Dilutions for Standards are calculated using the formula C 1 . The gradient starts off with pure water until the sample is loaded onto the front of the column. This runs until the end when we go back to pure water to get ready for the next run. You can see the baseline rise and then fall from roughly 0.5 to 2.5 m S as we go through this gradient. The ultimate purpose of a gradient is to spread out the analytes which are weakly retained and tend to bunch together, and to compress or more rapidly elute those which are strongly retained by bringing in the strong eluent.
Gradients always go from a weak eluent to a strong eluent.