Repeller values creeping upwards of mid-30s

[mhyang]

We use Agilent GC/MS's (6890 GC / 5973, 5975, and 5977 MSD). The repeller values keep creeping upwards and now at least half of our instruments have the value in the mid-30s. For a particular instrument, what I've checked so far:

PFTBA present
Filaments are practically new
EMVolts 1247
peak widths of 69, 219, and 502 are within 0.59 - 0.60 ( with good abundance)
Good vacuum
Blue wire is in the back

The repeller is coming in at 34.81 (good gaussian curve during autotune; it's smooth)
Ion source cleaned (alumina slurry + sonication with DI water, MEOH, acetone, hexane)
Repeller is in good condition (no discernible scratches)
Ceramic insulator sleeves for repeller are new & uncracked

Tune eval is passing but I cannot get the repeller back down to the 20s range. Any ideas / advice is welcomed with open arms.

[kubowicz.tomasz]

Hello

I'd try to clean repeller with abrasive paper that comes with MSD kit (green sheet) and then sonicate it with solvents (from acetone-methanol-IPA-hexane).

Sometimes if you have N2 and O2 > 2-3% repeller voltage is higher as it needs more "power" to push ions through Quad.

Regards

Tomasz Kubowicz

[tangaloomaflyer]

Strange. I use aluminium oxide slurry and it usually works. Tomasz - when I use the green paper I'm left with a matt finish on the repeller. I always thought that the repeller should be shiny, or am I wrong?

[Ian_R]

Something is dirty. If it's not the source then it must be something further in. lenses (If there are any ? ) or the quadrupole itself.

[James_Ball]

The peak of the repeller ramp curve can be adjusted by adjusting your emission current. When the 5972 first came out and it had the adjustable emission current settings a tech from Agilent showed me that to bring the peak of the curve back down to roughly 18V you had to adjust the current on the filaments.

Pretty much every instrument I have has a different setting on the repeller so it isn't terrible if it goes up to 30V as long as everything tunes as it should.

Using the green paper and having a mat finish is what Agilent recommends as the cleaning procedure, but I do prefer to polish the repeller and other lenses to a mirror finish because it seems to help them stay clean longer and makes them easier to clean the next time. I have had instances though where I had to use very rough emery paper to remove a good bit of material then use finer and finer paper to bring it back to a mirror finish when the source became very contaminated. Scientific Instrument Service may still sell what they call "Shark Skin" polishing cloth that comes in a large range of grits topping out at I believe 12000 grit that almost feels like leather, and you can use those with a wet sanding technique to make the lenses look like mirrors if you work at it. The 5973 and newer instruments don't seem to need that level of polish like the older ones did, but it doesn't hurt as far as I know.

[mhyang]

Good to know; thanks everyone for the input!!