Relative plating efficiency

The viability tests consisted of the establishment of the relative plating efficiency (RPE) and subsequently, the 50% lethal concentration LCjo (or RPE50) by using the colonyforming method on human epithelial cells in culture, the LI 32 cell-line. This test measures quantitatively only one criterion of toxicity which is cell death or cell survival, and consequently is specific, liable, and easily reproducible. It makes possible the ranking of cytotoxic effects of any chemical substance by comparison with the LC50 (Puck and Marcus 1955 Frazier and Andrews... 

FIGURE 2. Relative plating efficiency of MIT-2 lymphoblasts in 6TG. Cells were plated in soft agar with Lesch-Nyhan feeder layers at the indicated 6TG concentrations. (O) Wild-type ( ) HGPRT" mutants. The plateau in the wild-type survival curve represents the mutant fraction in that culture. 

EmpiricalEfficieny Prediction Methods. Numerous empirical methods for predicting plate efficiency have been proposed. Probably the most widely used method correlates overall column efficiency as a function of feed viscosity and relative volatiHty (64). A statistical correlation of efficiency and system variables has been developed from numerous plate efficiency data (65). 

Mass-transfer theory indicates that for trays of a given design the factors most hkely to inflnence E in absorption and stripping towers are the physical properties of the flnids and the dimensionless ratio Systems in which the mass transfer is gas-film-controlled may be expected to have plate efficiencies as high as 50 to 100 percent, whereas plate efficiencies as low as 1 percent have been reported for the absorption of gases of low sohibility (large m) into solvents of relatively high viscosity. 

The literature is less extensive on the use of protoplasts in stress-tolerance investigations however, some applications have been attempted. For example, in one study protoplasts were isolated from the leaves of a wild relative of tomato shown to be salt tolerant and from a salt-sensitive, cultivated species (Rosen Tal, 1981). In the presence of NaCI the plating efficiency (number of surviving cells/number of cells applied to the plate) of the wild relative was greater than the cultivated, sensitive cultivar. Proline, when added to the culture media, was found to enhance the plating efficiency of the salt-sensitive cultivar but not the wild, salt-tolerant relative. These results suggest that traits related to salt tolerance are expressed by the isolated protoplasts and that the response of protoplasts to environmental stress can be manipulated, i.e. the proline response. 

LIQUID RESISTANCE TO INTERPHASE MASS TRANSFER. Liquid viscosity, gas solubility in absorbers, and relative volatility in rectification columns are important factors in determining the liquid resistance to interphase mass transfer. Increase in liquid viscosity, decrease in gas solubility for absorbers, and increase in relative volatility for rectification columns cause an increase in the liquid resistance to interphase mass transfer and a resultant reduction in plate efficiency. The ratio of the liquid rate to the gas rate influences the relative importance of the liquid resistance to interphase mass transfer. An increase in the ratio of liquid rate to gas rate reduces the importance of the liquid resistance and can cause an increase in the plate efficiency. 

While extremely large numbers of theoretical plates are possible with larger diameter columns (22, 23), calculations from chromatographic theory of the Internal diameters and column lengths necessary to achieve relatively high efficiencies in reasonable analysis times Indicate that column diameters of 50 to 100 ym l.d. are necessary for high-resolution SFC (23). For example, more than 10 effective theoretical plates are possible In less than two hours on 30-m long columns of 50 ym l.d. 

The plate luminescence efficiency is the ratio between the plate efficiency and the relative solar absorption. 

Era, Murphree plate efficiency, gas i> Relative froth density -/- -/-... 

By definitioii the Fenske equation for the minimum plate number only applies for plate columns with a plate efficiency of unity. The use of this equation for packed columns leads to considerable errors, especially at high relative volatilities. The minimum plate number of packed columns shoul be calculated with Equation 2.3.2-28 ... 

The relatively high plating efficiency (10-20%) of cells from recently initiated embryonal cultures facilitates clonal isolations prior to the third subcultivation. Some seven to nine different fibroblast-like forms can be isolated as clonal sublines from normal parent cultures, the number of cell phenotypes being higher for polyoma-treated cultures because of additional transformed epithelioid cell types. 

A better estimate of overall plate efficiency can be made with the Lockett and Leggett version of the empirical O Connell correlation, as shown in Figure 14.3. In this plot, the overall plate efficiency depends on the product of the average liquid-phase viscosity in cP and a dimensionless volatility factor. For distillation, the volatility factor is the average relative volatility between the light and heavy key components, aLK,HK- For absorbers and strippers, the volatility factor is 10 times the average AT-value of the key component. If an even better estimate of the plate efficiency is desired, and in particular one that depends on plate location and component, a semitheoretical method developed by Chan and Fair (1984a), based on the... 

Another approach in taxoid preparative separation included solid-phase extraction (alumina, silica, or RP-8 cartridges) followed by preparative TLC on silica gel plates with quaternary mobile phase consisting of dichloromethane-dioxane-acetone-methanol (83 5 10 2, v/v). In this way, 10-DAB III, paclitaxel, and cephalomannine as well as two further taxoids could be easily isolated with relatively high efficiencies from yew materials (Fig. 2). Multiple development technique or fiuther separation of the isolated taxoid fractions (especially less polar ones) on RP-2 silica bond stationary phase with methanol-water mixtures as mobile phases was applied for purification of the compounds isolated. 10-DAB III isolated in this way was relatively pure, as was shown in reversed-phase (RP)-HPLC analysis (Fig. 3). 

A correlation similar to that of Drickamer and Bradford was developed by O Connell (Ref. 26), but in this cash the plate efficiency was plotted as a function of ay. a = relative volatility) for fractionating towers and of y/HP or KeMy/d for absorption towers. These correlations include both of the main factors, solubility and liquid viscosity, found to be important by Walter and Sherwood. The inclusion of the solubility factor directly with the viscosity is probably not so sound as the type of grouping used in Eq. (17-13). It would be expected that O ConnelFs correlation would break down for extreme or unusual variations in the solubility factor. 

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