Setting the Bypass Mode OptionsCreating and Modifying Programs
Setting the Bypass Mode Options
The Dionex autosamplers with split-loop injection feature a bypass mode that reduces the gradient delay time and minimizes the flush time. The Program Wizard (see The Control Program 
The Program Wizard) supports the bypass mode for the Summit x2 Dual-Gradient HPLC System and the UltiMate 3000 HPLC system.
When the Bypass Mode is enabled, the chromatographic flow bypasses the sample loop of the autosampler. For this purpose, the injection valve is switched into the Load position with the related autosampler command. The solvent flows directly onto the separator column.
Tip:
Make sure that the system runs under isocratic conditions until switching to the bypass mode.
To avoid carry-over, bypass the sample loop only after the entire sample has left the sample loop. To ensure this, purge the loop volume and the void volume between the injection needle and the injection valve at least five times.
The bypass time, i.e., the time after which the injection valve is switched, is calculated as follows:
Time = FlushFactor * (Max. Inj. Vol. + void vol. between injection needle and injection valve) / Flow
The void volume between the injection needle and the injection valve is 20 µl. Set all other parameters in the Program Wizard. On the Wizard Options page, select Program for x2 Tandem Operation, and create the program on the next wizard pages. To enable the Bypass Mode, select the related check box on the Tandem Operation Options page:
Select the following settings:
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Max Inj. Vol. |
Enter the maximum injection volume for the application. |
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Flush Factor/Flush Out Factor (WPS-3000SL/RS/TXRS) |
Enter a factor for calculating the purge volume.
Dionex recommends using a factor of = 3. The appropriate factor, however, should be verified for each application individually. |
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Time |
Usually, the time is calculated from the above settings: Time = FlushOutFactor * (Max. Inj. Vol. + void volume between needle and injection valve) / Flow Enter a time if you want to limit the time until bypass mode is enabled. In this case, the flow is recalculated as follows: Flow = FlushFactor * (Max Inj. Vol. + void vol. between injection needle and injection valve) / Time. |
At the bypass time, the MsvToLoad (ASI-100) or InjectValveToLoad (WPS-3000SL/RS/TXRS) command is added to the program file. The chromatographic flow bypasses the sample loop of the autosampler.
Tip:
In addition, enter the PrepareNextSample command about 1 minute before injection of the next sample to load this sample into the loop and inject it immediately after column valve switching.
For program examples, refer to:
Creating a Tandem Program (including Bypass Mode) for an UltiMate 3000 HPLC System
Creating a Tandem Program (including Bypass Mode) for a Summit HPLC System