Column operation flow rate

Using other methods for the calculation of plate count can result in different numbers, depending on peak shape. It should also be kept in mind that many other operational parameters, such as eluent viscosity, column temperature, flow rate, and injection volume, will influence the results of the plate count determination. 

Each SynChropak column is tested chromatographically to assure that it has been packed according to specifications. For SynChropak GPC columns, a mixture of a high molecular weight DNA and glycyltyrosine, a dipeptide, is used to evaluate internal volume and efficiency. The mobile phase used for the test is 0.1 M potassium phosphate, pH 7, and the flow rate is 0.5 ml/min for 4.6-mm i.d. columns. Minimum plate count values and operational flow rates are listed in Table 10.4 for 4.6-mm i.d. columns of all supports and the various diameters of the SynChropak GPC 100 columns. 

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... 

This can potentially be overcome by the use of microbore HPLC columns with flow rates which are directly compatible with mass spectrometer operation, although the necessary decrease in injection volume results in little overall gain in the concentration of sample reaching the mass spectrometer. In addition, at the time that the DLI was available, the use of microbore HPLC, which introduces another set of potential problems related to chromatographic performance, was probably as widespread as the use of LC-MS It has been assessed [2] that in around 25% of the reported applications of DLI, microbore HPLC has been utilized. 

At this point it is worth considering the demands made on the instrumentation for operation with wide bore columns and, in particular, the adaptation of analytical Instruments for this purpose [596,597]. The pump requirements for preparative separations differ from those in analytical HPLC as the ability to generate high flow rates at moderate backpressures is crucial to the efficient operation of wide bore columns. A flow rate maximum of 100 ml/min with a pressure limit of 3000 p.s.i. is considered... 

Figure 4 shows breakthrough profiles during the adsorption operation of Pb(II) by both FPS-f and FP-f packed columns. Surprisingly, both columns gave flow rate independent breakthrough profiles of Pb(II), although the... 

When a specific feed composition is given, the constraints on m1 and m4 as well as the complete separation region in the (m2, m3) plane can be determined,since these depend only on the parameters of the adsorption equilibrium isotherms and the feed composition itself. Based on these values an operating point can be selected, i. e. a set of four values of = 1,..., 4 fulfilling the complete separation requirements. Since the flow rate ratios are dimensionless groups combining column volumes, flow rates and switching intervals, the constraints on the flow rate ratios are independent of the size and productivity of the SMB unit. 

Note that Vg is proportional to the square of the inner radius of the column. It is important to have a rough idea of the void volume of the column since it often dictates the operating flow-rate range, sampleloading capacity, and mass sensitivity (the minimum detectable amount) of the assay. For instance, a typical analytical column (150mm x 4.6mm i.d.) has a Vg of about 1.5 mL and is operated at 1.0mL/min. In contrast, by reducing the inner diameter to 2.0 mm, a typical LC/MS column (150mm X 2.0mm i.d.) has a Vg of about 0.3mL and is operated at... 

Tables 2 and 3 show an antibody purification process scale-up from laboratory scale (1 mL) to intermediate scale (500 mL) to large scale of 10-85 L column volumes, maintaining the column bed height constant. Product quality and biocontaminant levels were maintained throughout the scale-up, though operational flow rates were significantly changed, demonstrating the consistency of the overall purification process. Thorough analysis of each coliunn performance is essential in order to sustain the process robustness at different scales of operation.

When conparing tray designs the turndown ratio is inqjortant because it is a measure of the flexibihty of a column in dealing with a change in flow rate. The turndown ratio is defined as the ratio of the maximum to minimum operating flow rate. For bubble cap and valve trays, the turndown ratio is about ten whereas for sieve trays it is only about three. 

In summary, in order to reduce the total cost, the use of lower-price solvents is important. To minimize the impact of higher solvent cost on the total cost, the operating parameters are adjusted by using a longer column, lower flow rates and lower loadings. 

Later system configurations utilised this same idea but to facilitate a more useful option. This time the selection valve was used to vary the scale of preparative operation by connecting two different diameter preparative columns (e.g. 10 mm and 20 mm). By maintaining a maximum operating flow rate (in unattended mode) of 4.0 ml/min... 

LC operation No restrictions to mobile phase composition Gradient elution Volatile and nonvolatile additives (buffers, ion-pair reagents) Free choice of LC column dimensions Flow-rate between 1 pl/min and 2 ml/ntin... 

The actual process flow rates are important in nonequilibrium model simulations, whereas in most equilibrium stage simulations, a simulation with a feed flow rate of 1 unit is as meaningful as a simulation with a feed flow of 10, 100, or 573 units. In real columns the flow rates influence the mass transfer coefficients as well as the tray hydraulics. An inappropriate flow specification may mean the column will flood or, just as likely, dump all the liquid through the holes in the tray. Thus, it is important to ensure that the specified (or calculated) flows and tray or packing characteristics are consistent with the satisfactory operation of the column. 

A high pressure syringe pump operated under constant pressure mode Is often used for low flow rate operation In narrow-bore packed column HFLC. Flow rates as low as 0.05 Mi /nln can be obtained. The drawback of constant pressure operation Is the potential flow rate variation due to a flow resistance change In the column. 

Column dimensions—length (L) and column inner diameter (dc or i.d.)— control column performance (N, speed, sensitivity, sample capacity) and its operating characteristics (flow rate, back pressure). Designations of various column types based on column inner diameters and their associated characteristics are shown in Table 3.1. Note that void volume, sample capacity, and operating flow rate are proportional to (dc)2, while detection limit, or sensitivity, is inversely proportional to (dc)2. Note also that prep columns (>10mm i.d.), microbore (micro columns (<0.5 mm i.d.) will require specialized HPLC instruments (see Chapter 4). There is a definitive trend toward the increased use of shorter and smaller inner diameter analytical columns due to their higher sensitivity performance and lower solvent usage.9"11 This trend will be explored later. 

Fig. 12. HPLC-RC analysis of the metabolism of radiolabelled lAA conjugates by leaf discs from wild-type and RolB tobacco plants. After a 24 h metabolism period leaf discs were extracts with methanol and ca. 10 000 dpm aliquots were analysed by reverse phase HPLC-RC with column and flow rate, as in Fig. 6. Mobile phase 25 min, 10-60% gradient of methanol in 1% aqueous acetic acid. Detector radioactivity monitor operating in homogeneous mode [66,67]. Traces illustrate [ CJIAGluc metabolism by (A) wildBtype and (B) RolB leaf discs [ HJlAInos metabolism by (C) wildBtype and (D) RolB leaf discs [ C]IAAsp metabolism by (E) wildBtype and (F) RolB leaf discs [117],...

Solvent delivery modules are required to deliver a pulse free flow of eluant to the column at flow rates ranging from 0.1 to 10 ml min with a precision of 0.5% or better. The pump must be capable of operating at pressures up to 7000 psi (48.3 MPa) and the system should incorporate a degassing unit to remove dissolved air and other gases from the eluant. 

In addition, there are four degrees of freedom that are adjustable during design and are also adjustable during operation of the column reflux flow rate (/ ), vapor boilup (V), sidestream flow rate (5), and the liquid split ratio (jSl = i-p/i-R)- The variable Lp is the liquid flow rate fed to the prefractionator side of the wall, and Lp is the total liquid leaving the bottom tray in the rectifying section. Of course, the rest of the liquid coming from the bottom of the rectification section is fed to the sidestream side of the column. Distillate and bottoms flow rates are used to maintain liquid levels in the reflux drum and column base, respectively. 

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