Large-diameter Column Research Articles

Effect of radial gradient of temperature on the performance of large-diameter high-performance liquid chromatography columns: I. Analytical conditions

The performance of a large-diameter chromatographic column can be drastically reduced when the solvent enters the column at a temperature different from that of the wall of the column. A radial temperature gradient inside the column will affect the physical properties of the solvent and the chromatographic behaviour of the solute resulting in a deformation of the band profile. A mathematical model is proposed to take into account the effect of a radial gradient of temperature in a large-diameter column on the chromatographic peak shape under linear conditions. The model is then compared with experimental results in preparative columns of different sizes. A good agreement between experiment and theory has been found showing a serious effect of thermal conditions on separation quality, depending on the column size. It is also demonstrated that a small difference of temperature can be helpful to compensate practical effect of frits and distribution of the sample at the extremities of the packed bed. Finally, it demonstrates the necessity to perform efficiency measurement under different thermal conditions to have a good comparison between columns.

Temperature gradients in preparative high-performance liquid chromatography columns

One rarely investigated but important factor in the performance of HPLC columns is temperature. It influences the thermodynamic and hydrodynamic properties of the column. The subject of this work is the distribution of temperature within the column bed. Analytical columns operated at high flow-rates, and large diameter columns packed with small particles are subject to viscous heat dissipation which can seriously affect the quality of the separation. Since the thermal conductivity in a packed column is rather weak, axial and radial temperature profiles will appear in the chromatographic bed. The present paper reports temperature profiles measured in a preparative LC column of 60 mm diameter as a function of the packing material, the eluent flow-rate and the eluent composition. Van Deemter plots show the influence of temperature on the separation process. The influence of the operating parameters on the performance of the column is discussed.

Interaction of steep waves with offshore structures

Offshore structures having large diameter columns at the waterline cause a significant disturbance to the ambient wave field, and large run–up around the columns. The paper discusses prediction of this effect in regular sinusoidal waves and in focused wave groups characteristic of extreme storm waves. Results are obtained from linear and second–order nonlinear analytical solutions for vertical circular cylinders. For very large waves, however, a fully nonlinear analysis is needed, which must be based on numerical discretization in both temporal and spatial dimensions. A finite–element procedure for predicting the interaction of steep waves with offshore structures is briefly introduced.

Heat Conduction of Fixator Pins with Polymethylmethacrylate External Fixation

SummaryThe purpose of this study was to determine the degree of thermal conduction along the fixation pins associated with acrylic external fixators and to develop a means of minimizing the potential for thermal injury. The data suggest that the degree of temperature conducted with 1.9 cm diameter acrylic external fixators was of minimal clinical significance if maintained a distance of one centimeter from the patient’s tissues. Larger diameter columns increase the potential for injury, however, this can be minimized with the use of a constant saline drip at the pin-acrylic interface to facilitate heat loss.This article describes the evaluation of thermal properties of polymethylmethacrylate external skeletal fixators. The data demonstrate heat conduction along the fixation pins. Thermal injury is theoretically minimized if columns are maintained a distance of at least one centimeter from the patient’s tissue.Research supported in part by and presented for the University of Missouri Pi Chapter of the Honor Society of Phi Zeta in coordination with SmithKline Beecham Animal Health, April 7, 1994

Temperature of the eluent: a neglected tool in high-performance liquid chromatography?

The influence of eluent temperature on efficiency in high-performance liquid chromatography with special reference to the role of viscous heat dissipation is investigated for water-jacket and air-bath thermostatted columns. When separations are performed on well-thermostatted large-diameter columns packed with small particles or on analytical columns operated at high flow-rates, the additional thermostatting of the eluent to a specific temperature below the column temperature turns out to have some advantages. The precooled eluent causes the development of a temperature profile in a radial direction which is opposed to and compensates the radial temperature profile in the column caused by viscous heat dissipation. For columns that are thermostatted in an air bath, a similar effect is observed, but the strong dependence of the column temperature on the eluent temperature results in a poor reproducibility if the eluent is not thermostatted itself.

Application of γ-ray Attenuation for Measurement of Gas Holdups and Flow Regime Transitions in Bubble Columns

In this study a γ-ray densitometry was used to measure radial and axial volume fraction distributions in a 0.21 m diameter bubble column, and flow regime transitions in a 0.05 m and 0.21 m diameter bubble columns. Experiments were conducted with two- and three-phase systems (nitrogen−Fischer−Tropsch derived waxes−iron oxide or silica particles) in both batch and continuous modes of operation at 265 °C and ambient pressure. Average radial gas holdups in the large diameter column showed the existence of a maximum at the center of the column, in both two- and three-phase systems. The maximum was more pronounced at higher superficial gas velocities (churn-turbulent flow regime). The axial and average gas holdup measurements in two-phase systems were in good agreement with results obtained by a conventional method (pressure measurements along the column height). An independent treatment of all three phases did not yield satisfactory results, due to large impact of small experimental errors on calculated holdup...

Determination of the apparent transverse and axial dispersion coefficients in a chromatographic column by pulsed field gradient nuclear magnetic resonance

Pulsed field gradient nuclear magnetic resonance permits the direct determination of the coefficient of apparent dispersion of a solute in a chromatographic column. Axial and transverse dispersion coefficients can be measured independently as a function of the flow velocity of the mobile phase. Experiments have been carried out using water as the mobile phase, porous C18 silica as the stationary phase, and water as the probe (self-dispersion). The results are reported and compared to similar ones obtained previously by various authors, using conventional chromatographic techniques. The NMR method shows potential for the investigation of the structure and homogeneity of the packing of large diameter columns for preparative chromatography. It permits direct access to local values of these coefficients instead of measuring averages as classical methods do.

Gas distribution in large-diameter packed columns

Abstract The aim of the present work was to determine the extent of gas maldistribution in large-diameter columns containing corrugated-sheet structured packings. A large-diameter column simulator has been designed for this purpose (cross section, 3 m × 0.5 m; packed bed height, 4.4 m) with 15 independent inlets for gas, allowing the introduction of diverse initial distribution profiles. The gas velocity profiles leaving the top of the packed bed are discussed in terms of lateral spreading and observed effects of gas load, liquid load and the height of the packed bed.

SANDWICH LOAD CELLS

The photograph shows one of a batch of 'sandwich' load cells made up to answer a common problem; a relatively large diameter column passes through a fixed structure with a remote control tool at the end of the column. It was required to measure and control the load exerted between the column and the surrounding fixed structure.

Behavior of 78 Pesticides and Pesticide Metabolites on Four Different Ultra-Bond Gas Chromatographic Columns

The gas chromatographic (GC) elution order and relative retention time data (compared to aldrin) are presented for 78 pesticides and pesticide metabolites on 4 different types of commercially available 2 mm id Ultra-Bond columns including Ultra-Bond 20M (20M), Ultra-Bond 20SE (20SE), Ultra-Bond 20M coated with 1% OV-210 (OV-210), and Ultra-Bond 20M coated with 0.5% OV-210 + 0.65% OV-17 (mixed phase). Relative retention time data (compared to parathion) are also represented for 19 organophosphorus insecticides on the 4 Ultra-Bond columns evaluated. Corresponding 4 mm id Ultra-Bond columns were evaluated at the same time as the 2 mm id columns, and results and comparisons for these larger-diameter columns are discussed. These data indicate that, with aldrin as a reference peak, a complement of the mixed-phase column and either the 20M, the 20SE, or the OV-210 column represents a useful chromatographic tool for dual-column analysis of pesticide residues. The 2 mm id columns were more useful in chromatographing later-eluting pesticides whereas the corresponding 4 mm id columns were more useful in chromatographing earlier-eluting pesticides.

Preparative Liquid Chromatography and theH/uCurve

Abstract H/u curves for columns of increasing internal diameter are shown to be useful for evaluating their LC performance. In particular, the H/u curve reveals whether the packing technique or the packing material is defective. H/u curves for very large internal diameter columns show deviations which result from friction heat and thermal expansion of the column tubing, creating a void at the column wall.

Hydraulic, mass transfer and heat transfer performance comparison between ordered bed packing and sieve trays

AbstractThe Girdler–Sulfide (GS) heavy water production process has traditionally used tray columns because of their large size. In recent years, the chemical industry has extended the use of packing to larger columns because of economic and performance advantages. A pilot scale study was thus initiated to compare the hydraulic, mass transfer and heat transfer performance of an ordered bed packing (Mellapak) with sieve trays operating under GS process conditions. Mellapak offered lower pressure drops, higher throughputs and improved heat transfer over sieve trays. However, benefits to deuterium mass transfer were only marginal in large diameter columns.

Rapid method for determining desmosine, isodesmosine, 5-hydroxylysine, tryptophan, lysinoalanine and the amino sugars in proteins and tissues

A rapid and sensitive chromatographic method is described for determining desmosine, isodesmosine, 5-hydroxylysine, tryptophan, lysinoalanine, glucosamine and galactosamine at picomole levels in protein and tissue hydrolysates. This method uses either an automated amino acid analyser with a 17.5 x 0.28 cm microcolumn packed with 6.0 ± 0.5 μm spherical resin, thermostated at 52°C, one buffer system (0.21 M sodium citrate, pH 5.125) and 3-nitrotyrosine as the internal standard, or conventional instruments using the same system but with larger diameter columns and resins (11.0 ± 1.0 μm). This method should be especially valuable for determining collagen and elastin in tissue hydrolysates from the amounts of 5-hydroxylysine, and desmosine or isodesmosine present, respectively, and for studying protein hydroxylation, glycosylation, cross-linking formation, and the turnover rates of collagen and elastin in normal and diseased tissues.

Firestorms

Quantitative criteria are sought for onset of firestorms, severe stationary (non-propagating) holocausts arising via merger of fires from multiple simultaneous ignitions in a heavily fuel-laden urban environment. Within an hour, surface-level radial inflow from all directions sustains a large-diameter convective column that eventually reaches altitude of about 10 km (e.g., Hamburg, Dresden, Hiroshima). As the firestorm achieves peak intensity (a couple of hours after the ignitions), inflow speeds are inferred to attain 25–50 m/s; typically 12 km2 are reduced to ashes, before winds relax to ambient levels in six-to-nine hours. Here the firestorm is interpreted to be a mesocyclone (rotating severe local storm). Even with exceedingly large heat release sustained over a concentrated area, in the presence of a very nearly autoconvectively unstable atmospheric stratification, onset of vigorous swirling on the scale of 2 hrs requires more than concentration of circulation associated with the rotation of the earth; rather, a preexisting, if weak, circulation appears necessary for firestorm cyclogenesis.

Large-diameter plasma columns produced by surface waves at radio and microwave frequencies

Up to now, the production of plasma columns through the propagation of electromagnetic surface waves had been reported essentially in the microwave range (200 MHz–10 GHz), with tube diameters that extend from 0.5 to 40 mm. Such plasmas can be obtained at much lower frequencies, at least down to 27 MHz. We also present larger plasma column diameters, up to 124 mm, as well as column lengths up to 6 m. The surface wave dispersion and the axial electron density distribution observed under these new conditions are well described by the cold plasma model.

Influence of thermal conditions on the efficiency of high-performance liquid chromatographic columns

The effect of thermal conditions on efficiency in high-performance liquid chromatography is investigated with special reference to the role of the viscous heat dissipation. In systems thermostatted by a water-bath or jacket it turns out to be advantageous to pre-cool the mobile phase when high flow-rates and small particle sizes are used. This is explained by a compensation of band broadening in the first and second part of the column. The wall region of the band moves faster in the first part, but it moves slower in the second part and it is eluted together with the solute from the core region. Our results indicate that a similar compensation effect occurs when the column is operated in still air. This is due to back-flow of heat through the stainless-steel column wall. For large diameter columns (larger than 3 mm), packed with small particles, a linear temperature profile imposed on the column wall may diminish the detrimental effects of viscous heat dissipation. Results obtained with such a system are promising.

Application of capillary gas chromatography to automated on‐line quantitative analysis of solvent vapors

AbstractSolvent vapors in air may be measured with capillary gas chromatographic columns. By using large diameter columns and sample loops of approximately the same internal diameter, the column may be connected directly to the gas sampling valve. This approach eliminates the use of a splitter or cryogenic trapping and allows low levels to be measured. By operating the column at high velocity, column efficiency is sacrificed for increase in speed.

Modeling the Fischer-Tropsch synthesis in the slurry phase

A model of the FT synthesis in the slurry phase is being developed. It is based on first-order rate expression for hydrogen consumption but considers all relevant hydrodynamic phenomena. The parameters involved in the model equations were estimated from literature correlations and recent experimental results. The basic set of operational conditions was that applied in the Rheinpreussen-Koppers demonstration plant. The computations show that liquid solid mass transfer resistances and catalyst settling can be neglected in larger diameter columns. Gas-liquid mass transfer limitations are also small as long as conventional catalysts and favorable gas velocities are applied. The simulated results are in general agreement with practical experience. 52 refs.

The Influence of Voltage Grading and Insulation Length on Contamination Performance

The results of experiments made to determine the effect of voltage distributions on the ac contamination performance of insulators are described. By using both internal and external capacitive grading, the voltage distributions on long insulator strings were varied from highly uniform to highly nonuniform. Results of contamination tests made on these insulators with clean fog are presented, and the impact for insulation design is discussed. Additional contamination test data on long post-type insulators are given. An analysis of these results shows that a potentially severe design problem exists for such insulators if large diameter columns are used for supports or on apparatus in substations located in contaminated areas.

Preparative counter-current chromatography with a slowly rotating glass coil

An attempt to scale-up the preparative capacity of counter-current chromatography was successfully made by the use of a large-bore glass coiled column slowly rotating in the gravitational field. The capability of the present scheme was demonstrated in separations of dinitrophenyl amino acids on a two-phase solvent system composed of chloroform-acetic acid-0.1 N hydrochloric acid (2:2:1). The methods enables efficient separations of 600-mg samples in 10 h with a good recovery. The present scheme is amenable to be further scaled-up by the use of longer and/or larger-diameter columns.