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Switch to splitless and now never ending problems, but only on one inlet?

eme091

I am using a GC6890N S/N US10124020 Firmware N.06.07 With auto injector and tray: G4513A, SN:CN1540278, FW:A.10.09 and G4514A, CN15450061, A.10.16.  We were running on the back detector Splitless, pressure:5.4, Total flow:350.7ml/min, Column Const Pressure, Flow:6.8ml/min DET is FID.   Not sure what else would be relevant but I guess on to the QUESTION

     On one occurrence the back inlet would not maintain the pressure it always sat 0.1 below the setting.  After checking all the normal things, column install, inlet, liner all fittings I moved the column to the front and it ran fine.  No other methods run on the back have an issue.  Recently another coworker went to run this method on the back again.  No pressure issues.  After running the method 3 times the system suitability failed area ratio of the peaks all times and areas were sometimes erratic.  Making me think it is an injection problem, but as it is a ratio %RSD the ratio of the same vial being injected should not be really effected if the needle has a small air bubble problem effecting the injection volume.  The analyst moved to the front inlet same injector, and solution . . . no problems.

 

The issue method is also the only splitless method we run on the back inlet all other are split and they run fine.  Is there something that could get clogged that could affect a splitless method and not a split?  Could this be something else.

 

 

 

Any help or suggestion would be greatly appreciated.

 

THANKS!

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  • 0

    Are you using a packed or megabore column? I have only used capillary columns where 1 ml/min is normal, so 6.8 ml/min column flow is high. You might also consider replacing the split vent trap (part #: 5188-6495). It rarely causes problems, but when it does get clogged up, it causes squirrely flow problems.

  • 0 in reply to stevenwlloyd

    It is a capillary, USP 401

                   The gas chromatograph is equipped with a flame-ionization detector, maintained at a temperature of about 260°, a splitless injection system,                and a 0.53-mm × 30-m fused-silica capillary column bonded with a 1.0-µm layer of phase G16. The chromatograph is programmed to                maintain the column temperature at 70° for about 2 min after injection, then to increase the temperature at the rate of 5°/min to 240°, and                finally to maintain this temperature for 5 min. The injection port temperature is maintained at about 220°. The carrier gas is helium with a                linear velocity of about 50 cm/s.

    When I set the average velocity to 50 cm/s forces the pressure to 5.4 psi, flow 6.8 ml/min, total flow of 356.5ml/min.  So yea I thought it was a little weird.

     

    Thanks

  • 0 in reply to eme091

    What is your flow through the split vent trap/gas saver flow? You must be consuming gas a phenominal rate. This would explain why your total flow volume is high.

    Another thing is that have you configured the correct column in the software for the back inlet? If this is out then the software calculations of flow rate, inlet pressure, general chromatography will be irratic and uncontrolled.

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