Dean Switch Problem

Hello, im having a problem with a 2d GC using the Deans Switch system.
Its a 8890 GC with 2 FIDs.
The problem is that, when cutting peaks from the 1st dimension to the 2nd dimension (2nd column), all peaks on the 2nd dimensions get split into 2 peaks.
Its not a inlet problem - if it was, all peaks would show up as 2 peaks also on the 1st column (Monitor FID).

Heres the chromatogram of a standard only separated using the 1st column and going to the Monitor FID:

The peaks look fine.

chromatogram before activating the valve

Here are both Chromatograms when the Dean Switch is in use, switching times are set, and 3 compounds are going to the 2nd column (and 2nd FID).

Thats where they show up split. A 2nd peak is adjacent to the main peak.

Any ideas?

  • Hi!

    It looks that your CFT system is not well configured. Those are not peaks. When your Dean system switches it creates some fluctuation in your flow, and it takes time to equilibrate.

    There is CFT Dean Switch calculator to optimize your restrictor flow.

  • thanks for the reply after 4 months, i still didnt find a solution for this problem. regarding the restrictor flows, i used the deans switch calculator software that came with a cd. your equilibration theory is invalid unfortunately, because - if i set the switching time 5sec earlier / or even if i set the solenoid valve to "on" during the entire run, which sends the whole chromatogram to the 2nd column, i always get a "double peak" on the 2nd dimension (FID2) for every single peak on the 1st dimension (FID1).

    also, the 2nd "peak" is definitely part of the compound and not caused by a fluctuation problem, since it also increases with the standard concentration :

  • Ok,

    Has this system had even work properly, when before this problem started, or this configuration just made? And you are trying to optimize it. Need more information.

  • no this never worked properly, i installed the DS/valve/columns ect myself and found that using the settings/pressures calculated in the dean switch calculator couldnt even send the compounds to the 2nd column when the switch was turned on -> then i played around with/increased the pressure of the epc until i accomplished sending compounds to column 2 when "on" and leaving them on column 1/restrictor capillary when "off" ... this double peak phenomenon is the best result i could get.

    is there a way to contact u directly? (telegram/wa)

    thanks for the help. DS seems to be a very niche application.

  • Ok, I got it.

    This does not work in this way. Because of too high pressure your peak could split into 2 and also you should take care about 0 dead volume.

    The DS calculator can pick you working pressure of second column and the restrictor length, The pressure program must be "Constant pressure", because you do not want to change in your splitting method. 

    You can contact me via WA my number: +77783279924

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