Efficiency of column

Figure 1 highlights the separation of a mixture of different polarity GC standards known as the "Grob mix" commonly used to test the efficiency of columns. Figure 2 shows the linear representation highlighting the closeness of elution time if only a single column had been employed. The identity of the mix chemicals and their retention times are given in Table 3. 

Because of the problems encountered with the water system, the use of aliphatic alcohols, ie.g., methanol, ethanol, and isopropanol, as modifiers of the adsorption strength has been recommended (44. 45. 50. 51). Usually, between 0.01 and 0.5% (v/v) alcohol is added to the eluent. As an example, the k values for the benzyl alcohols on a silica column are in the same range when eluted with dichloromethane containing either 0.1% water (50% water-saturated) or 0.15% methanol or 0.3% isopropanol (45). The preparation and preservation of these alcohol-eluent mixtures is accompanied by problems similar to those discussed with water-modified eluents. Also, column equilibration is slow (44). The efficiency of columns operated with alcohol-modified eluents is generally lower than that of water-modulated eluent system. At some alcohol concentrations, distorted peaks with tailing or frontal asymmetry have been observed 44), but olhei workers using another silica could not verify this observa tion (61). 

The efficiency of column (n) in number of theoretical nlates has bn shown to be given by the following equation,... 

Efficiency of column. Usually measured by column theoretical plate number. Relates to peak sharpness or column performance. 

Hengstebeck, R., Contacting Efficiencies of Column Internals, Distillation Principles and Design Procedures, Robert E. Krieger, 1976, Chap. 10. 

Gritti F, Cavazzini A, Marchetti N, Guiochon G (2007) Comparison between the efficiencies of columns packed with fully and partially porous C18-bonded silica materials. J Chromatogr A 1157(l-2) 289-303. doi S0021-9673(07)00878-3 [pii] 10.1016/j.chroma.2007.05.030... 

On the other hand, the lack of internal pore structure with micropellicular sorbents is of distinct advantage in the analytical HPLC of biological macromolecules because undesirable steric effects can significantly reduce the efficiency of columns packed with porous sorbents and also result in poor recovery. Furthermore, the micropellicular stationary phases which have a solid, fluid-impervious core, are generally more stable at elevated temperature than conventional porous supports. At elevated column temperature the viscosity of the mobile phase decreases with concomitant increase in solute diffusivity and improvement of sorption kinetics. From these considerations, it follows that columns packed with micropellicular stationary phases offer the possibility of significant improvements in the speed and column efficiency in the analysis of proteins, peptides and other biopolymers over those obtained with conventional porous stationary phases. In this paper, we describe selected examples for the use of micropellicular reversed phase... 

Using the efficiency of the column to your advantage Calculation of efficiency Proper choice of flow rate Comparison of efficiencies of columns Recycle chromatography Analytical recycle Preparative recycle... 

The total exergy losses consist of configuration limitations due to the design of the column and transportation limitations due to the states of streams. For Exsv > o, the exergy efficiency of column i becomes... 

Table 4.17 shows that column 2 operates with efficiency as low as 4.1%, while the efficiency of column 1 is 50.6%. The exergy values for the whole separation system of two columns are also low and need to be improved. The individual values of PI show that it is possible to reduce by 13.1% the total loss of 0.834 MW in column 1 and by 19.1% the total loss of 27.813 MW in column 2. Despite the heat integration, the separation section of the methanol plant performs poorly in utilizing the exergy in the distillation columns. 

Kennedy and Knox [274] compared the performances of Porasil, Corasil, Corning Porous Glass and Zipax for retained and unretained organic solutes. The performance of Zipax and the efficiency of columns of different particle size have been studied [275]. The performance of Permaphase ETH and Permaphase ODS, pellicular materials consisting of silicones bonded to silica, has also been investigated [276]. 

Obviously, H is the measure of the column efficiency that is independent of the total column length. The HETP is usually expressed in the unit of length such as millimetre. The smaller HETP means higher efficiency of column. 

A thallium nitrate column is stable for several weeks at 100°C and can be used for 180h at 130°C without selectivity loss. A silver nitrate colunm can be used for 180h only at 60°C. Unfortunately, the efficiency of columns containing thallium salts is lower than that of silver salts. 

N calculated this way using is a measure of the efficiency of the whole system that includes the dead volume. In order to calculate and compare efficiencies of columns alone, it is necessary to use (adjusted retention time) in place of tR in the above expression, to obtain the effective plate number. 

Table I. Denitrification capacity and efficiency of column reactors using immobilized P. aeruginosa...

Liquid maldistribution affects mass transfer efficiency of columns. However, in tray columns maldistribution is restricted to a single tray since the hquid is well mixed in the subsequent downcomer and evenly redistributed to the next tray. In this respect, tray columns are better suited for large diameter columns than packed... 

Figure 6-48 gives a brief summary of the separation efficiency of columns, with in-... 

Diffusion and dissolution of substances chromatographed on stationary phases are determined by the mass transfer resistance, which affects the efficiencies of chromatographic columns. Efficiencies of columns with LCSPs are generally lower than those of columns with conventional stationary phases. Therefore, mixtures of LCSPs with conventional stationary phases can be advantageous. The mixture of a liquid crystal with a conventional stationary phase increases the efficiency of a column by improving the homogeneity of the stationary phase film on the wall of a capillary column. The mixture of two hquid crystals can also prove advantageous. The properties of combined stationary phases are described elsewhere. ... 

The use of the concept of the reduced plate height, h, which is the quantity H divided by dp and the reduced velocity, V, given by V = udp/Dm is of practical advantage in the comparison of the efficiency of columns packed with particles of different diameters and in theoretical treatments. However, the discussion of the reduced plate height is out of the scope of this book and one who is interested in this problem should consult other related books [e.g., ref. 9]. 

Reduced plate height allows us to compare the efficiency of columns with different particle sizes or different internal diameters (in open capillary columns). 

The Efficiency of Columns Packed with Shell Particles 147... 

THE EFFICIENCY OF COLUMNS PACKED WITH SHELL PARTICLES... 

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