Secondary parameters

VGB standard also includes upper limits of lug/kg for carbon dioxide and 5ug/kg for chemical oxygen demand. Secondary parameter. 

Here we will not discuss these problems and the intriguing observation that am and strong correlation which is, however, difficult to explain (reviews Charton, 1981 Cook et al., 1989 Hansch et al., 1991). These questions were intensively studied in the 1970s and 1980s, leading gradually to the development of field and resonance parameters denoted by F and R respectively (after an original proposal of Swain and Lupton, 1968), which can be considered as independent of each other. The secondary parameters R + and R reflect the potential for an additional mesomeric donor-acceptor interaction (as in 7.7, and the opposite type with a donor instead of NQ2 and the reaction site as acceptor). 

Usually these secondary parameters can be determined from the primary blast wave parameters as discussed below. 

Accelerated testing depends critically on selecting a parameter whose effect on service life is so well understood that long lifetimes at low values of the parameter can be predicted from shorter lifetimes at higher values. The parameter may be the prime cause of degradation, such as in a stress-rupture test where longer lifetimes at lower loads are predicted by extrapolation from short lifetimes at higher loads. It can also be a secondary parameter, such as when temperature is increased to accelerate chemical attack while the principal factor, chemical concentration, is kept constant. This is because there is more confidence in the relation between rate of reaction and temperature than in the relation of rate of reaction to concentration. It is clearly essential that extrapolation rules from the test conditions to those of service are known and have been verified, such that they can be used with confidence. 

Table 4.3 CNV97100 transport parameter estimated in whole small intestine, duodenum and ileum. Fits were performed simultaneously using Eqs. (26)-(29). No inhibitor was present. S.E. - standard error, CV % - coefficient of variation. Vmjotai maximal velocity in whole small intestine, VmQ maximal velocity in duodenum, Vmj maximal velocity in jejunum, Vmj maximal velocity in ileum. Vmo, Vmj, and Vmjotaj are secondary parameters computed from (CV % is the same).

In this approach, the primary kinetic parameter is Vmj, whereas Vm[>, Vmj, and VmTotal are calculated as secondary parameters from Vm. ... 

The parameters that may be used for optimizing the selectivity in various chromatographic techniques may be referred to as secondary parameters. They will be discussed in chapter 3 and summarized in table 3.10. 

Table 3.10 summarizes the parameters of interest for the various chromatographic techniques described in this chapter. A distinction is made between primary and secondary parameters. 

Secondary parameters may affect retention, but always affect selectivity. In fact, ideally the parameters should be selected such that the retention (k) is kept roughly constant (i.e. in the optimum range) while the selectivity (a) can be varied. If the secondary parameters do affect retention, then sometimes this ideal situation can be approached by the simultaneous variation of two (or more) parameters at the same time. Examples of this may be found in chapter 5. 

The most common secondary parameter is the kind of stationary phase used, which is obviously a discrete parameter. Because the capacity factors will usually differ on different phases, several parameters will have to be varied at the same time. For example, if another stationary phase is chosen, the temperature may be adapted to bring the capacity factors back into the optimum range. 

A series of secondary parameters may be exploited. Changing the nature of the organic modifier is the most common and probably the most rewarding parameter to use. If ternary and quaternary mobile phases are considered, then the ratio between the concentrations of different modifiers becomes a continuous parameter that may be optimized. 

Table 3.10d lists the parameters for LSC. Again, most separations may be optimized by optimizing the eluotropic strength (primary parameter) and the nature (secondary parameter) of the mobile phase. The latter parameter involves the preparation of different iso-eluotropic mixtures containing different solvents, or small quantities of very polar components ( modulators ). As in the case of RPLC, there are several additional parameters that are not frequently exploited. 

Table 3.10f lists the most relevant parameters for ion-pairing chromatography (IPC). Here there are four major primary parameters, which cannot be seen as independent. Hence (see section 5.1.1), these four parameters should preferably be optimized simultaneously. Sensible upper and lower limits may be set for each of the parameters and an optimized separation may result from the process. If this is not the case, there arestill many secondary parameters that could be exploited. 

Finally, table 3.10g shows the relevant parameters for SFC. The density of the mobile phase (determined by the combination of pressure and temperature) is the main parameter for this technique. Several possible secondary parameters are listed in the table. Because SFC is not yet a mature technique, the list of secondary parameters may still undergo some changes. 

The second aspect of optimization in programmed analysis involves adapting the selectivity by variation of secondary parameters. The various secondary parameters listed in table 3.10 may be used to vary the selectivity of a chromatographic system without affecting retention to a great extent (see the discussion in section 3.6.1). 

If the program is optimized so that all sample components are eluted under optimal conditions, then other (secondary) parameters may be used for the optimization of the selectivity. However, changes in the secondary parameters may imply that the parameters of the program need to be re-optimized. For example, if the selectivity in a temperature programmed GC analysis is insufficient, then another stationary phase may be used to enhance the separation. However, the optimum program parameters obtained with one stationary phase cannot be transferred to another column that contains another stationary phase. The re-optimization of the temperature program for the other column will require at least one additional experiment to be performed. 

The primary and secondary parameters that may be used for the optimization of the program and the selectivity in programmed analysis, respectively, are listed in table 6.3 for the various chromatographic techniques. 

In programmed solvent LC the nature of the modifier(s) in the mobile phase is the most common secondary parameter that may be used for the optimization of the selectivity. This is an attractive parameter, because different modifiers may be selected and programmed automatically on various commercial instruments. Therefore, the possibilities for selectivi-... 

Parameters for the optimization of programmed analyses in various chromatographic techniques. Primary parameters may be used to optimize the program parameters (initial and final conditions, slope and shape). Secondary parameters may be used to optimize the selectivity. 

Method Primary parameter(s) (program) Secondary parameter(s) (selectivity)... 

The most useful secondary parameter for the optimization of the selectivity in programmed solvent LC is the nature of the modifter(s) in the mobile phase. The selectivity can be varied by selecting various solvents (pure solvents for binary or ternary gradients mixed solvents for pseudo-binary gradients). Analogous to the situation in isocratic LC, it is possible to use different modifiers (and hence to obtain different selectivity) while optimum retention conditions are maintained for all solutes. This possibility to optimize the selectivity in programmed solvent LC will be discussed below. 

Of course, the simultaneous optimization of different (primary) program parameters (initial and final composition, slope and shape of the gradient) and secondary parameters (nature and relative concentration of modifiers) may involve too many parameters, so that an excessive number of experiments will be required to locate the optimum. This problem may be solved by a separate optimization of the program (primary parameters) and the selectivity (secondary parameters) based on the concept of iso-eluotropic mixtures (see section 3.2.2). This will be demonstrated below (section 6.3.2.2). However, the transfer of... 

Advantages are that the selectivity is optimized (secondary parameters) so that optimum resolution can be obtained and that all components of the sample are considered in the optimization procedure. Unlike the result of the gradient optimization procedure suggested by Jandera and Churafcek, (section 6.3.2.2) the lowest value for the resolution in the chromatogram is maximized and not the resolution of an arbitrary pair of solutes. 

A second reason not to become involved in extensive calculations for the complete mathematical optimization of the (primary) program parameters is that a more powerful way to optimize the separation of all sample components in the mixture may be to optimize the selectivity of the gradient by varying the nature of the mobile phase components (secondary parameters). 

No significant effect of either period or sequence was found for the primary parameter A1 IC0, and for the secondary parameters Cmax and tm z- Treatment effect was highly significant for all three PK parameters and subject effect was significant for AUCo-co, and ti/2xz but not for Cmax. 

In addition, there are in this class the three following secondary parameters ... 

Primary Parameters Secondary Parameters Popular Terms... 

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