Replace EM horn?

Hello all,
I recently cleaned my ion source (5977A - Extractor source) and installed two brand new filaments. On my tune report, the EM volts for both filaments are between 1950 and 2005; the gain factor is only 0.389; water and nitrogen are below 4%. Does this seem to indicate that I should replace my EM horn, or is it more likely that there is contamination of some kind? Or something else? The EM volts seem awfully high for two brand new filaments.
Thank you!
  • Hi

    First, you should clean ion source then check value of EM Horn..

    Generally, user change it after 2000( based on uses n application) but some user keep it use upto 3000 value of EM Horn..

    Generally, limit is 3000 but all depends on application and uses...

  • What was the EM Voltage before the source cleaning and filament replacement?  How old is the electron multiplier?   They do not typically fail, the tune EMV setting slowly gets higher and higher.  They typically work fine up to ~2500V or so and then the gain curve calculation starts having trouble as there's not enough higher values to use for the calculation.   Could you share a tune report from before and one from after the cleaning?

    Did you clean the source following the instructions in these videos?   Eliminate the Fear of Mass Spec    There is tons of good information there.

  • Attached are tune reports from before and after cleaning and changing the filaments (I was trying to correct chromatographic issues that seem mostly due to a contaminated precolumn and a small leak at the interface between the precolumn and the GC column). 

    I used the cleaning guide "Agilent GCMS Ion Source Cleaning Guide - May 7, 2015" from the Files section on the GC/MS page on this site.

  • Repeller value looks strange in tune report..Even in last report it's zero..

    After cleaning, all wires connected properly?

    Be sure, that atune file is not corrupted..

  • It's an extractor source etune....repeller zero is not unusual.

  • The cleaning and new filaments worked. The repeller voltage is now lower, extractor is lower, and Gain factor is lower.  The EMV before at 1900 means that the EM is not new and 1947.1 after means that it needed a couple more steps in voltage to get the 69 response in the required window.  Tuning is a dance with many partners - every parameter gets optimized and the path to that optimization is not always the same.  It needs a bit more EM now but that doesn't mean all that much as there are so many other small voltage changes. 

    Tuning is not like the tip of a needle - one very tiny point of perfection.  As long as the system tunes, the air/water is good, and your lowest injected standard peak heights are 3x to 4x the background noise, it's fine.  There's no reason to have peaks larger than a few million counts.  This system's air/water is fine. It needs a new high vacuum gauge.   I question running the transferline at 320 and the source at 230.  Is your final oven temp near 320?  The column is nearly at vacuum there so boiling points of all compounds is dramatically lower. 

    You're going to need to replace the EM someday. That's about all we know for sure.  They typically don't just die.   In the tune menus, File, View Tunes...

    Then look at the EM plot over time.  Is it going up slowly or was it going up slowly before and now going up quicker?  They tend to go up slowly, slowly, slowly, then speed up as they age out.  A new one certainly won't hurt, that's for sure.

    Your system has a diffusion high vacuum pump or a turbomolecular pump?  If a diffusion pump - when was the last time the diffusion pump fluid has been replaced? Too low diffusion pump fluid can cause odd problems.    How about the PM on the rough pump?

    Take a look at the videos on the link I shared. The how to clean the ion source guide was updated in 2021... (7) How to clean an Agilent GCMS Ion Source - Files - GC/MS - Agilent Community

Was this helpful?