Chromatography Forum

I work with a PE Autosystem XL/Turbomass Gold. I've been having a recurring contamination situation in the last 3 months or so, but I can't seem to figure out why. It happens everytime I clean the liner.

I remove the liner with MeOH cleaned tweezers, remove the glass wool, and then sonicate it in DCM. I wear a brand new pair of nitrile gloves everytime I do this. Then I insert new glass wool, and a new o-ring, and then put it back into the injector. For the septum cap, I remove the septum, wipe out the inside of the cap with a MeOH-soaked kimwipe, and then insert a new septum. Once finished, I have to run many blanks to clean up the mohawk of peaks that results.

I've tried using different glass wool, incase mine is contaminated, and that didn't solve the problem. The contamination has alkane distribution (m/z 57, 71, 85, etc.) which suggests grease maybe? I've also noticed that when I clean the septum cap, there is some black greasey stuff inside the cap that I wipe out. I've tried sonicating the cap in DCM, MeOH, and Et2O, but nothing helps. I've used these solvents on the quartz liner as well.

The contamination is significant. If I run a 4ppm PAH standard immediately after cleaning the injector, the mohawk of peaks are larger than the PAH peaks.

Any ideas?

Rosie

I sympathise, I get something similar.

Do you have to do an injection to get the alkanes ?, or are they there in a programme blank ? If they need an injection they might be coming from the syringe, but that would not explain the connection to an inlet clean.

You need to break the operation down into single steps. Remove the septum cap, remove the septum, wipe out and put the old septum back in again (you know its clean).Run.

Then put in a new septum. Run.

Pull out the old liner and put it back in again, remove the old liner and repalce with one with no glass wool, . etc etc. Tedious but necessary.

Cut a piece out of a new glove, extract with some clean solvent and inject it on a clean system.

The black gunk is a concern, where exactly is it in relation to the septum ?

Good luck Peter

Hi Peter,

Thanks for your reply. I'm glad to hear that I'm not the only one with this type of problem.

That's an interesting thought about the blank. I usually perform column blanks by injection from an empty vial. I will try running a column blank without injection to see if I see these compounds.

I see what you're saying about breaking it down into small steps - good idea.

As for the black gunk, it is between the sides of the septum (not top and bottom) and the ridges on the inside of the septum cap. And it's there everytime I clean the injector, which is about every 60 runs of PAH standard for my current experiment.

Thanks for your suggestions!

Rosie,

Split or splitless? Sounds sort of like the old 5890 problem of getting stuff in the splitvent line.

Best regards.

I'd also try another brand of septum, or soaking/ultrasonicating one of your septa in solvent and analysing the extract. I'd also try baking the cleaned insert and septum cap before installation. Make sure you are not blowing the solvent out with compressed air, it's a potential source of alkanes.

I'd also agree with AICMM about muck in the vent ( or septum purge line - if your toy has one ), and that's much more of a mission to clean, but may be necessary..

As Peter notes, these issues require a systematic approach, and please let us know how you finally solved, if other than by a career change.

Please keep having fun,

Bruce Hamilton

I am running splitless. What do you mean by "getting stuff in the splitvent line?"

Thanks.

I'm afraid that a career change is not an option.

I've never dried the liner with compressed air, I clean it with DCM - which evaporates almost instantly.

I will try an extraction of a septum as you say. I recently switched to high-temperature septa, but I'm pretty sure that this problem began before that.

Thanks so much, everyone, for the feedback!

Good to read that you're not contemplating a career change

As your problem is after cleaning, it's possible that your cleaning solvents are introducing something ( or liberating alkanes from the black gunk).

I assume your DCM is fresh, with very low residue, and pure grade without 2-methyl-2-butene inhibitor ( which although having a similar boiling point to DCM, also can readily form much less volatile compounds - especially in older bottles of DCM ).

Just to be sure, I'd take a few mls of DCM and evaporate to about 100 ul ( almost to dryness ) and analyse that for alkanes.

I'd still also heat DCM-cleaned components in an oven ( use GC oven ) for a few minutes to remove any medium volatility material.

Please keep having fun,

Bruce Hamilton

The DCM isn't the source of the problem. It's distilled-in-glass grade. Also, the alkane problem was prominent before I started using DCM to clean the liner. I used to sonicate the liner first in Et2O, and then in HPLC grade MeOH. I was later told that DCM would work better, so I switched. I thought it might resolve the current problem. No such luck. I always only use high-purity solvents for anything to do with the GC/MS to avoid problems - go figure!

I will heat solvent-cleaned parts in the GC oven before reinstalling. Great tip!

Hi Rosie

I've never used (or even seen) the model of GC that you have. It is possible that the black gunk is coming from the samples - possibly getting deposited there due to excessive solvent vapour volume when you do a splitless injection. Do you have a septum purge, and if so what flow is coming out through it ? What is your sample solvent, and how much are you injecting ?

Peter

Peter:

I wouldn't advise anyone to use this system. I've been working with this very expensive paperweight for over 2 years and have had nothing but problems. We've had just about every board in the GC replaced, but we still get weird electronic problems with it.

I am experimenting with different injection solvents (high boiling alcohols), and their effect on PAH response. I've been injecting toluene, isooctane, 1-butanol, 1-pentanol, cyclopentanol, 1-hexanol, 1-octanol. I perform 2µL injections in splitless mode. Optimized injector T = 360°C. Septum purge = 4mL/min.

Hi Rosie

360C is pretty high for an inlet temp, and if the inlet is designed to maintain a uniform temp from top to bottom the septum will be suffering, although I would be surprised if it was shedding alkanes. You need one of the really high temperature septa, they are quite hard and you do not get many injections out of them but at least they should not crud up your samples

Peter

I am using high-temperature septa and o-rings. My operating temperatures do not border the upper temperature limit of either.

Rosie,

Does all of this happen with a brand new liner?

After how many blank runs you have a clean baseline?

Maybe you can bake your inlet using a high split method (>100:1) for an hour or more.... and then try again your usual method to see if it improves the situation.

Regards,

Bhuvfe

Hi Rosie

How about the gloves ?

As an outside thought - if you have hydrocarbons on your forceps rinsing them with methanol is not going to help much. Try a non-polar solvent or even better the microbiologists trick of heating them to red heat in a flame (not near the solvent through !!).

Peter