Column Inlet Research Articles

Reviews on recent trends in chromatography/mass spectrometry coupling. Part IV. Reasons why supercritical fluid chromatography is not so easily coupled with mass spectrometry as originally assessed

When SFC was rediscovered in the early 1980s, it was frequently estimated that a strong driving force to its development would be the ease of devising a simple SFC/MS interface. This was believed to be easily achieved if analytical conditions were limited to capillary SFC columns as a general separation tool, and to the choice of neat CO2 as the unique supercritical fluid. The low flow rate of mobile phase delivered by capillary columns was easy to accommodate by the vacuum equipment of standard mass spectrometers, and the specific physical properties of CO2 made possible solute ionization by different ion-molecule reactions, especially charge exchange ionization. This approach has lived up to all of its promises. The major causes of the observed mismatch are the large variations of the MS source pressure as a result of the CO2 pressure gradient at the SFC column inlet, the low sensitivity of charge exchange ionization at these high MS source pressures, and the inability to handle polar and nonvolatile molecules. Adaptation of LC/MS interfaces, such as the thermospray interface or the particle beam interface, to SFC/MS conditions was a step forward, but these devices have their own limitations. Alternative methods to direct SFC/MS coupling have been investigated recently. They are based on the use of packed columns rather than capillaries, and on solute ionization at atmospheric pressure rather than under a vacuum, by means of either gas-phase corona discharge ionization or liquidphase electrospray ionization. These new developments may revive research into the design of reproducible and sensitive SFC/MS systems where the number of recent studies is still low compared with other chromatography/mass spectrometry coupling studies.

Pilot Plant Studies on Filtration of Raw Sewage Using Floating Filter Media and Multiple Filter Column Inlets

The characteristics and performance of solid-liquid separation of raw sewage using floating media and multiple inlets were studied using pilot-scale equipment. Particles over 7 µm, representing approximately 80% of SS and 50% of BOD in raw sewage were efficiently removed. Smaller particles and soluble components, comprising a large part of total BOD, were difficult to remove by filtration. The maximum SS removal ratio (SSRR) and SS quantity removed per unit filter surface (SSR) was achieved using a medium size of 5.5 mm and a filtration rate of 150 µm/d. Inlet switching to a lower position significantly extended the filter run lengths and increased the total SS removed by filtration. Using 5.5 mm filter particles and a 150 m/d filtration rate, 80-89% of SS was removed, 38-42 kg of SS was removed per unit filter sectional area, and filter runs were 55-65 hours. The backwash-filtrate ratio was around 2%. The space requirement of this system will be significantly smaller than the ordinary primary treatment system judging from the trial design of a prototype plant.

Large-volume injection in capillary supercritical fluid chromatography

A system was developed to introduce large sample volumes (100 μL or more) into a capillary supercritical fluid chromatograph (SFC). Capillary columns of 50-μm internal diameter (l.d.) were used without a noticeable decrease in chromatography efficiency and resolution. The sample introduction system consisted of a series of valves which were operated to effect sampling into an inlet column, followed by a solvent elimination step

Clinical and immunologic effects of Staphylococcal protein A immunoadsorption therapy for inhibitor to factor VIII

A 74-year mild hemophiliac with an inhibitor to factor VIII underwent five 2-L plasma immunoadsorption procedures with a Staphylococcal protein A (Prosorba) column over 7 days. Initially, the inhibitor level increased from 56 to 154 BU/mL. Serum immunoglobulins, immune complexes, C3 and C4 fell progressively with each procedure: C3a was increased. Before therapy, the patient had increased cytotoxic T and activated T cells which decreased to the normal range with treatment. The proportion of T inducer cell and CD4:CD3 ratios increased progressively with each treatment. Natural killer cell activity remained unchanged. Unstimulated patient lymphocytes showed high proliferative activity, but after therapy there was markedly reduced response to mitogens. Both patient and normal lymphocytes showed marked increase in thymidine incorporation when incubated with adsorbed plasma (from column outlet), compared to incubation with unadsorbed plasma (column inlet). The patient's serum showed a progressive rise in this “mitogenicity” effect, maximal after the third procedure, then declining to pre-treatment levels after the fifth procedure. After the third immunoadsorption, inhibitor level was 70 BU/mL and he was given prednisone and cyclophosphamide; after the fifth procedure it was 32 BU/mL and 6 months later was undetectable. Although subsequent decrease in the inhibitor may have been due to the plasma immunoadsorption, it is important to note that this treatment may be paradoxically associated with a rise in antibody levels. In addition to antibody changes, Staph. protein A perfusion affected cellular immunity.

Effect of modulator sorption in gradient elution chromatography: gradient deformation

In gradient elution chromatography, the mobile phase composition at the column inlet is a function of time. The consequences of accounting for the adsorption of the mobile phase components themselves are investigated for the experimentally common situation of a linear inlet gradient. Surface excess adsorption data from the literature for water-acetonitrile mobile phases in reversed-phase chromatography using different octadecyl stationary phases are shown to be in good internal agreement. The resulting individual isotherms as calculated by Tani and Suzuki (1989) are fitted to Langmuir and BET forms; it is shown that the Langmuirian form fits the data well except at extremely high acetonitrile concentrations. Using these isotherm parameters, it is found that a linear inlet gradient could suffer significant distortion while moving down the column. In the extreme case, a shock front of the mobile phase modulator could result. Analytical expressions are derived describing the conditions under which such a shock could occur within the column and its subsequent path, assuming Langmuirian sorption.

GCSIM: A gas-liquid chromatography simulator for educational purposes

A gas-liquid chromatography simulation program was written for personal computers. A graphic display of a chromatogram is shown by the simulator. The program can be used to illustrate various effects in gas chromatography for demonstrations or lectures. In addition, it can be used as an advanced supplemental instrument simulator in a practical course. Variables include column length, inlet pressure, phase ratio, temperature (both isothermal and linear programming) and detector attenuation. Additional parameters offer a choice between packed and capillary columns, two different detectors, two stationary phases and two carrier gases. The sample composition can be changed to include any solvent and up to six components from a library of 75 at different concentrations.

Effects of electron acceptors on halogenated organic compound biotransformations in a biofilm column

The transformability of trihalomethanes, carbon tetrachloride, 1,1,1-trichlorethane, 1,2-dibromomethane, tetrachlorethylene, dibromochloropropane, and chlorinated benzenes was evaluated by a biofilm utilizing a mixture of primary electron acceptors (oxygen, nitrate, and sulfate). These compounds at concentrations commonly found in groundwater were continuously administered for 4 years to a biofilm column reactor that resembled polluted groundwater environments. Acetate was the primary substrate to support microbial growth. Sequential biofilm zones or aerobic respiration, denitrification, and sulfate reduction developed within the column. Transformation of the halogenated aliphatic compounds coincided with the onset of sulfate in the column feed decreased the steady-state removals for several of the halogenated aliphatic compounds. These results suggest that sulfate was an important primary electron acceptor. Aerobic transformations of the chlorinated benzenes were incomplete due to the rapid depletion of oxygen and limited aerobic zone at the column inlet.

Influence of the choice of the boundary conditions on the results of the dynamic chromatography model

An investigation of the influence of the choice of the boundary conditions on the shape of the band profile obtained by simulation of the elution process using the classical model of semi-ideal chromatography is presented. As the boundary condition represents the perturbation created at the column inlet, it influences the response of the column. It is shown that the peak area is conservative only if certain conditions are satisfied. Among other approximations, the Houghton equation does not fulfil these requirements. Contour plots are used to illustrate the band migration process and the properties of these bands in non-linear chromatography.

The optimum taper angle for ethanol fermentation in a packed‐bed column reactor

AbstractIn ethanol fermentation, tapered columns facilitate the liberation of CO2 and, since the bed expands through a larger cross‐sectional area, smaller pressure drops occur. In this work, 0°, 2°, and 4° tapered columns, containing Saccharomyces cerevisiae entrapped in beads of K‐carrageenan, were operated for continuous production of ethanol from glucose. The column inlet diameters and the bead volume were maintained constant for the three columns. With decreasing taper angle, increasing feed glucose concentration, increasing feed flow rate and increasing bead volume in the reactor, the pressure drop across the bed increased. There was no significant difference between the ethanol productivities obtained in the 0°, 2°, and 4° tapered columns when a packed volume of 52% of the total volume was examined. Increasing the packed volume to 84% of the total caused the cylindrical column to become inoperable due to pressure buildup and bead compression. When the columns were packed to 84% capacity, the productivity and pressure drop values obtained on the 2° and 4° tapered columns did not significantly differ. For a feed concentration of 150 g glucose dm−3 and a residence time range of 5.4–15.94 h, the pressure drop varied between 4.5 × 103 and 1.28 × 104 Pa in the 2° and between 4 × 103 and 7.98 × 103 Pa in the 4° tapered column. Conversion in the 2° tapered column varied from 94% to 78.8% and in the 4° tapered column from 92.6% to 78.8%. Defining optimum taper angle as the smallest angle which allows for stable operation without any pressure buildup, the taper angle of 2° was selected as nearest to the optimum value.

Analytical Expression for Soil Water Diffusivity Derived from Horizontal Infiltration Experiments

AbstractA technique is developed that utilizes a rational function θ = (A1 + A3λ)/(1 + A2λ) to fit water content (or other liquid) profiles resulting from horizontal infiltration as used in the Bruce‐Klute method for determining soil water diffusivity. In the above function, θ is water content (L3 L−3), λ is the Boltzmann variable, and A1, A2, and A3 are constants. The Boltzmann variable, λ, is equal to xt‐0.5, where x is the distance from the inlet of a horizontal soil column and t is time from the commencement of liquid imbibition. The function is easily fit to experimental data by either linear or nonlinear regression techniques and leads to analytical expressions for sorptivity and soil water diffusivity without further numerical approximation or fitting. If boundary conditions are specified, only one of the three coefficients is left to be determined. The rational function provided excellent approximations to liquid distribution for water and alcohol horizontal infiltration experiments in this study and is adequate for representation of experimental data of several other researchers. An example is included to illustrate that the approach is also applicable to determination of diffusivity for the hot‐air method.

Effects of extracolumn convolution on preparative chromatographic peak shapes

The effect of extracolumn components on preparative (nonlinear) chromatographic peak shapes are investigated by convoluting column inlet and outlet profiles of chromatographic simulations with Gaussian and exponential spreading functions. Broadening of the inlet profile serves mainly to retard elution of the peaks. The chromatogram base line width is very sensitive to small amounts of broadening at the outlet (detector). While linear chromatography is modelled by simple shift-invariant convolution, nonlinear chromatography requires the more complex shift-invariant convolution model. This removes the property of variance additivity familiar in linear chromatography. The relative utilities of three measures of preparative chromatographic peak width are tested using the convoluted peak shapes obtained. 50 refs., 11 figs.

The role of retention gaps in routine whole oil biomarker analyses with cold on‐column injection

Utilization of whole oil biomarker analysis in oil prospecting through routine work with HRGC. Several measures, to prevent deposition of involatile material in the column inlet and to guarantee good resolution and sensitivity are proposed

The glass insert in stop-flow split injection

In stop-flow split injection the careful choice of the experimental conditions is of great importance for accurate quantitation, the size of the gaseous sample plug and its position with respect to the column inlet and to the top of the insert during the evaporation period are critical to prohibit sample vapour overflow and aerosol splitting. The proper insert design is established. A sample volume of 0.5 μl is recommended in the practical application of the stop-flow method.

Fast calculation of breakthrough curves in nonisothermal fixed‐bed adsorbers

Application of the fast Fourier transform, to the inversion of Laplace transforms is a recent development in the solution of equations describing chemical reactors. Hsu and Dranoff (1987) describe in detail how this method can be applied. Chen and Hsu (1987) use the fast Fourier transform for the prediction of breakthrough curves of an isothermal fixed-bed adsorber. The major strength of this approach is its speed of calculation. The purpose of the present work is to investigate the limits of the method and to show how this method can also be applied for nonisothermal adsorbers. Description of the Model A fixed-bed adsorption column, packed with porous spherical particles, is considered. At time zero, an adsorbable component is introduced in the column inlet flow. This introduces a step change in concentration and, possibly, in temperature. The transport phenomena in the adsorption column which are taken into account are axial dispersion, external film diffusion, pore diffusion, axial heat transfer in the solid and fluid phase, external film heat transfer, and heat transfer from fluid and solid phase to the wall. Radial gradients, the pressure drop across the bed, mass accumulation in the pores, and the heat capacity of the fluid in the pores, are neglected. Other assumptions are: concentration and temperature independence of heat capacities, densities and adsorption heat, and uniformity of the wall temperature. At the solid surface, the active component in the fluid phase is assumed to be in equilibrium with the adsorbed component in the solid phase; the involved heat effect is taken into account.

Sampling techniques for SFC using peak focusing by pressure and/or temperature programming

AbstractIn analogy to the focusing effective in capillary GC, performed with temperature programming but also with sectional cooling of the column inlet as in multidimensional capillary GC, peak focusing can easily be attained in SFC by adjustment of the mobile phase pressure as well as the column temperature. This may be of practical use in connection with sampling techniques giving poor, i.e. broad and unsymmetrical, peak shapes. Such disturbances may occur, for example, in time controlled valve sampling over longer switching times. Generally, all other negative influences on peak shape can be suppressed or compensated by trapping within the column inlet. Special trapping devices and “retention gaps” may also be coupled to the column inlet in order to create narrow starting plug widths. Positive pressure (density) and negative temperature programs give rise to peak compression besides the increase of peak capacity of the separation.

Models and experiments on adsorption columns with constant wall temperature—radially varying and radially lumped models

Theoretical studies were made on an adsorption column subjected to a step imposition of adsorbate at the column inlet, while the column wall was kept at constant temperature and the adsorption of a linear isotherm type took place. Two models were proposed for the prediction of concentration and thermal waves in the column: model I which considers the radial temperature profile in the column, and model II which assumes a uniform temperature over the column cross-section. Experiments were carried out for the adsorption of carbon dioxide on activated carbon in a column with constant wall temperature. The experiments showed that models I and II gave appreciably different heats of adsorption. A method was proposed for determining the intrinsic heat of adsorption based on model I from the overall heat of adsorption based on model II.

Practical aspects of the temperature dependence of the activity of uncoated and coated fused-silica columns in gas chromatography

Uncoated fused-silica capillary tubing has found widespread use in GC and GC/MS, e. g., in splitless and oncolumn injection, in the open-split interface used in GC/MS, and in hybrid fused-silica/glass capillary columns. As the uncoated capillary is usually more active than the coated one, it is very important to pay sufficient attention to the deactivation of the uncoated capillary. Otherwise the uncoated portion used as column inlet and/or outlet may become the main source of column activity and of analytical error. This case is especially serious under temperature-programmed runs. The effect of film thickness and temperature program on column activity is also discussed.

On the Fundamental Retention Equation in Gradient Elution Liquid Chromatography

Abstract Basic integral equations used to predict the solute retention times or volumes in gradient elution liquid chromatography are carefully examined. In order to simplify the integration procedure, one strongly suggests to select a convention independent of the solvent composition for defining the solute capacity factor. Most of these equations make use of the volume V′ of mobile phase which has passed through the peak center (or band maximum) as the integration variable. It is shown that, instead of V′, one can use the volume V flowing from the column in these equations as the integration variable in combination with retention conditions prevailing at the column inlet rather than actually within the column, provided that the gradient is displaced without modification through the column, i.e. without retention of the mobile phase components. The general retention equation is derived for a binary gradient where the strong component of the mobile phase is retained in such conditions that its distributio...

Continuous alpha-amylase production using Bacillus amyloliquefaciens adsorbed on an ion exchange resin

A method for the continuous production of extracellular alpha amylase by surface immobilized cells of Bacillus amyloliquefaciens NRC 2147 has been developed. A large-pore, macroreticular anionic exchange resin was capable of initially immobilizing an effective cell concentration of 17.5 g DW/1 (based on a total reactor volume of 160 ml). The reactor was operated continuously with a nutrient medium containing 15 g/l soluble starch, as well as yeast extract and salts. Aeration was achieved by sparging oxygen enriched air into the column inlet. Fermentor plugging by cells was avoided by periodically substituting the nutrient medium with medium lacking in both soluble starch and yeast extract. This fermentor was operated for over 200 h and obtained a steady state enzyme concentration of 18700 amylase activity units per litre (18.7 kU/l), and an enzyme volumetric productivity of 9700 amylase activity units per litre per hour (9.7 kU/l-h). Parallel fermentations were performed using a 2 l stirred vessel fermentor capable of operation in batch and continuous mode. All fermentation conditions employed were identical to those of the immobilized cell experiments in order to assess the performance of the immobilized cell reactor. Batch stirred tank operation yielded a maximum amylase activity of 150 kU/l and a volumetric productivity of 2.45 kU/l-h. The maximum cell concentration obtained was 5.85 g DW/l. Continuous stirred tank fermentation obtained a maximum effluent amylase activity of 6.9 kU/l and a maximum enzyme volumetric productivity of 2.73 kU/l-h. Both of these maximum values were observed at a dilution rate of 0.345 l/h. The immobilized cell reactor was observed to achieve larger volumetric productivities than either mode of stirred tank fermentation, but achieved an enzyme activity concentration lower than that of the batch stirred tank fermentor.

Application of the Convection‐Dispersion Model to Solute Transport in Finite Soil Columns

AbstractThe one‐dimensional convection‐dispersion model is investigated with respect to the proper boundary conditions to impose in applications to tracer movement in freely draining soil columns. It is shown that the model can be interpreted probabilistically and that this interpretation leads to physical restrictions on solute molecule transport through the inlet and exit boundaries of a soil column. These constraints, in turn, show that the correct exit boundary condition for a freely draining soil column is zero resident concentration or, equivalently, zero gradient in the flux concentration. This boundary constraint is combined with conditions appropriate to either an open or a closed inlet boundary to derive a variety of mass‐conserving solutions (some apparently new) to the convection‐dispersion model for both resident and flux concentrations. In particular, a new solution is presented for the resident concentration under a closed inlet boundary. The corresponding flux concentration solution for a constant solute flux at the inlet is shown to be the same as a solution first obtained by R.W. Cleary and D.D. Adrian (1973).