Columns smaller-particle

Particle size affects the pressure drop through the column. Smaller particle size leads to higher pressure drops for a given flowrate. Often, hydraulic limitations are the most important consideration in design. Particle size also affects the relative magnitude of transport Steps 2 and 3 listed above. This is analogous to the discussion on this point in Chapter 7 Adsorption. 

The majority of carotenoid separation has been carried out with 5 pm Cl 8 spherical particles packed in a 250 x 4.6-mm column. However, shorter and narrower (narrow bore) columns, smaller particles, and C30 stationary phases are increasingly used. 

Higher resolution can be obtained by longer/coupled columns. Smaller particles have limited effect on the resolution. 

Based on the requirements of the separation, media of suitable pore size, particle size, and surface properties are selected as well as column dimensions and column material. In some cases a suitable combination of media type and column dimensions may be available as a prepacked column. In most cases, this is a more expensive alternative to preparing the column yourself but will provide a consistent quality as assured by the manufacturing and testing procedures of the vendor. The consistent quality may be critical in obtaining reproducible results and may thus be a cost-effective solution. Also, the fact that smaller particle-sized media are more difficult to pack and require special, and expensive, equipment has resulted in that gel filtration media of small particle size, e.g. smaller than 15 /zm, are predominantly supplied as prepacked columns. 

TSK-GEL PW and TSK-GEL PWxl columns are shown in Pig. 4.11. Although many methods for polymer analysis have been developed satisfactorily on TSK-GEL PW columns, higher resolution can often be achieved with a TSK-GEL PWxL column. The smaller particle sizes of the resins packed in TSK-GEL PWxL columns provide almost 2.5 times the resolution of their TSK-GEL PW counterparts. In addition, with shorter TSK-GEL PWxl columns, higher resolution separations are possible in less than half the time, as shown in Pig. 4.12. 

Small particle size resins provide higher resolution, as demonstrated in Fig. 4.41. Low molecular weight polystyrene standards are better separated on a GIOOOHxl column packed with 5 /u,m resin than a GlOOOHg column packed with 10 /Ltm resin when compared in the same analysis time. Therefore, smaller particle size resins generally attain a better required resolution in a shorter time. In this context, SuperH columns are best, and Hhr and Hxl columns are second best. Most analyses have been carried out on these three series of H type columns. However, the performance of columns packed with smaller particle size resins is susceptible to some experimental conditions such as the sample concentration of solution, injection volume, and detector cell volume. They must be kept as low as possible to obtain the maximum resolution. Chain scissions of polymer molecules are also easier to occur in columns packed with smaller particle size resins. The flow rate should be kept low in order to prevent this problem, particularly in the analyses of high molecular weight polymers. 

SEC columns have become much more efficient since they were introduced in the late 1950s. The major factor for this has been the ability of synthetic polymer chemists to produce smaller particle sizes of column packing materials. The first sorbents were several 100 /mm wide in diameter (20), whereas modem columns are filled with particles in the range between 3 and 20 /mm, which caused an immense improvement in separation power. The major drawback... 

For organic SEC separations the use of polystyrene/divinylbenzene (PS/ DVB) particles is almost universal throughout the industry. Polymer Laboratories PS/DVB material, PLgel, which is produced in a series of individual pore sizes, formed the basis for the original product line of SEC columns. Developments in the refinement of particle sizing introduced the benefits of smaller particle size and more efficient columns, which significantly reduced SEC analysis time through a reduction in the number of columns required for... 

Tables 21.3 and 21.4 show the results of our evaluation on a column set that we felt performed very well. These tables address criteria 1 through 5 described previously. We judged the values listed to be very acceptable for high temperature GPC applications. For room temperature applications, where a smaller particle size column could be used, better values would be expected.

As particle size decreases, hydrogen leakage decreases and hot spot temperature in the bed is higher. Thus the smaller particle size has greater activity (see Table VI). A kinetic system which defines the reaction in terms of CO and C02 methanation and CO shift conversion was used to determine the activity (see last column of Table VI). 

We first note the very large differences in column performance for the two methods. Effective plates per second represents the speed characteristics of a column (e.g., the number of plates that can be generated in a given time interval) (13). As can be seen, HPLC is 100 to 1000 times faster than classTcal LC. (We shall discuss the differences between PLB and PB in the next section.) This improved performance arises mainly from the use of significantly smaller particle sizes in HPLC. Moreover, in classical LC, the mobile phase is delivered to the column by gravity feed, hence, the very low mobile phase velocities. In HPLC, it is desireable to improve performance... 

Below the dotted line in Table I we list less fundamental differences between the two methods. Column lengths tend to be somewhat shorter in HPLC using small particle PB as a consequence of the high efficiencies that can be generated with the smaller particle sizes. For analytical scale HPLC, tube diameters of 3-4 mm are selected however, for preparative scale, tube diameters of 1 cm or above are not uncommon. 

Figure 30 shows the results of an experiment in which a solution of Q-CdS was fractionated by exclusion chromatography in a column of sephacryl-gel This column material has holes which the smaller particles penetrate and reside in for some time. The first fraction therefore contains the larger particles. The upper part of the figure shows the absorption spectrum of the starting material, and the lower part the spectra of six fractions. The first fraction has an unstructured spectrum beginning at... 

Stationary phase. Supelcosil Cig ABZ (Supelco Scientific, Bellefonte, PA, USA) was the most often employed support and gave the best correlations. This stationary phase should be selected in a first instance with a geometry adapted to the application for conventional gradient experiments, supports of 150X4.6 mm, 5 pm represent a good choice while a shorter column (i.e. 50 mm or lower) with smaller particle size (i.e. 3-3.5 pm) must be preferentially selected for fast gradient analysis. 

Flow rate. Its value must be selected according to the column geometry and back-pressure Umitations of the system. For 4.6 mm internal diameter columns (5 pm), 1 mLmin is adapted for a conventional length, while for short columns packed with smaller particles the flow rate can be increased. 

The peak volume is directly proportional to the square of the column diameter and the column length and decreases with Increasing column efficiency (decreases for smaller particle packings). The concentration at the peak maximum, C—, is given by... 

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