GCMS question

[labwork]

I installed a new column (with a guard column) and conditioned for about 4.5 hours. Then I connected it to MS, and run a very routine temperature program (up to 300C at one rate).

The system blank shows a big hump covering almost the whole range prior to the final stage (up and stay stable). This hump stays even after a few sytem blank runs. When looking into the hump, the mass spectrum only shows 28, 32, and 44. This is weird, because before and after the run, I checked the air leak and the tune page, and no air leak is shown.

Any suggestions will be appreciated. Thanks!

[Earl]

Check the ferrule connecting the column to the mass spec. What is likely happening is that your ferrule at the mass spec interface is leaking at elevated temperature. Usually tightening the nut a little more gets rid of this. If there is no leak at the mass spec interface the same thing could be happening at the injection port, which stinks because you may have oxidized your new column. Cross your fingers that the leak is at the mass spec interface.

[AICMM]

Labwork,

Integral guard column or one connected with a union or press fit? Also, no 207 ion which, if memory serves me, would be indicative of column bleed? If the leak is at the front, I would expect to see this as well. If not, then the problem does appear to be more at the back of the system than the front, which would be a good thing.....

Best regards.

[Consumer Products Guy]

28 nitrogen, 32 oxygen, 44 carbon dioxide. Any 40 for argon? Still sounds like air leak.

[labwork]

Check the ferrule connecting the column to the mass spec. What is likely happening is that your ferrule at the mass spec interface is leaking at elevated temperature. Usually tightening the nut a little more gets rid of this. If there is no leak at the mass spec interface the same thing could be happening at the injection port, which stinks because you may have oxidized your new column. Cross your fingers that the leak is at the mass spec interface.

Thanks for the suggestions.

I tightened the nuts on both ends quite a few times, and checked with a leak detector each time. I also checked it using the air check function in the tune page, but it seems no air leak was detected.

[labwork]

Labwork,

Integral guard column or one connected with a union or press fit? Also, no 207 ion which, if memory serves me, would be indicative of column bleed? If the leak is at the front, I would expect to see this as well. If not, then the problem does appear to be more at the back of the system than the front, which would be a good thing.....

Best regards.

Thank you for the suggestions.

I used a univeral press-tight connector. The 207 ion was observed at <1% of the base peak (ion of 28) in the mass spectrum of the hump. Along with this 207 ion, the 281 and 341 ions were also observed at <1%. I think these ions are normal column bleed, which also appeared at greater abundance near the end of the run.

[labwork]

28 nitrogen, 32 oxygen, 44 carbon dioxide. Any 40 for argon? Still sounds like air leak.

That's why it's frustrating. Thanks for the comments. The ion 40 is also observed at about 3% of the base peak (ion of 28) in the mass spectrum of the hump, which is slightly lower than the intensity of the ion 44. I've checked air leak using the leak detector and the check function in the tune page.

[AICMM]

Labwork,

What is the abundance of 32 relative to 69 in your tune file?

Best regards.

[JI2002]

Are you using hydrogen as carrier gas? Why do you scan down to 1, is this just for ha-ha or it's really neccesary? Run a balnk by scanning to 35 and see if it makes any difference.