Plates per second

We first note the very large differences in column performance for the two methods. Effective plates per second represents the speed characteristics of a column (e.g., the number of plates that can be generated in a given time interval) (13). As can be seen, HPLC is 100 to 1000 times faster than classTcal LC. (We shall discuss the differences between PLB and PB in the next section.) This improved performance arises mainly from the use of significantly smaller particle sizes in HPLC. Moreover, in classical LC, the mobile phase is delivered to the column by gravity feed, hence, the very low mobile phase velocities. In HPLC, it is desireable to improve performance... 

Plate number, 3,4,7, 27, 52, S3 Plates per second, 30-33 PLB, see Porous layer beads Polar group selectivity, 181-183 Polar solvent, selective uptake from eluent by polar adsorbent, 8S Polarizability, 206... 

At the other end of curve 1 in Fig. 10, we see that we ould generate 50 plates per second using 1.9-p.m particles at a pressure gradient of 31.5 atm/cm. The analysis time is now 100 sec, the column length 2.85 cm, and the pressure 90 atm. Such column inlet pressure is fairly easy to use and the analysis time is quite attractive. On the other hapd the column is somewhat short and it is difficult to make a column With a length of 2.83 0.05 cm. The most difficult task, however, wolttd be to prepare... 

Reducing chromatographic media particle size allows the number of theoretical plates per second to be increased. However, due to the resolution... 

This is known as the plate time and has units of seconds. It is equivalent to the amount of time it takes to generate one theoretical plate. Its inverse would be plates per second, N/to. Plates per second may also be expressed more generally as N/t for elution times other than the void time [2,3]. These terms more effectively describe the criteria of resolution per unit time that are desired to be maximized (actually, N/t is proportional to resolution squared per time) unfortunately, they are not widely used in the literature, and for the sake of continuity will not be used in this discussion. The following sections will look at what influences plate height and velocity and how best to minimize H/u. 

Resolution and analysis time being interrelated,. effective plates per second, is sometimes a better criterion for comparing column performance. 

C — Carbowax, FFAP — free fatty add phase, DMA — 2,6-dimethylaniline, DMF — 2,6-dimethylphenol, df — average liquid film thickness, N/s — number of theoretical plates per second, UT — utiliz theoretical efficiency. 

Sodium anthraquinone-p-sulphonate ( silver salt ). Place 60 g. of fuming sulphuric acid (40-50 per cent. SO3) in a 250 or 500 ml. round-bottomed flask and add 50 g. of dry, finely-powdered anthra-quinone (Section IV,145). Fit an air condenser to the flask and heat the mixture slowly in an oil bath, with occasional shaking, so that at the end of 1 hour the temperature has reached 160°. Allow to cool and pour the warm mixture carefully into a 2 litre beaker containing 500 g. of crushed ice. Boil for about 15 minutes and filter off the unchanged anthraquinone at the pump. Neutralise the hot filtrate with sodium hydroxide and allow to cool, when the greater part of the sodium anthra-quinone-p-sulphonate separates as silvery glistening plates ( silver salt ). Filter these with suction and dry upon filter paper or upon a porous plate. A second crop of crystals may be isolated by concentration of the trate to half the original volume. The yield is 40-45 g. 

The strength of the ion current relates to the number of ions per second arriving at the collector plate, and a mass spectrum can be regarded as a snapshot of the current taken over a definite period of time. Because of the finite time taken to produce a mass spectrum, it is a record of the abundances of ions (often mistakenly called intensities of ions). 

Flame plating (D-gun) employs oxygen and fuel gas. In this method, developed by the Union Carbide Corporation, the gas mixture is detonated by an electric spark at four detonations per second. The powders, mixed with the gas, are fed under control into a chamber from which they are ejected when detonation occurs. The molten, 14—16-pm particles are sprayed at a velocity of 732 m/s at distances of 5.1—10.2 cm from the surface. The substrate is moved past the stationary gun. 

FIG. 14-41 plate efficiencies, ethanol-water. To convert (feet per second) (pounds per ciihic foot) " to (meters per second) (kilograms per ciihic meter) " , multiply hy 1.2199. (Kiischhaum, Destilher-Rektifiziertechnik, 4th ed., Sptinger-Verlag, Berlin and Heidelherg, 1969.)... 

FIG. 14-118 Aerodynamic cut diameter for a single-sieve-plate scrubber as a function of bole size, bole-gas velocity, and froth density, F, g/cm. To convert meters per second to feet per second, multiply by 3.281 to convert grams per cubic centimeter to pounds per cubic foot, multiply by 62.43. [Calveti, J. Air Pollut. Control Assoc., 24, 929 (1974).]... 

Typical velocities in plate heat exchangers for waterlike fluids in turbulent flow are 0.3-0.9 meters per second (m/s) but true velocities in certain regions will be higher by a factor of up to 4 due to the effect of the corrugations. All heat transfer and pressure drop relationships are, however, based on either a velocity calculated from the average plate gap or on the flow rate per passage. 

Another approximation to planar Couette conditions can be found in the cone-and-plate cell, shown in Figure 2.8.3. The angular speed of rotation of the cone is taken to be Q (in radians per second) while the angle of the cone is a (in radians) and is generally small, say 4-8°. A point in the fluid is defined by spherical polar (r, 0, ()>), cylindrical polar (q, z, cj)) or Cartesian (%, y, z) coordinates, where Q = y = rsin0 and z = rcos0. 

A slurry of CaC03 in water at 25°C containing 20% solids by weight is to be filtered in a plate-and-frame filter. The slurry and filter medium are tested in a constant pressure lab filter that has an area of 0.0439 m2, at a pressure drop of 338 kPa. It is found that 10 3m3 of filtrate is collected after 9.5 s, and 5 x 10 3 m3 is collected after 107.3 s. The plate and frame filter has 20 frames, with 0.873 m2 of filter medium per frame, and operates at a constant flow rate of 0.00462 m3 of slurry per second. The filter is operated until the pressure drop... 

The tangential velocity component ve varies linearly from zero at the lower plate to the speed of the cone at the cone s surface. At a radial distance r, the cone s tangential speed is fir where Cl is in radians per second. At this location the height of the gap is ar where a is the angle of the gap in radians. Thus, the shear rate y is given by... 

We might want to increase a> to generate larger limiting currents in order to increase the precision. Improving the precision by this means is valid at low to medium rotation rates (that is, up to about 100 cycles per second) because the motion of solution over the face of the electrode is smooth and reproducible. We say that the flow is laminar. (The word laminar comes from the Latin root lami, meaning thin layer or plate .) We can then see how laminar flow implies that solution readily flows over itself in a smooth and reproducible way. 

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