Pump and Flow Control
Pump Commands

The following commands are supported for pump and/or flow control:

Hold/Continue Gradient

Alternatively, the following short command is valid:

Stop Pump Flow/Gradient

Determining Pressure Limits (see Pressure.Lower/UpperLimit)

 Note:

The pressure unit (bar, MPa, or psi) depends on the pump type.

Generating a Flow or % Gradient

The flow or solvent value determined for the time t is continually adjusted to the following flow or solvent command. If the two values coincide, the flow or solvent value is kept at a specific level (see ramp profile 0 to 1), if they differ from each other, the value is modified. The difference between the two time values corresponds to the length of the ramp (see ramp profile 1 to 2min).

 Tip:

Dionex GP40/GP50, IP20/IP25, IC20/IC25/IC25A, GS50, and IS25 pumps do not deliver flow gradient ramps. Instead, changing the flow rate between one time value and the next results in an immediate change in the flow rate (step change).

To determine a sharp increase, two different values must be defined at the same time. The start and end values must be entered at the exact times (see rectangle profile at the time t=1min).

By combining the just mentioned possibilities, any multi-step gradient profile can be realized. For example:

Instead of the arbitrarily selected quantity %B used in these examples, any other solvent (see %B, %C, %D) or the flow rate can be changed.

Creating a Non-Linear Gradient Ramp (Dionex GP40/GP50/GS50 pumps only)

A Curve command (also, refer to Gradient Curves) instructs the pump to apply the selected curve number when adjusting the solvent composition between two retention times. In the example below, the Curve = 8 command at 2 min creates a concave ramp between 1 and 2 min.

Consecutive commands with identical solvent compositions generate an isocratic segment, regardless of the curve number selected (see 0 to 1 min and 2 to 3 min below).