Injector port settings and tuning question

[acrolein]

Hi,

Can anyone tell me the proper settings for a a HP5890 GC Series II GC split injection port with respect to: injection port temperature, split valve on/off time, scan rate, and proper flow. We run volatile methods by EPA8260C so we'd be looking for early eluting gases (bromomethane, chloroethane, etc) and late eluting dichlorobenzenes and naphthalene. Right now, we have a Agilent DB624 column 25m .2mm ID and we have the injection port temperature at 210 deg, the split ratio at 30:1 (flow into the column at 1ml/min) and the split valve scheduled to turn on at 1 minute and off at 2 minutes (we are interfaced with a Tekmar 3100 Purge and Trap Unit to transfer sample to the GC). Basically, we are getting peaks that either show signs of fronting or tailing. We've tried to adjust flow with no great success either way.
Also, with regard to tuning, after source cleaning, we get good ratios 69/219 at 50% and 69/502 at 3% with EMV at 1700. After a few days, tuning becomes erratic (can't get good ratios) and EMV jumps to 1900+. It would indicate a dirty source, and indeed after a few days, I took the source out and there was an inordinate amount of burn on it, even more than you would expect from fairly aggressive tuning over a 3 day period. Anybody have any ideas as to what the issue would be with that? I should also mention that pervious to this my boss had suggessted leaving the split vent valve constantly "on", so I don't know if that would be contributing to the dirty source. I know this is a lot, so any help would be greatly appreciated.

[AICMM]

Acrolein,

An injection port at 210 should be fine. The whole run is done split (purge A on with a 5890) which has the effect of greatly reducing the water into the GC/MS. I've tried the splitless/split routine as well and it basically does not work. You put way too much water onto the column and the gases end up looking terrible, worse than just running split.

Your flow might be a tad bit too high for a 0.2 column and is probably too high for your diffusion pump (see earlier posts.) This may contribute to issues with the heavier compounds. 30:1 split is good for the trap but you can probably get away with a little less (20 or 25:1) and still get good desorption and better sensitivity.

Regarding tuning, forget 502 except as an indicator of source cleanliness. You really should focus on 131 and 219 since this is the mass range of BFB. Pay close attention to peak widths (again, see earlier posts.) Regarding source burn, my first guess would be water. If you are running splitless, you are putting a significant amount of water on column and this ends up in the MS. Water is very hard to pump out (notice how long it takes to get rid of when you pump down?) which my be the source of contamination over the short time. You should get weeks between tunes and months between cleanings when running volatiles, if everything is set up right.

Best regards.

[acrolein]

Thanks, I'll apply your suggestions. One other thing, if I may. Our BFB tunes are showing a larger than usual abundance of 75, 79 and 81 ions. The 75 ion is over 70% and I used to use that as a benchmark for when I need to clean the source, but admittedly, I've never experienced a problem with the 79 and 81 ions at the intensity that they are at (which is about 40-50% of mass 95). Do you have any thoughts as to what the problem with that might be? Thanks again!

[AICMM]

Acrolein,

You are saying that 78 and 81 are 50% of 75???

Best regards.

[acrolein]

AICMM,

The 79 and 81 are 50% of mass 95. It looks like the intensities of those ions plus the mass 75 intensity are greatly increased from what they usually are. No matter if I manually tune or autotune, when the BFB is run, those 3 ions are high, especially the 75, which causes the BFB to fail.

Thanks again for your help.
Tony

[AICMM]

Acrolein,

First, what does a background scan look like, say 5 scans before the peak? Second, what is the 100 ion ratio and the 131 ion ratio compared to 69 in you autotune or manual tune? Third, what are the peak widths for these three ions? Fourth, how much 18 do you have compared to 69 ion?

Can you post your BFB apex spectra?

Best regards.

[JI2002]

Also post a tune file report if you can. What does it look like if you ramp the parameters such as ion focus, repeller and entrence lance? Can you post those too?

[acrolein]

I ended up cleaning the source again for the third time in 2 weeks yesterday and also changed out the foreline pump oil. We had been running our Tekmar P&T with a TurboCool option, so the trap was being cooled to 10 degrees. I have now turned that option off, thinking that maybe some moisture might have been getting into the trap that way. Anyway, I did a BFB tune this morning and other than the background being a little high, everything looks normal again. The 75 mass is at 51.6%, the 79 and 81 masses are about 5-10% of mass 75 and the sensitivity is great. So, I'll monitor it today and see if it holds, but it may be a combination of those 3 things that has it working again. Thanks again for your help with this.

[acrolein]

Well, sorry to say that although my peaks are good and we seem to have eliminated the peak fronting, tailing and sensitivity issue (using a flow now of .5ml/min and a split of 25:1), I'm still seeing a deterioration in my tuning over a 48-72 hour period. The day after cleaning the source, I was getting a good manual tune, with good ratios and low EMV (~ 1700). After a couple days, the tuning is erratic, EMV goes up to 2300 and BFB shows a high m/z 75 and 174. Basically, it does not seem tuneable. With regards to 502, I can autotune one minute and the 502 will be at 3 or 4%, a few hours later after a couple failed BFB's, it will autotune at 10-15%. I would suspect an electronic problem but after source cleaning, it looks good for 24 hours....it seems to be after a day or 2 of running when this happens.
As mentioned in a previous post, I have taken steps to eliminate the water by turning off the turbocool option on my Tekmar and increasing the dry purge time to 4 minutes. I should note that I have recently discovered that when I download a method to the GC, even though I specify the split ratio in my method, when I download it, the split ratio displayed on the GC (when accessing it on the keypad) shows a split of 0.00:1 and a split of 0, again, this is after downloading my parameters to the GC...every other parameter transfers correctly, so now I don't know if that could be part of the problem?
Sorry for all the posts, but it's getting a little frustrating and Agilent is giving me an "out of support life...can't really help" line when I e-mail them. I appreciate the feedback here. Thanks again.

[AICMM]

Acrolein,

The improved peak shape is expected. As long as you have right flow out the split vent line and purge A or B is on, then you should not really worry about the keypad reading. Regarding the tune instability, turn off the PFTBA valve in the tune and look at the air and water values to make sure you don't have a leak. 71's and 72's are difficult to seal with the O-ring along the top so I find there is often a leak somewhere in that seal. If that data looks good, the next place I would look is at "dipping" the quads. There should be a section in your manual that talks about this. I have done this a few times, and in one particular case it made a huge difference in system stability.

Finally, regarding Agilent and out of support, lots of third parties will be happy to separate you from your money offering service and support for this work horse system.

Best regards.