5977 tuning issues

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

10 posts Page 1 of 1
Hi all,

I have been running a new 5977B recently running low level PAHs, using DFTPP criteria in method 8270C, 8270D, and 8270E. I could easily get DFTPP to pass day after day, sometimes I would have to do normal tweaking of lenses, peak widths, etc. My chromatography was a bit poor, especially for the heavy PAHs. This was odd because I run a 5975C with identical conditions, with virtually no peak tailing.

So I decided to open everything up. I swapped out the Zebron column for a Restek Rtx-5Sil MS, and I cleaned the source. That's when I discovered the 3mm drawout plate. So I swapped it for a 6 mm plate because I knew it would give me better PAH peak shape.

Now my chromatography is great, but I can't get a tune to pass. Problem ions are 68 and 441. Peak shape in manual tune profile view shows significant fronting of 414 and 502. Tune evaluation shows 502 precursors at 10%, which is acceptable by the evaluation guidelines, but I know it's not good. My 5975C is at 2%.

I have now cleaned and reinstalled the source 3 times and I cannot improve peak shape for 502. Not sure what else to do...
Regards,

Christian
cjm wrote:
Hi all,

I have been running a new 5977B recently running low level PAHs, using DFTPP criteria in method 8270C, 8270D, and 8270E. I could easily get DFTPP to pass day after day, sometimes I would have to do normal tweaking of lenses, peak widths, etc. My chromatography was a bit poor, especially for the heavy PAHs. This was odd because I run a 5975C with identical conditions, with virtually no peak tailing.

So I decided to open everything up. I swapped out the Zebron column for a Restek Rtx-5Sil MS, and I cleaned the source. That's when I discovered the 3mm drawout plate. So I swapped it for a 6 mm plate because I knew it would give me better PAH peak shape.

Now my chromatography is great, but I can't get a tune to pass. Problem ions are 68 and 441. Peak shape in manual tune profile view shows significant fronting of 414 and 502. Tune evaluation shows 502 precursors at 10%, which is acceptable by the evaluation guidelines, but I know it's not good. My 5975C is at 2%.

I have now cleaned and reinstalled the source 3 times and I cannot improve peak shape for 502. Not sure what else to do...


I had trouble with these on my 7000C and had to widen the peak widths out to 0.8 in profile mode before these would drop to acceptable levels. I think the resolution is too high on these newer models and if you get for example 68.1, 68.7 and 69.0 then the two 68 peaks get added together in the check when the 68.7 should be part of 69 instead. Widening the peak widths lowers the resolution which doesn't need to be that high since you are not doing accurate mass work and it behaves more like the older models.

I have the extractor source in the 7000C and just ordered a 9mm extractor lens(equal to a draw out plate on normal source) and am going to try that for our PAH methods. There is a blog post on Restek dealing with that so I am giving it a try, I will see soon if we have the same problems with tunes.
The past is there to guide us into the future, not to dwell in.
Another issue is when running an autotune, then generating the tune evaluation, 502 is less than 2% of 69. All other instruments we have are well over 8%, some over 10%. Why I suddenly can't get adequate 502 on a relatively new instrument is very strange. I've never seen anything like it.
Regards,

Christian
Just a thought. With the larger drawout maybe we should use lower emission current. Lower emission current will increase the high mass and lower the low mass. It will also make the filaments last longer. On a normal source used for 8270/8260 I normally lower the emission to 25mA or less. Look at the repeller ramps, if they max out at the max volts then you can lower the emission current. They should reach a peak before max repeller volts at least for 69 and 219.
The past is there to guide us into the future, not to dwell in.
I will try to lower the emission. I may swap out the 6mm plate for the 3mm. Ever since I took the instrument down to clean the source, I cannot get 441 or 68 to pass for DFTPP. Peak shape in profile continues to look awful, with fronting for 69, 219, and 502. 502 looks the worst.

New problem - Now I'm getting an awful baseline, ions 207, 208, 209, 281, 96, 133, 44. Library search suggests polysiloxanes, column..
Regards,

Christian
cjm wrote:
I will try to lower the emission. I may swap out the 6mm plate for the 3mm. Ever since I took the instrument down to clean the source, I cannot get 441 or 68 to pass for DFTPP. Peak shape in profile continues to look awful, with fronting for 69, 219, and 502. 502 looks the worst.

New problem - Now I'm getting an awful baseline, ions 207, 208, 209, 281, 96, 133, 44. Library search suggests polysiloxanes, column..


That does sound like column bleed with those ions. If the column is bleeding it could be affecting the tune also.

Did you use a volt/ohm meter to check the source and make sure it was not grounded between two lenses? If an insulator is bad somewhere it could be throwing off the voltages and making the tune look bad.
The past is there to guide us into the future, not to dwell in.
I did not use a voltmeter, but I'm confident the insulators are good. The instrument is relatively new, and I've already changed the repeller insulators with no change.

It's been suggested to me by our tech to run the source at 230 and quad at 150. I've been running 5975s at 300 and 180 for years with great chromatography for heavy compounds. Just ran a test today with the two temps, and benzo (b,k) fluoranthene baseline resolution jumps from 77% to 93% by increasing the temperatures. Benzo(ghi)perylene tailing changes from 2.23 to 0.97. I don't understand why I should turn the temps down to help improve ionization in the source. I don't think it will improve.

We had another instrument with similar history, we cleaned the source, put it back together, and it's never been the same since.
Regards,

Christian
One thing that I have done that makes them really act weird and it is easy to do is get the Ion Focus and Entrance Lens wires reversed when reinstalling the source. The wires are labeled at the ceramic board and they are blue and orange, just have to make sure the Entrance Lens is the one closest to the quads.

Increasing source temp will improve tailing and separation but also lowers the sensitivity somewhat. Too cold can hurt sensitivity since more analytes can stick to the source so it is a trade off and you have to look for the sweet spot for each particular analysis.

Does the 5977 with your source have the spring loaded cone at the end of the transfer line that seals against the source? On the 7000 I normally have to remove that and check the position of my column tip to make sure it is not going too far into the source. I like it just barely 1mm beyond the end of the interface, then I replace the cone. I tried pushing it back but there just isn't enough room in the analyzer for my hands to do that and still see the end of the column.
The past is there to guide us into the future, not to dwell in.
I always ensure my ion focus and entrance lens leads are in the correct position. My coworker reminds himself by "B for Back" (blue wire in the back at the entrance lens).

You have me curious now about my column installation procedure. I wasn't aware the tip on the transfer line is spring loaded. I may actually have the column installed too far into the analyzer. I'll be checking that today. Should I be installing the column differently with this cone? And what is its purpose?
Regards,

Christian
The 5975 had a similar tip when using CI that you had to install for CI source and remove for EI source. I think on the newer models they just leave it attached and altered the EI sources to work with it.

Two setscrews hold it in place, and when removed the interface looks just like the older models. If you do a visual install and push it past the cone, then probably too far in. I always did it visually on instead of using the measuring tool, even on the 5973. For the 5973 I would hold one of the ceramic wafers over the end of the interface and push the column in until it hit, then tighten the nut and it left it about 1mm inside the source. With the glass front analyzers you can just watch it as the tip emerges instead of by feel.

The 5970 and 5971 had a hard stop at the end of the interface and you just installed until it hit and backed up about 3mm. The 5972 was the same except the tip was open, and first time I installed one I did it the same as the 5971, which put the column end all the way across the source chamber, it gave very poor peaks and sensitivity. Once I got the length right it ran great, so now I always check them visually.
The past is there to guide us into the future, not to dwell in.
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