Flow rate and column length

Effect of Flow Rate and Column Length on Breakdown Time and kco/3.3 Initial concentration, 1.0%... 

Effect of Initial Concentration, Flow Rate, and Column Length on k... 

Since the optimization is performed simultaneously on three parameters, i.e. the amount loaded, flow rate and column length, it is necessary to relate the flow rate to the plate count. This is done in dimensionless units. The flow rate is written as the reduced velocity (Eq. (7.50)). 

Figure 6 Effect of flow rate and column length on separation in gradient elution, with (fc /KnO) held constant. Cb column 8-40% acetonitrile-water gradient, (a) fo = 15 min, 8-cm column, 2mL/min, (b) 30 min, 8-cm, 1 mL/min. From Ref. 9.)...

As mentioned in Section 11.8.4, the parameters that are most important for a qualitative analysis using most GC detectors are retention time, tR adjusted retention time, t R and selectivity, a. Their definitions were graphically presented in Figures 11.16 and 11.17. Under a given set of conditions (the nature of the stationary phase, the column temperature, the carrier flow rate, the column length and diameter, and the instrument dead volume), the retention time is a particular value for each component. It changes... 

The other parameters of the separation, such as the mobile-phase composition, gradient range (A%B), and column temperature, should be kept the same. A difference in particle size between columns does not affect the geometric scahng relationships however, the location on the H versus u curve (i.e., column efficiency) and the column backpressure may change, which may require an increase or decrease in flow rate or column length. 

In a uniform colonm the isothermal retention volume V is related to eluent-gas flow rate F, column length L, and average band velocity (dzjdtXy, by the expression... 

The permeability of a device can be determined from flow rate, viscosity, column length and pressure as outlined in Section 2.2.5. Now we have accomplished what we have set out to do we have linked the performance parameter, the speed of analysis and the pressure to each other. All performance parameters can thus be determined from externally measurable observations without reference to the internal content of the chromatographic device ... 

During the last ten years, aqueous SEC has caught up with non-aqueous SEC with respect to speed and resolution, and is now a very powerful tool for characterizing or purifying water-soluble polymers. Rapid separations of various types of water-soluble polymers with high resolution and without sample-support matrix interaction are possible. However, the selection of suitable eluent is very important for obtaining satisfactory results. Appropriate selection of other conditions such as flow rate, temperature, column length, pore size of support, sample concentration and injection volume are also important. 

Conventionally, analytical SEC columns have been produced with an internal diameter of 7.5 mm and column lengths of 300 and 600 mm. In recent years environmental and safety issues have led to concerns over the reduction of organic solvent consumption, which has resulted in the development of columns for organic SEC that are more solvent efficient (13). By reducing the internal diameter of the column, the volumetric flow rate must be reduced in order to maintain the same linear velocity through the column. This reduction is carried out in the ratio of the cross sectional areas (or internal diameters) of the two columns. Eor example, if a 7.5-mm i.d. column operates at 1.0 ml/min, then in order to maintain the same linear velocity through a 4.6-mm i.d. column the flow rate would be... 

Often, the retention time is used but, as discussed above in Section 2.3, this absolute parameter changes with column length and flow rate and this precludes the use of reference data obtained in other laboratories. To make use of these reference data, the capacity factor (k ), which removes such variability, must be employed. 

The separation nuaber is the only column efficiency par2uaeter that can be deterained under teaperature progr2uued conditions [45,46]. The critical parameters that aust be standardized to obtain reproducible SM values for coluans of different length are the carrier gas flow rate and the temperature program. The SN is widely used as part of a standardized test method to evaluate the quality of open tubular columns for gas chromatography (section 2.4.3). 

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