Foley Dorsey equation

Asymmetric peak and Foley-Dorsey equation terms. 

The kinetics of the chromatographic process is linked to efficiency. The number of theoretical plates, N, that measures column efficiencies, is best estimated using the Foley-Dorsey equation when a departure from the Gaussian symmetrical peak shape is noted [9] ... 

J. P. Foley and J. G. Dorsey, Equations for Calculation of Chromatographic Figures of Merit for Ideal and Skewed Peaks, Anal. Chem. 1983,55, 730 ... 

Foley and Dorsey have recently derived a simple manual method for the calculation of plate counts that corrects for the asymmetry of skewed peaks (9 ). This equation has been used in all of our micellar efficiency calculations and is ... 

The efficiency remains high even with high concentrations of methanol. With acetonitrile as the modifier, the efficiency was significantly reduced as the concentration of the modifier was increased. For this study the theoretical plate number (N) was estimated using the equation of Foley and Dorsey (5M. 

Foley and Dorsey (1983) have considered the effect of peak tailing on column efficiency and concluded that measuring peak widths at half height (equation (2.26)) substantially overestimates the number of theoretical plates of a tailed peak. Thus resolution (equations (2.46) and (2.47))... 

Foley, J.P. and Dorsey, J.G. (1983) Equations for calculation of chromatographic figures of merit for ideal and skewed peaks. Anal. Chem. 55, 730-737. 

One most frequently used equation is called the Exponential-Modified-Gauss (EMG) function (Jeansonne and Foley, 1991 and 1992 Foley and Dorsey 1983 and 1984). It is defined as a Gaussian peak (Eq. 6.143) superimposed by an exponential decay function hexp... 

The assumption for the measurement of peak widths in Eqs. (8)—(10) is that the peak is Gaussian. Unfortunately, few peaks are truly Gaussian and, in general, for asymmetrical peaks, N, calculated by a Gaussian-based equation, increases the higher up on the peak the width is measured. Figure 3 shows the error in plate-count determinations for asymmetrical peaks as a function of the peak height at which the width is measured. A more accurate approach to efficiency measurement has been presented by Foley and Dorsey (7), which takes into account the peak asymmetry. 

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