Resolution value

Typical mass resolution values measured on the LIMA 2A range from 250 to 750 at a mass-to-charge ratio M/ Z= 100. The parameter that appears to have the most influence on the measured mass resolving power is the duration of the ionization event, which may be longer than the duration of the laser pulse (5—10 ns), along with probable time broadening effects associated with the l6-ns time resolution of the transient recorder. ... 

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). 

Fig. 3-3. Comparison of the values of enantiomeric resolution of different DNP-D,L-amino acids at different deconvolution stages of a cyclic hexapeptide sublibrary. Resolution values in a cyclo(Arg-Lys-X-X-X-P-Ala) sublibrary, in the first line, are compared to those obtained in sublibraries with a progressively increasing number of defined positions. All the sublibraries were 30 mM in the running buffer while the completely defined cyclo(Arg-Lys-Tyr-P-Tyr-P-Ala) peptide is used at 10 mM concentration. Conditions cyclopeptide sublibrary in 20 mM sodium phosphate buffer, pH 7.0 capillary, 50 pm i.d., 65 cm total length, 57 cm to the window V = -20 kV, I = 40 electrokinetic injection, -10 kV, 3 s detection at 340 nm. (Reprinted with permission from ref. [75]. Copyright 1998, American Chemical Society.)...

The irradiating X-ray beam cannot be focussed upon and scanned across the specimen surface as is possible with an electron beam. Practical methods of small-spot XPS imaging rely on restriction of the source size or the analysed area. By using a focussing crystal monochromator for the X-rays, beam sizes of less than 10 pm may be achieved. This must in turn correspond with the acceptance area and alignment on the sample of the electron spectrometer, which involves the use of an electron lens of low aberration. The practically achievable spatial resolution is rarely better than 100 pm. A spatial resolution value of 200 pm might be regarded as typical, and it must also be remembered that areas of up to several millimetres in diameter can readily be analysed. 

Basic electronic circuits employed in the sensor area will be discussed with a particular emphasis on the noise aspects, which are important for achieving high resolution values in those contexts where measurement of the lowest concentration values of chemicals is the main objective. 

All the changes in I and A should be done in order to have negligible self-heating of the thermistor, and an amplifier must be selected having a noise as low as possible in order to obtain an optimal resolution value for the determination of small temperature changes. 

The resonator is usually made of quartz and both longitudinal and shear modes can be used. As to the quartz, crystallographic cuts showing a highly stable temperature operation dependence are carefully selected in order to improve the possibility of obtaining satisfactory resolution values. 

Eq. 17.42 is the expression of the resolution for CE in electrophoretic terms. However, the application of this expression for the calculation of Rs in practice is limited because of D,. The diffusion coefficient of different compounds in different media is not always available. Therefore, the resolution is frequently calculated with an expression that employs the width of the peaks obtained in an electropherogram. This way of working results in resolution values that are more realistic as all possible variances are considered (not only longitudinal diffusion in Eq. 17.42). Assuming that the migrating zones have a Gaussian distribution, the resolution can be expressed as follows ... 

Polyamides containing thymine photodimer units in the main chains showed excellent resolution values (0.3 p m) and behaved as positive photoresists. It is concluded that polymers containing pyrimidine bases displayed high resolution and high sensitivity when used in both negative and positive photoresists formulations. 

On the other hand, optionally added co-ions of the eluent may also interfere with the ion-exchange process through competitive ion-pairing equilibria in the mobile phase. The effect of various amines added as co-ions to the polar-organic mobile phase was systematically studied by Xiong et al. [47]. While retention factors of 9-fluorenylmethoxycarbonyl (FMOC)-amino acids were indeed affected by the type of co-ion, enantioselectivities a and resolution values Rs remained nearly constant. For example, retention factors k for FMOC-Met decreased from 17.4 to 9.8 in the order... 

FIGURE 7 A schematic diagram showing two closely eluting peaks at various resolution values from 0.6 to 2.5. Figure reprinted with permission from Reference 7. 

Resolution values can be used to determine if further optimization of a chromatographic procedure is required, as they provide a numerical indication of whether two peaks have been completely resolved. Figure B4.2.3 compares two separation results one with completely resolved peaks and the other with incompletely... 

Representative resolution values are tabulated in Table 1.6. Resolution values are typically greater than 1.5 and are generally expressed as a range of values. 

The effect of selectivity, capacity factor, and efficiency on resolution is illustrated in Figure 1.9. Typically, an R value greater than 0.8 is required for accurate quantification of two peaks. A value of 1, for two equally sized peaks, indicates an overlap of about 2% for one band over the other.29 Chromatograms of two peaks of unequal sizes for given resolution values are shown in Figure 1.10.30... 

In figure 1.8 the theoretical peak capacities are given for some typical ranges of capacity factors as a function of the number of plates. The resolution values were taken to be equal to one. In the logarithmic plot of figure 1.8 a straight line is obtained with a slope of 1/2. A typical packed column with 5000 plates turns out to yield a peak capacity between 17 (case a) and about 50 (case c). An open column with 200,000 plates may accommodate 100 peaks with capacity factors between 0.2 and 2 (case a). 

Summation of resolution values has been used by Berridge (414] and summation of separation factors has been suggested by Jones and Wellington [408]. 

In the introductory section of this chapter it was shown that a straightforward summation of resolution values does not yield a satisfactory criterion for the evaluation of complete chromatograms (see figure 4.1 and table 4.1). A problem that can readily be appreciated from the example given there, is that the sum of Rs values will be determined mainly by the largest values of Rs that occur in the chromatogram. For example, in the... 

Figure 4.6 Variation of the sum of peak-valley ratios as a function of the number of plates for the two chromatograms (a and b) shown in figure 4.1, and for a third chromatogram (c), shown in figure 4.8. P was calculated from eqn.(4.10). Negative values for P were set equal to zero. The sum of resolution values is shown as a dashed line for chromatogram a only.

Drouen et al. [410] have recognized this problem and proposed a solution by using a product of normalized resolution values. They divide every value of Rs by the average Rs value (R J, where the average is taken over all the pairs of peaks in the chromatogram ... 

Maximization of the minimum resolution value observed in the chromatogram (eqn.4.25) corresponds to aiming at the minimum number of plates required to effectuate the separation. 

In the case, where the dimensions of the column are to be optimized after completion of the selectivity optimization process, another time factor may be even more appropriate. The first step to be taken after the completion of the optimization process is to establish the required number of plates (JVne). If the lowest resolution value encountered in the chromatogram is Rs min, and if the required resolution is Rs ne, then... 

Reducing the resolution values to be less than 1.5 for each pair of peaks by increasing segment slopes and shortening isothermal periods. 

The individual retention times of all solutes in a 14-component sample mixture were measured and used to calculate resolution values (eqn.1.14, because eqn.1.22 is invalid) between each pair of peaks in the chromatogram. The largest value for the limiting resolution (max Rsmin eqn.4.25) was used as the optimization criterion. 

Figure 1.9. Comparison of resolution values for peaks of equal and nonequal heights. Reproduced from the Journal of Chromatographic Science by permission of Preston Publications, Inc. 

FIGURE 1-4. Resolution of two chromatographic peaks at a resolution value of 1. 

FIGURE 1-5. Comparison of overlapped peaks at several resolution values. 

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