Separator column length

The column length and inner diameter are the two most important features required in column generation on microchips. The column separation capacity is measured in terms of number of plates, which is proportional to column length. But back pressure and analysis time are raised proportionally as column length increases. For gradient separations, column length is less a factor for resolution as separation is controlled by gradient rather than... 

The number of theoretical plates and, thus, the separation efficiency, is determined by the length of the separator column. If two separator columns are used in series, the resulting enhancement of separation efficiency leads to a better resolution between ions with similar retention characteristics, with a corresponding increase in retention times. The separator column length also determines the exchange capacity. An increase of the exchange capacity via elongation of the separator column is recommended in all cases where the ion to be analyzed is present in an excess of another component. 

Figure 16.10 Calculated zone profiles in displacement chromatography, fcy j = fc/,2 = fc/,d = 50 s. Solid gray line first component thin solid black line second component fat solid black line displacer. Characteristic of the separation Column length 25 cm. Phase ratio 0.25. Flow velocity 0.05 cm/s. Competitive Langmuir isotherm with coefficients = 18.75 fl2 = 22.5 = 27 bi = 12.5 i>2 = 15 bj = 18 2,1 = 1.20. Loading factors Ly =...

The reaction coil is 20 cm of coiled stainless steel capillary tubing. The guard column (1.5 cm length, inside diameter) which protects the more expensive Cjg reversed-phase separating column (length = 30 cm, inside diameter = 3.9 mm) is packed with silica-based Cig material. Typical electrochemical detector cells which can be used are (i) Model TL-5 thin layer detector cell obtained from Bioanalytical Systems, (ii) Model EA 1096 wall jet detector cell obtained from Metrohm. 

Recovery factor Reduced column length Reduced plate height Reduced velocity Relative retention ratio Retardation factor d Retention time Retention volume Selectivity coefficient Separation factor... 

Now, the column length (L) can be defined as the product of the minimum plate height and the number of theoretical plates required to complete the separation as specified by the Purnell equation. 

Figure 5. Graph of Log of Column Length against Separation Ratio of the Critical Pair...

The column length will actually increase as (l/(a-l)3). This means that the column length is extremely sensitive to the separation ratio of the critical pair and explains... 

The minimum column length was calculated for a series of separation ratios using equation (19) and the results obtained are shown in Figure 14. 

Generally, optimizing the selectivity by choosing a gel medium of suitable pore size and pore size distribution is the single most important parameter. Examples of the effect of pore size on the separation of a protein mixture are given in Fig. 2.15. The gain in selectivity may then be traded for speed and/ or sample load. However, if the selectivity is limited, other parameters such as eluent velocity, column length, and sample load need to be optimized to yield the separation required. 

Many operating variables, such as sample volume, flow rate, column length, and temperature, must be considered when performing any separation. The relative importance of these variables for Toyopearl HW-55F resin columns has been specifically evaluated. For example. Fig. 4.47 shows the relationship between column efficiency, or height equivalent of a theoretical plate (HETP),... 

For production-scale separations, column diameters up to 30 cm are recommended. Usually the length of the column is in the range of 600-1200 mm for smaller column diameters (less than 50 mm). Columns with larger diameters can be packed up to 900 mm. 

FIGURE 7.6 Effect of column length on the separation efficiency. Two different Fractogel EMD BioSEC columns (A 600 X 16 mm, B 1000 X 16 mm) were tested using BSA, ovalbumin, and cytochrome c (S/S/3 mg/ml) as sample (20 m/VI sodium dihydrogen phosphate, 300 m/VI NaCI, pH 7.2 0.5 ml/min). Better resolution can be achieved using longer columns. 

The C8 (octyl reverse phase) is the general "work horse" of reverse phases and is recommended as the first to be tried when attempting to exploit dispersive interaction to achieve a separation. Columns packed with C8 material are available in range of lengths from 3 to 50 cm long and can be packed with particles 3, 5, 10 and 18 m in diameter. Consequently, a wide range of column efficiencies is available to the analyst, which, in the methods development laboratory, should always be readily accessible. 

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