What Is a Linear Salt Gradient?

[Herodotus]

Can anyone tell me what a linear salt gradient is?

 

[Borek]

It means that concentration of salt changes linearly, either with time or with space. Most likely you are looking for the first case (linear change of concentration in eluent)

c = c_0 + kt

k - some constant
t - time
c₀ - initial concentration.