A Brief Introduction to Snyders Theory of Gradient Elution

Appendix 3.3 A Brief Introduction to Snyder s Theory of Gradient Elution 

Consider the analyte band part way along the column (fractional distance x) as it is eluted by a solvent gradient. At any such point a differential flow dV of mobile phase will cause a corresponding movement dx of the analyte band, given by (Snyder 1964)  

Now a crucial approximation is made, namely, k j = k a. This implies that, at any given instant during the gradient, the composition of the mobile phase currently present within the column does not vary much as a function of X. Under this approximation we substitute k in Equation [3.57] by k j from Equation [3.17]  

Equation [3.19] gives the retention volume for the analyte under gradient conditions specified by the parameter h. It is now simple to derive a value for the corresponding elution time g = Vg/U  

The value of k[, the value of k at the moment of elution from the column, is obtained by substituting V in Equation [3.17] by (Vg —V ) from Equation [3.19], with some simple algebraic rearrangement to give  

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