Does anyone have problems with the 502 precursor being too high?

I ran an autotune and the tune evaluation. It says 502 precursor is too high and contact Agilent service engineer. Any thoughts on what could cause this?

  • The tune report says your column flow is 6.607 ml/min, which dramatically exceeds the maximum allowable flow into the GCMS.  Yours has a diffusion high vacuum pump and the absolute maximum is 2.0 ml/min or else damage could occur from backstreamed diffusion pump fluid.   Turn the flow down into the recommended 0.8 to 1.4 ml/min range, 1.2 ml/min is used on most systems, then tune again and post those results please.

    Tune ion peak precursors, splitting, and tilting/asymmetry are related to the quadrupole itself, but poor vacuum could certainly cause this.

  • I should have mentioned that this is a GC-MS/FID. 

  • What is the flow into the MS?  What is the configuration of the inlet, column(s), splitter, restrictors, etc?

    How many injections have been done on this 24 year old system?

    The most probably cause of tune ion peak precursors/splitting/tilting/asymmetry is that the quadrupole has sample residue deposited on it that is affecting the electrostatic Rf/DC fields that filter the ions.  The system needs remedial cleaning including the quad, quad radiator, source, source radiator, side plate, and the entire inside of the vacuum chamber to reduce the amount of sample residue that is continuously redistributing inside. A quad cleaning may resolve the precursor but without cleaning everything it will happen again sooner.

  • So this instrument runs air samples. It has probably done thousands. and thousands of injections.

  • How long is the piece of 0.25mm id capillary column going into the MS and what is the pressure at the end of the 0.53mm column? Or, what is the inlet pressure and the lengths of every segment with a diagram so that I can try to figure it out.

    Every time I walk up to any Agilent GC, I show the operator how to see the number of injections.   

    8890 and Intuvo:       Service Mode, Instrument, Usage

    7890:                           Service Mode, Diagnostics, Instrument Status

    6890:                           Options, Diagnostics, Instrument Status

    It might be worth venting and either put a 30x250x.25 column from inlet to MS, configure it properly, set it to 1.2 ml/min, let it pump for a few hours, and then try it again.  Or, vent and cap off the MS transferline. That is not necessarily a completely valid test, but will help see if too much flow is the issue or a contributing issue.

  • Inlet pressure is set at 12.0 PSI. The total number of injections 1000542.

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