No peaks

Question

Hi, I've been using GC6890N/MSD5975C with no issue but after I recently performed tune evaluation, suddenly the sensitivity decreased severely and there was no peak detected unless very high concentration like 10% loading. Auto tune was fine every time I tested. I do manual injection, so not relevant to ALS, etc.
So, I followed the troubleshooting guide. These are what was done so far;
- replaced septum, liner, o-ring, gold seal, ferrule in inlet.
- replaced ferrule in GC/MS interface
- removed guard columns, cut off ~1 cm of column at each side and re-installed column (same column) with new ferrules.
- cleaned ion-source
- replaced filament
While doing these, there was a leak issue but it got fixed, and auto tune passed.
Surprisingly though, I still have the same problem - poor sensitivity or no peak at all with small loading sample. Tune file was correctly saved and assigned.
Below is the auto tune report (please note the vacuum reading is not valid because the ion gauge is failing), and the tune views (number 24 is when ion source was cleaned).
Your advice would be very much appreciated. thank you

paulsalverda · Accepted Answer

You have a small air leak that should be fixed. 
 Did your peak's retention time move or just got really small but stayed in the right place? 
 Did you try squirting the sample from the syringe onto a KimWipe to make absolutely sure sample comes out? Plugged syringes happen all the time as do worn out plungers. 
 How far is the column installed in the injection port? Into the MS? How is your guard column connected to the analytical column? What happens if you install the analytical column direct into the inlet?

paulsalverda · Answer

Switch to Filament 1 - then save the tune as atune.u ... and then tune again. 
 Sometimes it is necessary to replace both filaments with new ones at the same time. The opposite unused filament is not glowing, but the electrons still go there and are reflected back. The electrons bounce back and forth four or more times. 
 Have the repeller insulators been replaced lately? Are they pristine white beautiful ceramic? What about the brown lens insulator, replaced sometime in the last couple of years? How about the PM on the rough pump - how old is the pump itself? What is the column flow into the MS during tune? Pumping/vacuum issues can cause strange tuning and results. 
 And just for fun - how many runs are on that system? 
 6890: Options Diagnostics Instrument Status

paulsalverda · Answer

The repeller insulators are ceramic. They're quite porous so sonicating in solvent doesn't help all that much. It won't hurt them but doesn't clean them enough. If your lab has a muffle furnace, you could put them in a ceramic crucible and bake them hotter than 500&deg;C...up to 1000&deg; C is fine for them. This cleans them well. Slowly heat up and slowly cool down, too or the thermal shock can break them. 
 The brown lens insulator is vespel so maybe some careful use of a cotton tipped swab dipped in solvent will help, but the recommendation is to replace it somewhat regularly. 
 It was originally sold in August 2007.

paulsalverda · Answer

Much can be gleaned from serial numbers. Yours was built in August 2007. That means 4,013 work days since then. How many samples has it run? How many times has the source been cleaned? The column replaced? The pump PM'd? 5,915 calendar days - how many revolutions has the turbo pump, which spins at about 60,000 rpm, turned? That's a fun calculation.... about 5,11 x 10^11 ! 
 The 5975C end of production was 11/30/2013. The End of Guaranteed Support was 12-31-2020. There are some parts that are either at incredibly low stock worldwide or even unavailable. There is no way to get new replacement electronic parts made for that model as those chip manufacturing processes are not even used anymore. The standard turbo pump TMH071 pump is obsolete - has it been replaced sometime by the Pfeiffer HiPace 80 (G3170-67000)-- about $9,000 USD of parts plus labor? The detector - the older EM is no longer manufactured --- has it been replaced sometime by the Triple Axis Detector version using the G3392A kit - about $4,500 USD of parts plus labor? 
 The upside is that there are still many of these out there running, but they are all coming up on at least ten years old. Electric fans, turbo pumps, and rough pumps all spin and spinning devices fail eventually. Sample residue deposits on all of the surfaces inside the vacuum chamber. They redistribute and dirty a freshly cleaned source faster the older the instrument gets. That requires remedial cleaning. 
 So ...it's complicated. The 5975C is at or quickly approaching the time where fixing it may not be economically feasible.

No peaks

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