High efficiency packed column supercritical fluid chromatography of sulfonylurea herbicides and metabolites from large water samples

Summary Five sulfonylurea herbicides were separated by SFC on both a 25 cm and a 1.6 meter packed column. The former produced rapid analysis, the latter allowed high resolution of a complex mixture containing the solutes of interest. The solutes were simultaneously detected with UV, nitrogen-phosphorus (NPD), and electron capture (ECD) detectors. Peaks of breakdown products of sulfonylureas were characterized by their UV spectra and the presence or absence of nitrogen and chlorine from their NPD and ECD response. Both parent and breakdown products of sulfonylureas were on-line extracted from large water samples with detection limits as low as 50 parts per trillion.     

Capillary electrochromatography (CEC) in columns with different inner diameters

Summary Capillaries with different inner diameters (50–250 μm) were packed with the same stationary phase and their electrochromatographic performance was studied. Special focus was put on the currents measured in these capillaries and the necessity of controlling temperature, especially in capillaries of larger inner diameter. With a commercial instrument no loss in plate numbers was observed for a capillary with an I.D. of 180 μm and the corresponding Ohm plot was linear. A test mixture consisting of polar (weakly basic and acidic) and non-polar compounds was separated on packed capillaries with a range of inner diameters. No mass overloading could be observed if sample concentrations up to 5000 ppm were injected. On the other hand, when the injected sample volume exceeds 1% of the packed bed volume a decrease of the separation efficiency occurred. When the capillary I.D. was changed from 50 μm to 180 μm, peak heights and peak areas increased 5 to 6-fold. As a consequence the detection limits of the 180 μm I.D. capillary were 5.6–7.5 times lower than those obtained in a 50 μm I.D. capillary. Dedicated to Professor Dr. Heinz Engelhardt on the occasion of his 65^th birthday.     

A correlation for yield stress fluid flow through packed beds

Relatively few correlations are available for non-Newtonian fluid flows through packed beds, even though such fluids are frequently used in industry. In this paper, a correlation is presented for yield stress fluid flow through packed beds. The correlation is developed by introducing the yield stress model in place of the Newtonian model used in deriving Erguns equation. The resulting model has three parameters that are functions of the geometry and roughness of the particle surfaces. Two of the parameters can be deduced in the limit as the yield stress becomes negligible and the model reduces to Erguns equation for Newtonian fluids. The third model parameter is determined from experimental data. The correlation relates a defined friction factor to the dimensionless Reynolds and Hedstrom numbers and can be used to predict pressure drop for flow of a yield stress fluid through a packed bed of spherical particles. Conditions for flow or no-flow are also determined in the correlation. Comparison of model calculations, between a Newtonian and a yield stress fluid for flow penetration into a packed bed of spheres, shows the yield stress fluid initially performs similar to the Newtonian fluid, at large Reynolds numbers. At lower Reynolds numbers the yield stress effect becomes important and the flow rate significantly decreases when compared to the Newtonian fluid.     

Are axial and radial flow chromatography different?

Radial flow chromatography can be a solution for scaling up a packed bed chromatographic process to larger processing volumes. In this study we compared axial and radial flow affinity chromatography both experimentally and theoretically. We used an axial flow column and a miniaturized radial flow column with a ratio of 1.8 between outer and inner surface area, both with a bed height of 5 cm. The columns were packed with affinity resin to adsorb BSA. The average velocity in the columns was set equal. No difference in performance between the two columns could be observed. To gain more insight into the design of a radial flow column, the velocity profile and resin distribution in the radial flow column were calculated. Using mathematical models we found that the breakthrough performance of radial flow chromatography is very similar to axial flow when the ratio between outer and inner radius of the radial flow column is around 2. When this ratio is increased, differences become more apparent, but remain small. However, the ratio does have a significant influence on the velocity profile inside the resin bed, which directly influences the pressure drop and potentially resin compression, especially at higher values for this ratio. The choice between axial and radial flow will be based on cost price, footprint and packing characteristics. For small-scale processes, axial flow chromatography is probably the best choice, for resin volumes of at least several tens of litres, radial flow chromatography may be preferable.     

High efficiency HPLC with long packed columns

Coupling several 25 cm × 2 mm ID analytical columns together is a simple and easy way to achieve high resolution HPLC (20,000–50,000 plates). How to do this with commercially available instruments, injectors and detectors is described in the paper. An attractive feature of the long narrow column approach is that the same HPLC set-up can be used for both fast-low and slow-high efficiency separations. High efficiency is essential for really complex natural mixtures, e.g. the hop and beer bitter acids. Some examples are shown.     

Determination of alcohols in gasoline blends using a multi-dimensional switching system

Methanol, 2-Me-propanol-2, propanol-2, benzene, toluene and xylenes in gasoline blends were determined using a valveless multi-dimensional switching system (MDSS) with two packed columns and temperature programming. Compounds of interest, interfering with paraffins and naphthenes, were in a sequence of four heart cuts transferred onto the second column. The resulting baseline separation enabled precise quantitative measurement within a short analysis time. Instrument settings, times of switching and integration parameters were stored in an instrument memory file (user table) and thus high precision in the measurements was achieved.     

High performance liquid chromatography of terpenoids

HPLC-separation using a reversed-phase system is described for phytosterols, pentacyclic triterpenoid acids, -diols and –ketones.     

Mathematical simulation of radial heat transfer in packed beds by pseudohomogeneous modeling

Uniform flow regime and constant effective thermal conductivity inside packed beds are commonly accepted in the evaluation of the fluid dynamics and heat transfer in such systems.However,several authors have confirmed the presence of an oscillatory velocity profile caused by the effective contribution of porosity profile in the fluid dynamic behavior of packed beds,which directly influences the heat transfer inside the beds.This paper describes the application of a pseudo-homogeneous mathematical ...