectors.

With the introduction of the fast autosampler, the rules on how to perform splitless injection should have been revisited: the fast autosampler releases the sample liquid as a band that is no longer nebulized by solvent vapors as in previous injection techniques. In empty gooseneck liners, the sample liquid is shot to the bottom of the injector and jumps around in a largely uncontrolled manner. Visual experiments showed that the liquid is partially rejected. Another portion passes by the column inlet into the column attachment region, while the last part may directly enter the column. The impact on chromatography was investigated by using a mixture of n-alkanes: the higher boiling components passing by the column entrance into the zone of the column attachment were largely lost, i.e., were discriminated against the volatile components. It was concluded that empty gooseneck liners are not suitable for injection by fast autosamplers.

Evaluation of packed capillary liquid chromatography columns and comparison with conventional-size columns

Apart from extracolumn effects peak dispersion in liquid chromatographic columns is caused by the column inlet, the packed bed, and the column outlet. A strategy applicable for independent evaluation of the individual sources of column band broadening was developed on the basis of the linear extrapolation method (LEM). This method was applied to compare the performance of packed capillary LC columns from various commercial suppliers with conventional-size columns. The columns differed widely in their performance with respect to peak shapes and widths for standard substances. The capillary columns were found well packed, but in some cases overall performance would benefit from improving the design of the area between the packed bed and the connecting capillaries, containing frits as well as dead volumes.

Systematic Study of Feed Temperature Control to High Performance Liquid Chromatography

Some system factors like poor packing, distribution system and viscous heat dissipation may result in the core of a solute concentration band goes faster, forming a parabolic concentration band and reducing column efficiency. Feed temperature control method, which is to appropriately control eluent at the column inlet at a temperature lower than the wall temperature, can modify the band shape and counteract such negative effects. Using Computational Fluid Dynamics (CFD) software FLUENT, the present work investigated the effect of a variety of system factors on the temperature distribution in a chromatographic column and the optimal temperature difference between the inlet and the column wall in feed temperature control, ΔTopt. It was found that the factors affecting flow distribution have no significant effect on temperature distribution but significantly affect ΔTopt. The factors strongly related to temperature distribution might not interfere with ΔTopt. The reason is that the principle of feed temperature control is to reshape the solute concentration band, which depends on flow distribution. This work also found that for a given column and a given eluent, ΔTopt was independent of the Reynolds No and Peclet No derived from component balance ΔTopt depends on Peclet No derived from energy balance, but the correlation between them is uncertain due to the unclear effect of λeff on ΔTopt.