Endrin Breakdown, need help

[MadAsAHatter]

I need some help reducing Endrin breakdown on GC-ECD instrument. The method I'm running specifies that the breakdown be 20% or less. I have made progress with it, at first it was in the 60-70% range & I've gotten it down to 35% and can't get it any lower. So far I've done the basics; changed the septa, liner, and gold seal, cleaned the inlet and clipped the column. I changed from Thermo liners to Restek blue sky liners, that helped. I read on here somewhere about dropping the inlet temperature, so I tried that. I went from 250C to 200C, that helped some more. I also tried some new standard in the off chance that our old standard broke down & had Endrin ketone and aldehyde in it. Changing standard didn't make any difference. I have made progress in lowering the breakdown, just not enough and I'm not sure where to go next. If anyone has some suggestion on what else I can do I'd greatly appreciate it. Thanks in advance for any help.

[osp001]

What's your carrier gas, and what does your oven temperature look like?

Looks like endrin breaks down at 200C; what happens if you run your injector lower than 200, maybe 175 or 180? You can always cook it out later if it turned out to be a bad idea.

[MadAsAHatter]

Carrier gas is helium.

Oven temp starts at 90C 20degrees/min to 150C then 10degrees/min to 290C. Endrin comes out about 245C, Endrin aldehyde at 255C & Endrin Ketone at 265C if that makes any difference.

I'll try dropping the inlet temp another 15-20 degrees and see what happens.

[osp001]

Restek has a pretty nice chromatogram including this compound. Can't figure out how to properly insert a link with an URL, but it's here:

http://www.restek.com/chromatogram/view ... 25/72-20-8

Column conditions: 120 °C to 200 °C at 45 °C/min to 230 °C at 15 °C/min to 330 °C at 30 °C/min (hold 2 min)

Don't know if that may help.

[MadAsAHatter]

I found these oven settings on restek's site http://www.restek.com/chromatogram/view ... /breakdown

Gave that a shot but no luck, I'm still at about 30-35% breakdown. Using the method above I did try changing the splitless time lower, but that didn't make much difference. Do you have any other suggestions of something I can try?

[osp001]

My "dumb looks are still free" would be derivatization. Safe and Hutzinger describe a method in Mass spectrometry of pesticides and pollutants from 1979 but I don't have a copy handy so I'm not sure what they recommend.

Given Restek's tech support a holler?

[Steve Reimer]

If you shoot some dirty sample extracts does the breakdown get better or worse?
Are you looking at DDT breakdown too?
If the DDT is great and the Endrin breakdown is bad a little 'conditioning' may be what it takes. This suggests that you have a reactive site or sites in your inlet that you haven't found.
Good luck!

[MCAbraha]

Could be your liner. We have had many issues with specifically Endrin and endrin breakdown issues. EDIT: to be specific, on our Varian-3800 on helium we would have immediate Endrin breakdown after calibration curve was ran resulting in 130-150% recovery for Endrin breakdown products in our CCV within just a few injections. That was with a Siltek-coated liner. We switched to a standard SGE splitless liner and that seemed to help enormously.

Alternately, that same SGE liner is likely the source of our issues on our Agilent GC (with different column types). I am planning on swapping it out this week with a free Restek liner that does not have glass wool to see if that helps.

I have heard glass wool can cause Endrin problems due to active sites on the increased surface area. Though the severity of this likely depends on other factors as well.

Also, is your injection port de-activated? We used Silco-steel injectors but that was a Varian 3800.

I'll be following this as we just recently started pesticide analysis on an Agilent and had issues with Endrin, Mirex and Methoxychlor. My thoughts are that it has something to do with our liner where one may work with one type of column but not with another. Will be swapping it out soon to test theory on the Agilent.

[MCAbraha]

Steve Reimer is on to something as well. If Endrin breakdown is rediculously high (30+%) while DDT breakdown is basically nonexistent then you may have another issue at hand.

Are you using a Pest Eval Mixture (PEM) to measure breakdown? Also, what type of columns are you using?

Could very well be that your PEM mixture has degraded, though unlikely. Do you have another GC to confirm on?

Also, if you run a 2nd-source CCV does Endrin Aldehyde recover high while Endrin recovers low?

Just curious.

[MadAsAHatter]

I haven't been able to make any more progress on the Endrin breakdown situation as the instrument broke last Thursday & now needs repair (yet again). Don't know what happened but the split flow rate & split valve on the instrument stopped communicating with the program and the tech I talked to said the whole injection port module needs to be replaced. I guess some of the electronics in the module went out. By the way, I'm running on a Thermo Scientific model Trace 1310 that's only about 2 years old.

We only look at Endrin breakdown for this method (EPA 505) and not DDT. I was starting to work on running a standard with DDT & Endrin to compare the breakdowns & also try different liners but didn't make it that far before the instrument went down. For now I'm at a standstill until the module gets replaced. I'll let you all know how things go once I'm back up and running. Thanks for everyone's help so far.

[Bigbear]

What do you mean by cleaning the inlet? I run EPA 525 and need to abrasively clean my inlet periodically. Agilent has a gun brushing application that I tried but did not like. Instead I have extra inlets and just swap them out, then clean the dirty one with the alumina powder I clean the MS with. I also replace the split vent line ( don't forget this step).
I use a Restek direct connect liner with the hole at the top. I also use a pulsed split less injection. When everything is clean I get <1% endrin and DDT breakdown.

[MadAsAHatter]

Bigbear,

Yes, I did Agilent's gun brush method except I used cotton swabs instead of the wire brush.

I really wish I could have some extra inlets on hand and just swap them out and clean the dirty one like you do. I can't even change/clean the split vent line or split valve. The way these new Thermo instruments are designed, everything is contained in a module. You're not able to remove the inlet, or even get to the split vent line or valve. To do any of that you have to replace the entire module. I sat on the phone asking our Thermo tech if there was any way to do it and they said nope the whole module would have to be swapped out.

Like I said the module went out and has to be replace anyway so at least everything will be clean and new.

[Bigbear]

That's not a good design for an inlet! In your case I would use the gun brush technique, as I doubt a Q tip with solvent would do much cleaning. For Agilent inlets they recommend a 38 caliber brass brush ( don't use the SS ones some chromatography suppliers sell).
Next I would make sure that the liner will contain all the vapor from your injection , also consider a pressure pulsed injection to contain the solvent vapor.

[BMU_VMW]

Since you have a 1310, wouldn't it be easier to install a ptv and inject at lower temperatures and than heat things up?
If I'm having trouble with endrin breakdown I simply change the liner and when nescessary the pre-column and I'm up and running again.
( we analyse pesticides in water using a liq-liq extraction with dichloromethane, injecting 50µl of extract at 25µl/sec in a liner with sinterd glassbeats)

[James_Ball]

That's not a good design for an inlet! In your case I would use the gun brush technique, as I doubt a Q tip with solvent would do much cleaning. For Agilent inlets they recommend a 38 caliber brass brush ( don't use the SS ones some chromatography suppliers sell).
Next I would make sure that the liner will contain all the vapor from your injection , also consider a pressure pulsed injection to contain the solvent vapor.

I was told a 32 caliber brush works better and not so tight, but they are not as easy to find except in a gun shop. Bronze or brass brush as you said, not stainless steel, that is too abrasive and will scratch the inlet. Of course for a Thermo inlet, you have to figure out the exact diameter before getting the brush.

One source of breakdown we always had problems with was contamination at the port where the split exhausts from the injection port. If you get a buildup at that hole, it can cause breakdown even though it is outside the glass liner. If there is no way to clean that, even if only to backflush with solvent, then it truly is a poor design for a split/splitless inlet unless you will only ever run calibration standards.