Pump and Flow Control
Determining a Gradient

There are two ways how to determine a Gradient. You can do this either manually on a control panel or automatically via a program:

On a control panel

Different dialog boxes are provided for each device for which a gradient can be determined. Use these dialog boxes to enter the device-specific settings. A gradient can be run either as a ramp or as a Step Gradients (in IC, also as a Gradient Curve).

  1. Open a control panel for the device for which you want to define a gradient.

  2. Select Flow on the Control menu
    - or -
    Press <CTRL> + <F>.

  3. Determine the desired gradient on the Gradient tab page (see below).

In a program

The easiest way to create a new program is to use the  Program Wizard.

  1. On the File menu, click New, and then select Program File.

  2. On the Pump Options page, select Multi-Step Gradient. The Flow Gradient Options dialog box appears. This dialog box corresponds to the Gradient page during manual input.

Entering "Basic points"

  1. In the Retention column, enter the time (relative to the injection time) of the desired modification.

  2. In the Flow column, enter the new value for the flow rate.

  3. In the %B, %C, and/or %D columns, enter the new value for the delivered solvent composition. %A is the difference between the total of the entered values and 100%.

  4. For Dionex GP40, GP50, and GS50 pumps only: Enter a value in the Curve column to determine whether the pump delivers a linear or Curved Gradient. Curve 5 (the default) is linear; curves 1 - 4 are convex upward and curves 6 - 9 are concave upward.

  5. Click Insert Line to append another line to the table. After appending the first new line, further lines are appended automatically, as necessary. Enable or disable this option by selecting or deselecting Autom. Append New Lines on the context menu.

    Tips:

    Click Delete Line to remove unnecessary lines from the table.

    If an entry is invalid, the input in the corresponding cell is displayed in red color. Invalid entries must be corrected immediately.

    Click Clean Up to delete superfluous information from a previously selected area.

    To calculate missing values between two or more time values can, click Interpolate. The values are automatically added to the table.

    Select Fill Column on the context menu to fill the cells in the column with the currently selected value. Only the cells below the selected value are filled.

In a graphical representation, each flow and solvent value of the value table is represented as a point. By interpolation between the basic points of a column, an area gradient profile is created. The solvent areas are represented in the color of the corresponding caption; the flow rate is displayed as a thin line.

Direct Input into a Program

If you know the Program syntax, you can directly determine the gradient in the program. Entering the %B, %C, %D and Flow commands in the program allows you to change the solvent composition and flow rate at a precise time. The gradient profile results from the change in value of a certain quantity at the time t.

 

 Tip:

The 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).

Example:  The three different profiles are realized via the commands listed below the profiles.

 

Rectangle Profile

Ramp Profile

Multi-Step Profile

0.000 %B.Value = 20

0.000 %B.Value = 20

0.000 %B.Value = 20

1.000 %B.Value = 20

1.000 %B.Value = 20

0.500 %B.Value = 20

1.000 %B.Value = 40

2.000 %B.Value = 50

1.500 %B.Value = 40

2.000 %B.Value = 40

 

2.000 %B.Value = 40

2.000 %B.Value = 20

 

2.000 %B.Value = 30

 

 

2.500 %B.Value = 30

 

 

2.500 %B.Value = 20

 

For a rectangle profile, indicate exactly how long the specific solvent composition is valid. If the composition is changed at the same time as another percent command is defined, the change in solvent composition is executed immediately. The solvent percentage achieved is then maintained until replaced by another command.

To realize an increase over a longer period, the start value and end value must be specified with the precise time. The difference between the two time values corresponds to the duration of the increase (see ramp profile).

You can realize any multi-step gradient profile by combining the above-mentioned possibilities.

For more information about how to determine a gradient in GC, refer to  Determining a Gradient (GC).