Flow rate column scaling

Transferring a method from a standard 4.6-mm I.D. column to one of narrower diameter can cause loss of resolution due to extracolumn contributions to peak broadening. As column diameter and flow rate are scaled down, the peak... 

Rohrschneider [205,210] has developed a scheme for the characterization of stationary phases for gas chromatography. The scheme is based on the retention index (/). The retention index is a dimensionless retention parameter, designed to be independent of flow rate, column dimensions and phase ratio. The retention index of a solute is defined as 100 times the number of carbon atoms in a hypothetical n-alkane, which shows the same net retention time as that solute. This definition is illustrated in figure 2.2. By plotting the logarithm of the net retention time against the number of carbon atoms in n-alkanes, a straight line is obtained. The net retention time for a solute may then be located on the vertical axis, and the retention index found on a horizontal scale, which represents 100 times the scale for na... 

Using SEC, most accomplishments of the commonly used RP-LC technique can be employed, such as various detector options, high sample loading capacity, variability in stationary phases and up-scaling option. Often in SEC, non-size-exclusion effects such as electrostatic and hydrophobic interactions between the analyte and stationary phase may be observed. The separation efficiency can be improved by optimizing the mobile phase, flow rate, column length, and sample volume. Practical guidelines for SEC method development have been described [42]. 

When changing the dimensions of the column, the method should be scaled geometrically to maintain equivalency. The flow rate is scaled to maintain the same linear velocity as the original method. This is done based on the ratio of the column diameters squared ... 

Up to sixteen separate samples can be loaded on to the carousel and their chromatographic characteristics (flow rate, sensitivity, scale factor, delay time before injection, run time and number of injections up to a maximum of 9), separately loaded into the microprocessor for automatic analyses. The instrument has three compartments which are separately thermostatted-pump, injector and column compartments. The upper temperature is 150°C. The temperature of the compartments are controlled by proportional heaters allowing slow heating and cooling rates to be adopted if required. This minimizes thermal shock to the gel columns and also overheating—two features which help to prolong the life of the columns. 

NOTE To develop reasonably good data for scale-up to full plant design, it is important to have the operation of the pilot column system as near as possible to the anticipated plant conditions. The most critical factors, flow rate and feed impurity concentration, must be constant for the entire test run. 

PSS SEC column dimensions were chosen to allow easy scaling of chromatography conditions without the need to optimize separations for each column dimension separately. The volume flow rate and the sample load can be calcu-... 

Fig. 4.1.6 HPLC analysis of a sample of purified natural aequorin on a TSK DEAE-5PW column (0.75 x 7.5 cm) eluted with 10 mM MOPS, pH 7.1, containing 2mM EDTA and sodium acetate. The concentration of sodium acetate was increased linearly from 0.25 M to 0.34 M in 14 min after the injection of the sample. Full-scale 0.02 A. Flow rate 1 ml/min. Reproduced with permission, from Shimomura, 1986a. the Biochemical Society.

Figure 4. GPC chromatograms of commercial soya lecithin (solvent THF columns 2 X G2000H Toyo Soda flow rate 1.96 mL/min injection 50 pJL X 75 mg/mL (---------------) 254 nm detection, 0.2 abs. units full-scale)...

Detection requirements in preparative-scale chromatography also differ from analytical erations where detectors are selected for their sensitivity. Sensitivity is not of overriding importance in preparative-scale chromatography the ability to accommodate large column flow rates and a wide linear response range are more useful. The sensitivity of the refractive index detector is usually quite adequate for prqtaratlve work but the ... 

FIGURE 3.4 Calculated peak capacities dependent on flow rate and gradient time. Left conventional column using 5-flm particles. Middle same column dimension with sub-2-micron particles (1.8 flm). Right sub-2 -micron particles in column with same L/dp ratio as conventional column on left. Parameters for typical applications have been estimated. Note logarithmic scale of flow rate and time axis. 

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