Resolution conditions for

Many SEM studies involve magnifications below about lOOOOx where depth of field and minimum degradation are more important than resolution. Conditions for maximum depth of field are ... 

Figure 2.186 General resolution conditions for two mass signals —10% valley definition (Budzikiewicz, 2005).

Resolution The chromatographic separation of two components, A and B, under trace conditions with small feed injections can be characterized in terms of the resolution, R,. For nearly Gaussian peaks ... 

In order to select the instmmental conditions for carrying out the ATR measurements several parameters including the number of accumulated scans per spectra or nominal resolution were tested. To avoid the crosscontamination and to establish an appropriate strategy for cleaning the ATR cell between samples, several procedures were tested using background and blank controls. Moreover, the possible sample sedimentation on the ATR plate cell due to the complexity of the sample matrix during the spectra acquisition was also checked. 

Reiterating the conditions for a chromatographic separation once again, for two solutes to be resolved their peaks must be moved apart in the column and maintained sufficiently narrow for them to be eluted as discrete peaks. However, the criterion for two peaks to be resolved (usually defined as the resolution) is somewhat arbitrary and is usually defined as the ratio of the distance between the peak maxima to half the peak width (a) at the points of inflection. To illustrate the various degrees of resolution that can be obtained, the separation of a pair of solutes 2o, 3o, 4o, 5o and 6o apart are shown in Figure 12. Although, for baseline resolution, it is clear that the peak maxima should be separated by at least 6o for most quantitative analyses. 

However, any given column operated at a specific flow rate will exhibit a range of efficiencies depending on the nature and capacity ratio of the solute that is chosen for efficiency measurement. Consequently, under exceptional circumstances, the predicted conditions for the separation of the critical pair may not be suitable for another pair, and the complete resolution of all solutes may still not be obtained. 

The ionic species of the mobile phase will also affect the separation. This is shown in Table 4.3 by the difference in resolution values for magnesium chloride buffer compared to sodium sulfate buffer. In addition, calibration curves for proteins in potassium phosphate buffers are shallower than those generated in sodium phosphate buffers. The slope of the curve in Sorenson buffer (containing both Na and ) is midway between the slopes generated with either cation alone (1). Table 4.4 illustrates the impact of different buffer conditions on mass recovery for six sample proteins. In this case, the mass recovery of proteins (1,4) is higher with sodium or potassium phosphate buffers (pH 6.9) than with Tris-HCl buffers (pH 7.8). 

Such off-zone-centre, soft-mode systems offer the most favourable conditions for a test of the hypothesis that the central peak is a precursor to a Bragg reflection in the transformation phase. Zone-centre softening, such as occurs in NbaSn, results in the central mode scattering emerging from an existing Bragg peak, which ultimately splits in the lower symmetry transformation structure, which presents a problem with resolution. 

Fiq. 4. Conditions for resolution of two adjacent peaks on a desorption curve according to Carter (88). Tm and Tm are the temperatures at maximum desorption rate for the first and second peak, respectively. T and T are the temperatures at maximum desorption rate for the first and second peak, respectively. Te and Te are the temperatures at 1/e = 37 per cent of the maximum desorption rate for the first and second peak, respectively. 

Irimescu and Kato have recently described an interesting example of enzymatic KR in ionic liquids instead of organic solvents (Scheme 7.4) [12]. The resolution with CALB is based on the fact that the reaction equilibrium was shifted toward the amide synthesis by the removal of water under reduced pressure. Nonsolvent systems have been also employed in this enantioselective amidation processes, reacting racemic amines with aliphatic acids. The best reaction conditions for the conversion of acids to amides was observed using CALB at 90 °C under vacuum. Meanwhile, no... 

Sigman et al. have optimized their system too [45]. A study of different solvents showed that the best solvent was f-BuOH instead of 1,2-dichloroethane, which increased the conversion and the ee. To ensure that the best conditions were selected, several other reaction variables were evaluated. Reducing the catalyst loading to 2.5 mol % led to a slower conversion, and varying temperature from 50 °C to 70 °C had little effect on the selectivity factor s. Overall, the optimal conditions for this oxidative kinetic resolution were 5 mol % of Pd[(-)-sparteine]Cl2, 20 mol % of (-)-sparteine, 0.25 M alcohol in f-BuOH, molecular sieves (3 A) at 65 °C under a balloon pressure of O2. 

The most popnlar system is a reversed phase column (Cl8), on a silica base column. However, the use of C18 on a polymer-based column has been reported to provide better resolution, especially for the separation of complex anthocyanin mixtures containing acylated pigments. - Polymer-based columns also show better stability at low pH operating conditions. 

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