Peak-valley ratio measurement

Figure 2. Measurement of the peak valley ratio used in several chromatographic response functions (equations 6 and 7).

Three definitions of peak-valley ratios are illustrated in figure 4.2. All of them express the extent of separation as some measure of the depth of the valley between two peaks divided by some measure of the peak height. The first criterion (P) measures the depth of the valley relative to the interpolated peak height as shown in figure 4.2.a. The corresponding expression is ... 

The second peak-valley ratio was suggested by Schupp [403] and is illustrated in figure 4.2.b. In this criterion, which we will refer to as the median peak-valley ratio (PJ, thedepth of the valley at a point midway between two successive peaks (fm) is measured relative to the average peak height (gj which equals the interpolated peak height at that point. The corresponding equation is ... 

Figure 5.4 shows the NDR peak measured in a nanopore test bed device containing a SAM of 1 at 60 K. Note that at about 1.75 V the SAM becomes conductive to a peak of 1.08 nA at about 2.1 V. The conductance then sharply drops to about 1 pA at 2.2 V. The SAM therefore acted as an electrical switch, turning ON then OFF depending on the applied voltage. The peak-to-valley ratio (PVR) was about 1000 1. 

If the valley did not touch the baseline, it would have a length (A-C) that would be less than the distance to the baseline. If we divide the length of A-C by the length of A-B, we have a mathematical measure of the baseline resolution for the two peaks. Summing these ratios of baseline resolution for every peak pair gives us a resolution sum for the whole chromatogram. 

The role of the mass analyser is to separate ions emerging from the ion source according to their mass (w/z ratio). The separating capability or mass resolution, R, of the analyser is measured in terms of its ability to resolve ions to less than a 10% valley between peaks ... 

Fignre 16.1 Explanation of the discrimination factor dg. Measured is the ratio of the distance between the apex of the smaller peak and the valley to the height of the smaller peak... 

Initially developed at Columbia University, flash chromatography is an air pressure driven hybrid of medium pressure and short column chromatography which has been optimized for particularly rapid separations. The resolution is measured in terms of the ratio of retention time (r) to peak width (w, w/2). It is measured by baseline resolution in the valley between the peaks and the distance from peak to peak. Sample size can be increased dramatically if less resolution is required. This innovative work by the Columbia University team demonstrated that column performance was quite sensitive to the rate of elution, and the best performance was accomplished with relatively high eluent flow rates. 

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