Agilent 5890/5973 chromatography problems

[Omaejel]

I have an Aglinet 5890 with a 5972MSD. The chromatography is terrible for the early compounds. The last two compounds we use for internal standard look fine, but everything else comes out as blobs. I have attached an image.

We have replaced the column, proportional control valve valve, septa purge regulator, weldment, mass flow controller, and solenoid valve assembly. All to no avail. Any advice would be greatly appreciated.

http://www.flickr.com/photos/52187650@N07/4809631718

[bhuvfe]

Is it split or splitless?

Can you post also the oven ramping and give us a clue about the compounds you want to analyze?

Are the internal standards hyrdocarbons?

What kind of column are you using?

[Omaejel]

Sorry, I should have included more info. I don't know why in the world I didn't include all the other stuff initially. Here's everything:

I am analyzing compounds from the VOC 8260 list.

It is running split.

Carrier is Helium.

Column is a Restek 30m with .250 diameter and 1.4um film thickness.

Inlet temp is 200C. Inlet has had maintenance recently.(after the problem began) Liner is a gooseneck.

Column flow is 1ml/min. Split flow is 30ml/min.

Aux temp is 240C.

Oven parameters are as follows:
45C for 1 min.
Ramp 13C/min to 150C
Ramp 25C/min to 240C hold for 1 min.

Internal Standards/ Surrogates are as follows:
Pentafluorobenzene
1,4-Difluorobenzene
2-Bromo-1-chloropropane
1,4-Dichlorobenzene-D4
Dibromofluorobenzne
a,a,a-Trifluorotoluene
Toluene-D8
4-Bromofluorobenzene

When you look at the MSD library, the early peaks from about 3.5min-5min are the internal standards and surrogates and not just some garbage on the column. The last two peaks that look like they are good peaks are the last internal standard and surrogate (4-Bromofluorobenzene and 1,4-Dichlorobenzene-D4)

I can provide any other information you might need.

Thank-you for your time.

[bhuvfe]

Thanks for the info. I'm afraid I have some more questions..

What solvent are you using to dissolve your standards?

Are you sure that you have 1 ml/min as flow? I see that you start acquisition from 0.5 min and I don't see a solvent peak. A non retained compound (like air) should be around between 1-1.5 min if i recall correctly.

And is it possible that you have a mismatch between the polarity of the column and the solvent? (by the way, which type of Restek column?)

Has this method ever worked on your system?

What are the theoretical concentrations of the standards in the picture you posted?

[haiedc]

You probably have something wrong with the inlet/solvent/injection technique.
To try, you can increase the split ratio, reduce the injection volume, move to lower bp solvent etc...

[Omaejel]

Methanol is the solvent. We typically cut the solvent peak off by not turning the MS filaments on until after it has eluted.

The column is a Restek VMS-RTX if I am not mistaken.

This method used to work on this system and currently works on 17 other GC/MSD systems in my lab.

We normally use a purge and trap system to introduce the analytes, but I did a direct injection into the inlet of 1ul of internal stds and surrogates just to make sure the problem was not in the purge and trap. The chromatogram linked earlier in the message is the direct injection, but it looks identical to the ones made via purge and trap.

The concentration injected is the same amount that we put in all of our runs which is effectively 40ppb

[bhuvfe]

I'm not familiar with a RTX-VMS but I assume that is relatively polar.
The fact you get a similar broad-peak even with purge and trap seems indeed more a problem with the injection.

A similar effect is easily obtainable with a wrong splitless injection (e.g.with a splitless time too long, or with a oven T too high for the solvent used) or when you think you are doing split injection but in reality, due to a obstruction in the split vent, you are running splitless. Maybe check if you are in a similar situation.

You get quite a nice signal for 1ul of a solution of 40 ppb of your analytes for a split injection.

Are these really 40 ppb or have you already taken into account a "normal" concentration factor of the purge and trap?

Good luck.
bhuvfe

[Omaejel]

I will check the split vent for an obstruction. That seems the most likely culprit because this instrument has worked fine for a long time and has recently started giving the weird chromatograms.

After reading my last post, I can see that I did not make myself quite clear about the concentration. Taking into account that we inject 1ulUunlessJulyfullrulecouldfullyruleswould of internal standard/ surrogates mix into 5mlmlmilemilesmillionmultiplesmall of sample water and then run that on a purge and trap, the final concentration of internal standards in our sample is 40ppb. I injected 1ulUunlessJulyfullrulecouldfullyruleswould of internal standard mix into the inlet that is at a concentration of 200ppm in methanol. Sorry for the confusion.

Thanks for all the help!

I will post updates as i get new information.

[haiedc]

If the system had been working well for quite a time, then the method is OK. The problem obviously is from the inlet, so you can check the column installation, the liner, the split vent flow and the septum purge flow. I mean all the parameters related to the inlet.
Good luck

[Don_Hilton]

Looking at the the chromatogram you posted, the peak shapes on the front end look like an overloaded column. Would the mass range acquried include ions from the solvent? If not it might be worth expanding the mass range and making a run. I would expect the solvent tail to be very large in the region with the badly shaped peaks.

Following on the idea of a problem with the split vent. Have you changed the carbon trap on the split vent line? And how do intensites of peaks shown here (particularly the last two) compare to the same sample shot on one of the working instruments?

[AICMM]

Omaejel,

Your ugly peaks are all the ones normally sitting on top of your methanol peak while the pretty ones are clearly separated from the methanol. Couple of things I would try. I would increase my split flow (as suggested by haiedc) to see if that helps and I would measure my split flow while the purge and trap is desorbing just to make sure it is what I thought it should be. Second, I would look to replace the trap since it may be holding on to the methanol too long. Third, I would look at my desorb conditions to make sure they really match the others. I would especially focus on the desorb time since it appears to me that your "methanol peak" is more drawn out than I would have expected. Finally, I would look at the solvent volumes I am using to see if I am using more with this analysis than I might be with other analysis.

Best regards.

[MLyttle]

Have you checked your interface heater?

If the interface heater is no longer working, unplugged, or turned off, you will often see the earlier compounds condense on the column and give blobs similar to yours. The later eluting compounds look fine as the oven temperature increases.

Mike

[Omaejel]

If anyone is interested in this I am still having problems with this instrument. I have not come back to this one until now due to other, more pressing issues.

We had a 5972's electronics kick the bucket so I moved the entire GC from that instrument to this one and we are still getting the exact same chromatograms. Now I am more confused than ever.

The MSD interface is heating fine, so I don't believe that is the problem. Also, it's the interface from the other GC that was working fine with the other MSD (until the electronics died).