# Plate Theory and Extensions - The Gaussian Form of the Elution Equation > Page 43

Thus, expanding (X_{m(n)})
as a series ,

As (n) is
large and the whole elution curve for any solute is virtually contained between
w = - and w = (*i.e*.,
contained within four standard deviations of the Gaussian curve).

Thus, will always be very much greater than and so, and all higher terms can be ignored.

Therefore