Sampling volume flow rate

Sampling volume flow rate The induced flow rate into a sampling system. 

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),... 

To optimize the method, a set of experiments were performed in which the influence of the ABTS radical cation/carrier ratio, sample volume, flow rate, and mixing coil... 

It follows from equation (2) that the sample load will increase as the square of the column radius and thus the column radius is the major factor that controls productivity. Unfortunately, increasing the column radius will also increase the volume flow rate and thus the consumption of solvent. However, both the sample load and the mobile phase flow rate increases as the square of the radius, and so the solvent consumption per unit mass of product will remain the same. 

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-... 

Similar considerations apply to best volume flow rates for samples of different molar mass. For high molar mass samples, flow rates should be reduced to avoid shearing the macromolecule in the column. Moreover, a reduced flow rate is necessary because the diffusion coefficients of large molecules will get pretty small. This means that the macromolecule will pass by a pore in the packing material without having the time to enter it, if the linear flow rate is too high. 

The problems associated with coupling packed columns to a mass spectrometer are s re severe than those encountered with capillary columns. Conventional pacdced columns are operated at much higher flow rates, 20 to 60 al/ain, and although this diminishes the influence of dead volumes in the interface on sample resolution, it poses a problem due to the pressure and volume flow rate restrictions of the mass spectrometer. The interface must provide a pressure drop between column and mass spectrometer source on the order of 10 to 10, it must reduce the volumetric flow of gas into the mass spectrometer without diminishing the mass flow of sample by the same amount, and it must retain the integrity of the sample eluting from the column in terms of the separation obtained and its chemical constitution [3,25,26]. To meet the above requirements the interface must function as a molecular separator. 

Rate Meter Measures the instantaneous volume flow rate through the sampling systems. An example would be a rotameter or venturi meter. Used to set precise flow rate for flow sensitive sampling devices. 

In an effort to improve the accuracy of the determination of the end-point, the triangle-programmed titration was devised [97]. The sample with concentration Cx flows at a constant rate of Wj. The titrant is introduced at programmed volume flow-rate Ir, the change in Fr following the pattern of an isosceles triangle (fig. 5.13a). The time of the whole program is 2t, for tr, Ir =(2r—r)n n and t are constants. The maximum titrant mass flow should exceed the sample mass flow (= c w ). Two connected titration curves are obtained (fig. 5.13h), the time elapsed between the two equivalence points for the titration reaction... 

Side processes may bring about either an increase or a decrease in measured retention volumes. Often, the presence of side processes in the SEC system is signalized by the increased dependence of polymer retention volumes on the operational parameters such as the sample concentration, flow rate, and temperature. 

Commonly, silica particles occupy —40% of the column volume and solvent occupies —60% of the column volume, regardless of particle size. The column in Figure 25-2a has an inside diameter of 4.6 mm and was run at a volume flow rate, uy, of 3.0 mL/min with a sample size of 20 p.L. The column in Figure 25-2b has a diameter of de = 2.1 mm. What flow rate should be used in trace b to achieve the same linear velocity, wx, as in trace a What sample volume should be injected ... 

Suppose that you have optimized a gradient on a 0.46 X 25 cm column and you want to transfer it to a 0.21 X 10 cm column. The quotient V2/V is ( nr2L)2/( nr1L), where r is column radius and L is column length. For these columns, V2/Vj = 0.083. Equation 25-8 tells us to decrease the volume flow rate, the sample mass, and the delay time to 0.083 times the values used for the large column. The gradient time should not be changed. 

Experimental Procedure. Gas flow was initially fed to a column approximately 2/3 full of slurry. After the gas flow rate was set, the slurry flow was started and adjusted using the calibrated volume. Flow rates were held constant during the runs, which lasted 1+5 to 75 minutes for the 12.7 cm column, and 180 minutes for the 30.5 cm column. At the end of this time, slurry samples were taken, starting at the top of the column and working down, so as not to disturb upstream conditions. All slurry ports were purged before taking a sample, and stopcocks were turned quickly to full open and full closed to prevent settling of slurry within the sample line. 

When the diluted sample of solute is injected during rotation, it is concentrated at the beginning of the channel, due to the fact that the average volume flow rate of the retained solute is lower than the average flow rate of the injected solution. Hence diluted colloidal samples can be concentrated by sedimentation-FFF [189]. One can even operate such that the injection is run at a higher field force and, after the entire sample solution is injected, the field force is decreased to the required value. 

Hinde and Lloyd [27] are more interested in extracting samples for continuous on-line analysis. They state that the process streams from industrial wet classifiers can vary in volume flow rate, solids concentration and particle size distribution. Any sampling technique should be able of coping with these variations without affecting the representativeness of the extracted sample. 

Another critical factor can be, in fact, the size of the sample. The flow rates used in this technique are usually very low, between 1 and 10 /Al/min, and recently ultraslow flow rates (less than 0.3 /il/min) [68] have also been proposed in order to increase the recovery of a selected analyte. This approach results in very small sample volumes (a few microlitres) often with a very low analyte concentration. At this level, evaporation is also a problem to be considered. To obtain larger samples, both the collection time and/or the flow rate can be increased, but in this case, the temporal resolution and the recovery will also decrease. The analytical techniques used in the analysis of the dialysate hence have to be adequate for these volumes and concentrations, and very sensitive detection systems have been developed. 

The testing system (Fig. 1) was a 1.2 volume pressure apparatus made of metaplex (1). The har support covered with the membrane (2) of an effective surface area of 49.2 cm was fixed in the lower part of the apparatus. To maintain the dye concentration on the level required, continuous circulation of the permeate between the feeding tank (5) and the apparatus was applied. The solution was mixed with a magnetic stirrer (3) which prevents excess concentration of dye on the membrane surface. Pressure was generated by feeding the apparatus with an inert gas (nitrogen) from a cylinder (8). Samples for flow rate measurements and determinations of dye concentration in the permeate were taken through a stub pipe (4). 

With liquid samples, Xhe flow-rate strongly influences the pervaporation process. The lower the flow-rate is, the longer will be the residence time in the donor chamber of a given volume of sample and the closer to equilibrium will be the analyte mass transfer. The flow can be stopped when the sample is in the donor chamber to allow steady-state mass transfer. This situation is not desirable because it lengthens the separation unduly. Instead, a fresh sample can be passed through the donor chamber as often as required provided the volume of sample available is not limited. 

Figures 18.38 and 18.39 show how the mobile phase composition and flow rate can be optimized experimentally to increase the production rate of a purified component at a given purity [72]. Increasing the concentration of the strong solvent in the mobile phase permits a decrease of the retention time (at constant a in the particular case), and in the same time a significant increase in the recovery yield at constant sample size, as illustrated in Figure 18.37, in agreement with the theoretical results reported earlier (see Figure 18.11). Figure 18.38 shows that increasing the volume flow rate threefold permits a threefold increase in the production rate at constant feed load and recovery yield.

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