sodium acetate in sequencing gel buffers!

[zarir]

Hi people,
i want to know the reason for adding sodium acetate to the lower buffer
tank while doing manual sequencing. I know it reduces compressions, by
altering the voltage gradient, but how? what is the chemistry involved?
Please reply urgently.also some reference where it is documented.
thanks,
zarir E.V.
dept. of agronomy,
purdue university.
zarir at dept.agry.purdue.edu