Instrument Type:
Pump
Related Commands:
Description:
The Flow command defines the total flow rate (in [ml/min]) through the column, i.e., the sum of all Partial Flows (%A+%B+%C+%D=100%). The value entered represents the current value. For isocratic systems, this value remains constant during the program. In flow-gradient systems, this value represents an interpolation point of a polygonal line to which the previous and following flow values are adjoined by straight lines.
Function:
With flow Ramps, the total flow rate alters linearly with time, between two flow commands. By entering two flow 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 flow is to remain constant for the entire analysis, a single entry at the beginning of the Program is sufficient.
-2.000 Flow= 0.500
... ...
0.000 Inject
0.500 Flow= 0.500
0.500 Flow= 1.000
... ...
8.500 Flow= 5.000
8.500 End
In this example, the flow rate remains constant at 0.5 ml/min between -2.0 and 0.5 min. Then it increases abruptly to 1.0 ml/min and then linearly to 5 ml/min with a gradient of 0.5 ml/min.
If a second fluidic system is installed in the same Timebase, the corresponding device name has to be specified in the program. By using the F8 key for generating command lines, the device name is inserted automatically.
Tip:
The Hold, Continue, and StopFlow commands are always effective for both fluidic systems!
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.
As there are pressures up to 400 bars in the chromatography column and as solvent mixtures such as methanol/water are subject to volume compression, the volume delivered in High-Pressure Gradient Systems does not correspond to the volume transported via the column. However, the number of delivered and transported solvent particles is not changed by this fact.
The flow rate remains constant from the last flow command to the end of the program. Thus, for isocratic operation, a single flow entry at the beginning of the file is sufficient.
The first flow command must be at the beginning of the PGM File!
Normal flow rates are in the range 0.5 to 10 ml/min. Flow rates deviating from this range are achieved by using special micro pumps (0.1 - 0.5 ml/min) or preparative pumps (as from 10 ml/min).
Stopping the flow or decreasing the flow to 0.00 ml may result in deposits in the detector flow cell. To avoid this, turn off the lamp in UV and fluorescence detectors when the flow is stopped (Lamp = Off).
For Dionex detectors, a warning appears if the lamp is not turned off. However, make sure that you have selected the installed pump from Link to Pump list on the General tab page for the detector in the Server Configuration program.