Peaks minimum separation ratio

On running the program,the Performance Criteria are first printed out and then the separation ratio of the critical pair is asked for on the monitor screen. After typing in the appropriate value, the capacity ratio of the first peak of the critical pair followed by the capacity ratio last eluted peak peak are then requested. The request procedure continues until all the necessary information has been entered after which the program runs. Some care must be taken when entering the minimum pressure, maximum pressure and pressure increment. If the range is made too large and the increment too... 

In order to optimize a separation and produce it in the minimum time, the capacity ratios and separation ratios must be measured for a given pair of enantiomers under known conditions of mobile phase composition and temperature (this will be discussed in detail later in this chapter). Unfortunately, when two peaks are eluted close together, which frequently occurs in chiral chromatography, the positions of the peak maxima are distorted due to the immediate presence of the other peak. An example of this problem is shown in figure 10.1, where the peaks are simulated and added, and the composite envelope plotted over the envelope of each individual peak. It is seen that the actual retention difference, if taken from the maxima of the envelope, will give a value of less than 60% of the true retention difference. Unfortunately, this type of error will probably not be taken into account by most data processing software. It follows, that if such data is used in an attempt to calculate the... 

Table 15.2 does not include any of the other useful qualitative information that can be gleaned from the Sanderson test spectrum analyses, such as the minimum separation and minimum peak ratios for reliable measurement. 

The minimum value of (specific column can be assumed to be equal to the ratio of the retention distance of the first peak plus its width at the base, to its normal retention distance. This assumption premises that resolution is satisfactory when the peak maxima are separated by 4a. 

Since the success of separation generally hinges on the isolation of singlets (which by definition are component peaks separated by minimum resolution R] on both sides), the success ratio is simply s over the number of components m... 

The separated components emerging from a GC column are present in pico-gram amounts in the carrier gas stream. If the column eluant is to be coupled to a mass spectrometer then the volume flow-rate of carrier gas should be minimised for a given separation to achieve high sensitivities in the ion source and reduce pumping requirements. GC parameters are selected to obtain symmetrical sharp peaks which are eluted in the minimum carrier gas volume and with the best peak height to width ratio that can be achieved. Clearly, the components need to be resolved, as co-eluting peaks would not produce pure mass spectra which could then be compared to a library of reference spectra. A number of factors need to be considered to optimise the GC system ... 

When the critical pair is separated, so are all other peaks in the chromatogram. If the critical pair is not the last two peaks in the chromatogram the separation time will be tR(l + nk) where n is the ratio of the retention factor of the last peak to elute in the chromatogram to the retention factor of the second peak of the critical pair. The fastest separation is obtained when tR is minimized. This will be the case if the following criteria are met. The minimum useful value for the resolution of the critical pair is accepted. The separation system is optimized to maximize the separation factor (a) for the critical pair. The retention factor for the critical pair is minimized (k 1 -5). The column is operated at the minimum value of the plate height, Hmin, corresponding to Uopt. 

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