Instrument Type:
Pump
Related Commands:
Description:
The solvent and thus the flow usually consist of different individual components. The respective amounts of the partial flow are indicated in percent of the flow. The total sum of all partial flows (solvent components) is 100% (%A+%B+%C+%D=100%), where %A is calculated from the remaining partial flows (%A=100%-(%B+%C+%D)). It is therefore sufficient to determine the values for %B, %C, and %D.
Changing the solvent composition during the analysis is referred to as gradient (or more exactly as %-Gradient).
%A, %B, %C, and %D define the partial flow rates of the individual pumps in a high pressure mixing system (as %-values of flow), or the partial flow rates on the suction side of a low pressure mixing system. The latter generally refers to a single pump or a separate mixing vessel with controlled proportioning valves. The formation of %-gradients is by the same principle as for Flow.
For each Timebase, one or more fluidic systems can be installed. They can be controlled independently, either manually or via a Program.
In case a second fluidic system is installed, the corresponding device name has to be specified in the program. Use the F8 key or the Program Wizard to insert the device name automatically.
Tip:
The Hold, Continue, and StopFlow commands are always effective for all fluidic systems.
Function:
With Ramps, the partial flow rates of A, B, C, and D change linearly with time between two %A, %B, %C, or %D commands. By entering two percent commands at the same time, you can program Step Gradients. When sorting, the editor does not change the order of commands having the same program time! If the partial flow rates are to remain constant during analysis, that is, isocratic, the appropriate %A, %B, %C, and/or %D commands need only be entered at the beginning of the file.
-2.000 Flow = 1.000
%B = 20.0
... ...
0.000 Inject
0.500 %B = 20.0
%B = 40.0
... ...
8.500 %B.Value = 80.0
8.500 End
In this example, the total flow rate remains constant at 1.0 ml/min. %B also remains constant, at 20% from -2.0 to 0.5 min, then increasing abruptly to 40%, then linearly to 80% with a gradient of 5%/min.
Parameters:
Value
Partial flow of the solvent component [%]
Equate
Name of the solvent component
Type
(P580 only)
Solvent type of the respective component
Tip:
Dionex recommends the following setting:
Isocratic and LPG pumps: Automatic
HPG pumps: Custom
With HPG pumps, set the pre-compression control via the Learn and Freeze commands.
Tips:
Chromeleon is able to run flow and %-gradients simultaneously. However, in high pressure mixing systems, this results in non-linear partial flow rate changes for each individual pump.
Note that due to compressibility and dead volume considerations, high pressure and low-pressure applications are not always interchangeable!
The %-values remain constant from the last %-command to the end of the program. Thus, for isocratic operation, a single %-entry at the beginning of the file is sufficient.