Half-width. chromatographic

Peak asymmetry or skewing is a well-documented (4,6,7) characteristic of chromatographic peaks and is measured easily by ratioing the peak half widths at 10% height as shown ... 

Peak Area by Multiplication of Peak Height and Half Width Often, a chromatographic signal may be approximated by a triangle. The calculation of the area is performed as shown in Figure 9.2 ... 

The fundamental principles of operation of an immobilized enzyme flow analyser have been studied. Models were developed to explain the dependence of peak area, height, and half-width on sample concentration, sample volume, system flow rate, and column size. The dependencies were analogous to the behaviour of a concentration-sensitive chromatographic detector. 

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. 

For high-throughput analysis, it is important to increase the specihcity of each bioanalytical method. The enhancement of chromatographic resolution presents various limitations. Better selectivity can be obtained with TOF mass analyzers that routinely provide more than 5000 resolution (full width at half-mass or FWHM). The enhanced selectivity of a TOF MS is very attractive for problems such as matrix suppression and metabolite interference. In one report of quantitative analysis using SRM, TOF appeared less sensitive than triple quadrupole methods but exhibited comparable dynamic range with acceptable precision and accuracy.102... 

The broader a chromatographic peak is relative to its retention time the less efficient the column it is eluting from. Figure 10.2 shows a chromatographic peak emerging at time t, after injection the efficiency of the column is most readily assessed from the width of the peak at half its height and its retention time using Equation 1 ... 

One recommendation for LC detectors3 is that the time constant should be less than 10% of the peak width at half height, wh. Thus, a peak width of 50 xL at a flow rate of 1 mL/min corresponds to a time constant of 0.3 sec. This is the order of magnitude needed for most chromatographic detectors. 

Interpretation of Chromatograms Fig. 1 represents a typical chromatographic separation of two substances, 1 and 2, in which fR(i) and fR(2) are the respective retention times h, hJ2, and are the height, the half-height, and the width at half-height, respectively, for peak 1 and Wi and W2 are the respective widths of peaks 1 and 2 at the baseline. Air peaks are a feature of gas chromatograms and correspond to the solvent front in liquid chromatography. 

Care must be taken in the use and interpretation of literature efficiency values. Efficiency values are likely the most incorrectly calculated chromatographic figure of merit. The commonly used equations based on peak width at the base or at half the height of the peak are valid only for perfectly Gaussian shaped peaks. This problem has been realized by chromatographers for some time, but the popularity of these methods continues because until recently the only alternative was computer based moment calculations. Kirkland et al. addressed this problem and recommended that peak symmetry values be reported along with efficiency values (8 ). They further showed that the calculation... 

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