Peak, asymmetry definition

FIG. 16-32 Exponentially modified Gaussian peak with Xq/Gq = 1.5. The graph also shows the definition of the peak asymmetry factor at 10 percent of peak height. 

Because of its pragmatic definition P automatically reflects peak asymmetry and it can be applied to peaks of all shapes, not exclusively to Gaussian peaks. 

Although theory predicts that chromatographic peaks will be symmetrical, peak asymmetry is common, even in the most carefully controlled analytical and preparative separations. The most rigorous definition of peak asymmetry is given by the peak skew (y), which is related to the second (M2) and third moments (M3) of the Gaussian distribution ... 

Should one wish, these variables can easily be converted back to their expanded form through the definitions given in Equations 7 -9. Our measure of peak asymmetry is the ratio of half widths,... 

Figure 1.12. The 10% peak height definition of the asymmetry factor. The asymmetry factor is equal to the ratio A / B.

Peak asymmetry can also be measured using the U.S. Pharmacopoeia (USP) definition, which defines the first section of the peak as/and the peak width as the value at 5% of the peak height (see Figure 2.17) ... 

Absorption, 6, 8, 40 Accuracy, definition of, 99 Activity coefficient, 109-110 Adjusted retention volume, 10 Adsorption, 6, 8, 40 Affinity chromatography, 224-225 Area, measurement of, 102 Area normalization, 104 Asymmetry of peaks, 14, 43... 

The observed asymmetry of a peak is measured by two parameters, the skewing factor a measured at 10 per cent of its height and the tailing factor TF measured at 5 per cent (for the definition of these terms, see Figure 1.4) ... 

Time averaging is symmetrical in time, which means that it will not induce asymmetry into an otherwise symmetrical input signal. Also, the peak height is not necessarily altered. The same is valid for pointwise time averaging, that is, the determination of the arithmetic mean of accumulated data during a given time interval at constant A. After this step the scan continues with a definite increment AA, accumulation starts at A + AA, etc. Both methods are applicable if the samples are stable and not damaged by radiation. 

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