Columns flow rate through

A significant advantage of immobilized enzymes is the total absence of catalytic activity in the product. Moreover, the degree of substrate-to-product conversion can be controlled during processing, eg, by adjusting the flow rate through a packed-bed column reactor of immobilized enzyme. 

At high-flow rates through perforated plates such as those that occur in distillation columns, Calderbank and Rennie [Trans. In.stn. Chem. Engrs., 40, T3 (1962)] Porter et al. [ibid., 45, T265 (1967)] Rennie and Evans [Br. Chem. Eng, 7, 498 (1962)] and Valentin (op. cit.. Chap. 3) have investigated and discussed the effect of the flow conditions through the iTuutiple orifices on the froths and foams that occur above perforated plates. 

Since the vapour phase dynamics are negligible, the vapour flow rate through the column is constant from plate to plate, at the rate of V, k mol/s. The liquid flow rates Ln, and the liquid holdup on the plate, however, will vary, under changing hydrodynamic conditions in the column. The corresponding notation, for any plate n in the column, is as indicated in Fig. 3.58. 

Where Q, is the minimum detectable amount, R the detector noise level and s the detector sensitivity [135,146,151,152]. For a concentration sensitive detector the minimum detectable concentration is the product of Q, and the volumetric gas flow rate through the detector. The minimum detectable amount or concentration is proportional to the retention time, and therefore, directly proportional to the column radius for large values of n. it follows, then, that very small quantities can be detected on narrow-bore columns. 

The function of the pump in hplc is to pass mobile phase through the column at high pressure and at a controlled flow rate. One class of pump (constant pressure pump) does this by applying a constant pressure to the mobile phase the flow rate through the column is determined by the flow resistance of the column and any other restrictions between the pump and the detector outlet. Another type (constant flow pump), generates a given flow of liquid, so that the pressure developed depends on the flow resistance. 

Compared to syringe type or reciprocating pumps, pneumatic amplifier pumps are very cheap. They tend to be rather difficult to dismantle for repairs, and some types are very noisy in operation. Because they do not provide a constant flow of mobile phase, they are not used much in analytical hplc. They can, however, operate at high pressures and flow rates and so are used mainly for packing columns, where high pressures are needed and variations in the flow rate through the column do not matter. 

Figure 11(A) shows a principle sketch of a SEC set-up. The eluent (solvent) is pumped at a constant flow rate through the system. A small amount of polymer solution (typically 200 pL) is injected manually or with an autosampler. The main part comprises a set of columns (typically 3-4 columns+pre-column) typically packed with microporous styrene-divinylbenzene, porous glass, or silica. In the routine analytical laboratory it is especially useful to have a pre-column in order to collect impurities that might be present in the samples. If many different samples are to be analyzed, it is necessary to check the reliability of the columns frequently to avoid artefacts due to residues from previous samples still held on the column. In order to avoid problems, samples should be purified before they...

The pressure developed by a centrifugal pump depends on the fluid density, the diameter of the pump impeller, the rotational speed of the impeller, and the volumetric flow rate through the pump (centrifugal pumps are not recommended for highly viscous fluids, so viscosity is not commonly an important variable). Furthermore, the pressure developed by the pump is commonly expressed as the pump head, which is the height of a column of the fluid in the pump that exerts the same pressure as the pump pressure. 

Most of the chromatographic techniques described thus far are usually performed under relatively low pressures, where flow rates through the column are generated by low-pressure pumps (i.e. low-pressure... 

Columns are made from straight lengths of precision-bore stainless-steel tubing with a smooth internal finish. Typically they are 10-25 cm long and 4-5 mm i.d. Microbore columns, 20-50 cm long and with an i d. of 1-2 mm, are sometimes used where sample size is limited and to minimize solvent consumption because the volumetric flow rate through them is less than a... 

The //PLC system described in this chapter is equipped with 24 parallel columns for liquid chromatography, each with its own sample introduction port and exit port for connection to detectors of choice (UV absorbance and/ or fluorescence). Flow from a binary solvent delivery system is divided evenly across 24 channels and results in 1/24 of the programmed pump flow rate through each column (i.e., total flow of 300 /zL/ min will produce a flow of 12.5 /zL/ min in each column). Samples are introduced to the columns by a multichannel autosampler configured to sample from either 96-or 384-well SBS standard plates. Figure 6.2 depicts a general view of the system. 

FIGURE 14.9 Performance of short column ultrahigh pressure nano LC system at 10 /rL/min for the separation of tranylcypromine sulfate, perphenazine, and their impurities. Nano LC may be operated at 10 times optimum column flow rate and achieve ultrahigh throughput and reproducibility. Short column (3 cm x 150 /mi inner diameter) was packed with 1.8 /im C18 particles. Solvent A was water with 0.4% ammonia solvent B was acetonitrile with 0.4% ammonia. Gradient 0 to 1 min, 3 to 10% B 1 to 1.3 min, 10 to 35% B, 1.3 to 3.5 min, 35 to 90% B held at 90% B through 4.9 min and then returned to 3% B. Column head pressure was 7200 psi. 

For efficient separations it is essential to have very small and regularshaped support media, a supply of mobile phase pumped at a pressure that is adequate to give a suitable constant flow rate through the column and a convenient and efficient detection system. For all types of stationary phases the apparatus required consists of five basic components (Figure 3.5), each available with varying degrees of sophistication. 

For a constant flow rate through the column and using the concentration versus time relationship of Eq. (96), the integration yields the familiar exponential form... 

Hot oil from the base of a distillation column is used to reboil two other distillation columns that operate at lower temperatures. The design flow rates through reboilers I and 2 are 100 and 150 gpm, respectively. At these flow rates, the pressure drops through the reboilers are 20 and 30 psi. The hot oil pump has a flat pump curve. 

---