GC/MS Wont Run in Splitless Mode but Runs in Split Mode

Hi all,

We are running a 7890A/5975C GC/MS.  The instrument runs when in split mode, but when switched to splitless the sample will not inject.  We have always run splitless injections.  The instrument will be initially ready and becomes not ready just prior to sample injection during the prerun due to the pressure in the inlet suddenly increasing above the set value and staying elevated.  This leaves the syringe just sitting in the sample vial.  I have tried general maintenance on the inlet and replaced the septum, gold seal, inlet liner, as well as recutting and reinstalling the column to the GC. None of this seemed to be the issue. Not sure if anyone has any ideas on how to resolve this issue? 

Thanks!

  • What are the inlet and column configurations, flow rates, pressures, and timing setpoints?  The fastest way to share that is to copy/paste the contents of the file   acqmeth.txt    that lives underneath your specific   Our_Run_Method_Name.M   subdirectory in Windows Explorer.

    The 7890A Troubleshooting manual is available G3430-90017.pdf (agilent.com)

    Page 97...

    Please run the SS Split Vent Restriction Test, page 157, and the Inlet Trap Check, page 155.

  • Thanks for the comments I have pasted the requested information below:

    This is a new one for us as our lab has been running these instruments for 20+ years and can't ever  remember this as a problem. We run trace level organics and almost always  splitless, we tried the split method and was surprised to see it worked fine while the splitless still hangs up.  

    We have dual columns set up on the back inlet with one running to the MS and one running to an FID and are using a double tapered, splitless, inlet liner.   Here's one method:

    GC
    GC Summary
    Run Time                                     52.13 min
    Post Run Time                                0 min
    Oven
    Temperature
    Setpoint                                     On
    (Initial)                                    50 °C
    Hold Time                                    0.32 min
    Post Run                                     0 °C
    Program
    #1 Rate                                      20 °C/min
    #1 Value                                     120 °C
    #1 Hold Time                                 0 min
    #2 Rate                                      5 °C/min
    #2 Value                                     300 °C
    #2 Hold Time                                 12.31 min
    Equilibration Time                           0.5 min
    Max Temperature                              325 °C
    Maximum Temperature Override                 Disabled
    Slow Fan                                     Disabled
    Sample Overlap
    Mode                                         Sample overlap is not enabled
    ALS Errors                                   Pause for user interaction
    Front SS Inlet H2
    Excluded from Readiness                      ***Excluded from Affecting GC's Readiness State***
    Mode                                         Splitless
    Heater                                       Off
    Pressure                                     Off
    Total Flow                                   Off
    Septum Purge Flow                            Off
    Septum Purge Flow Mode                       Standard
    Purge Flow to Split Vent                     45 mL/min at 2 min
    Liner                                        A Liner has not been selected.
    Back SS Inlet H2
    Mode                                         Splitless
    Heater                                       On    250 °C
    Pressure                                     On    1.7232 psi
    Total Flow                                   On    48.6 mL/min
    Septum Purge Flow                            On    2 mL/min
    Septum Purge Flow Mode                       Standard
    Gas Saver                                    On    20 After 2 min mL/min
    Purge Flow to Split Vent                     45 mL/min at 2 min
    Liner                                        A Liner has not been selected.
    Thermal Aux 2 (MSD Transfer Line)
    Temperature
    Setpoint                                     On
    (Initial)                                    280 °C
    Column
    Column #1
    Flow
    Setpoint                                     On
    (Initial)                                    1.6 mL/min
    Post Run                                     2 mL/min
    Column Information                           J&W 123-5562
    DB-5ms cond 12-02-11; 2011-60m               
    Temperature Range                            -60 °C—325 °C (325 °C)
    Dimensions                                   60 m x 320 μm x 0.25 μm
    In                                           Back SS Inlet H2
    Out                                          MSD 
    (Initial)                                    50 °C
    Pressure                                     1.7232 psi
    Flow                                         1.6 mL/min
    Average Velocity                             48.4 cm/sec
    Holdup Time                                  2.0661 min
    Control Mode                                 Constant Flow
    Column #2
    Pressure
    Setpoint                                     On
    (Initial)                                    1.7232 psi
    Post Run                                     0 psi
    Column Information                           Agilent 123-5562
    2012-60m1                                    
    Temperature Range                            -60 °C—325 °C (325 °C)
    Dimensions                                   60 m x 320 μm x 0.25 μm
    In                                           Back SS Inlet H2
    Out                                          Front Detector FID
    (Initial)                                    50 °C
    Pressure                                     1.7232 psi
    Flow                                         0.31822 mL/min
    Average Velocity                             6.7659 cm/sec
    Holdup Time                                  14.78 min
    Control Mode                                 Constant Pressure
    Column Outlet Pressure                       0 psi

    I also went ahead and ran the inlet trap check with a flow rate of 400 mL/min and it resulted in a inlet pressure of 0.946 psi, which seems lower than what it should be based on the values provided in the manual for a clean split flow path.  We were again using a double tapered, splitless, inlet liner. Would this have an impact even though we are having issues in splitless mode?   I also went ahead and ran an inlet leak test and it is resulted in a total flow of 0 compared to the column at 3.61.  Is this pointing towards a flow restriction in a gas line? Thanks!

  • Recommendations:

    Increase the Oven Temperature equilibration time from 0.5 minutes to 1 to 1.5 minutes. The GC oven walls need more time to cool down from 300° C back to 50° C to be ready for the next run. This affects run-to-run reproducibility.

    The starting inlet pressure is only 1.7232 psi of hydrogen - which is less than the >5 psi minimum for decent flow/pressure control. This also means that column 2 flow is only 0.318 ml/min - in a 0.32 mmid column that is far below the optimal linear velocity for good chromatography. 

    This 1.7232 psi is for 1.6 ml/min of hydrogen carrier gas flow into the MS. The system's pumping speed for hydrogen is only 60% that for helium. The optimal flow into the ion source using hydrogen is 0.4 to 1.0 ml/min.

    The Gas saver is set to 20 ml/min after 2 minutes - AND the Purge flow to split vent is set to 45 ml/min at 2 minutes.  So the Spltless liner purge flow doesn't happen, the inlet just goes to Gas Saver mode at 20 ml/min.  2 minutes for Purge Flow to Split Vent is long with the column flows you have configured anyway. The liner volume is ~800µL and at your current flows, 1.6+0.32= 1.92, the liner is swept in ~ 25 seconds so the typical Purge Flow to Split Vent time for Splitless for that would be like 50 at 0.5 minutes.

    When did you switch to hydrogen carrier gas?  Do you use tanks or a hydrogen generator?

    The inlet test results in the manual were written with helium in use. 400 ml/min of hydrogen is easier to push than 400 ml/min of helium so the lower pressure in the trap test is typical.  During the inlet leak test if total flow went to zero there was no flow in the inlet.   What is your hydrogen supply pressure?  Are there traps on the line?  If you use a hydrogen generator is there moisture in the supply lines - that can damage the electronic pressure control modules.

    What parts are being used to install two columns to the inlet?  Remove both columns, reinstall only the one to the MS, configure and save a method with those parameters, and check again.

    This column configuration is an issue using hydrogen carrier gas.  I would recommend that with hydrogen carrier gas you change to 2 x  20m×180µm columns with column 1 at 0.9 ml/min, 7.7939 psi inlet, and column 2 would be 0.5157 ml/min, good for a 180µm column.

  • Increasing the inlet pressure to >5psi seemed to have fixed the issue!

    I appreciate all of the recommendations.  We just recently switched over to hydrogen carrier gas in the last few months so still working of transitioning methods over.  Used the agilent method converter for helium to hydrogen and we are using a hydrogen tank.  Obviously are a few things that still need to be adjusted within the methods.  Worked well for the last few months even with the low pressure and all of a sudden decided to have issues.  I will certainly take into consideration all of these recommendations for the method and column configuration moving forward.  

    I very much appreciate all your help and expertise in resolving this issue for us.  

  • 5 psi inlet pressure running hydrogen with your configuration leads to 2.3 ml/min to the MS and 1.02 ml/min to the FID.

    You are welcome. Are you using a two-hole ferrule in the injection port or a splitter of some type? The two-holed ferrules are...touchy.  They work right up until they don't and you can't always tell when that happens.

    user-guide-coverting-ei-gcms-instruments-5994-2312en-agilent.pdf

    Please buy the 9mm extractor or Draw out plate for the ion source, too. The details are in the conversion document above.

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