Define type of detector first.

Did you checked if column is properly installed to the injwctor and detector?

You don't have any fkuctuations in gas line pressure?

Regards

GB

Grzegorz Boczkaj thank you for the response. I believe the detector is a 5971 series mass selective detector. The column should be properly installed because we actually replaced the column and there was no difference in signal to noise ratio before and after the replacement. Is the gas line pressure the pressure of the carrier gas? If so, then there are no fluctuations in this pressure.

John S Wishnok

There is nobody at the company who is an expert in using the GC/MS. This is because it is old and has not been used in a while. The detector is definitely a 5971 mass spectrometer. I ran a sample of 50/50 IPA and Ethyl Acetate and noticed that the noise only happens when looking at the spectra for the peaks. There is little to no noise in between, before, and after the peaks. Does this mean that the mass spectrometer is working fine, and that something is dirty in the GC? I cleaned out the injection port and replaced the liner, but this did not make any improvements. Our next step that we can think of is to buy a new column.

I have attached an image of the instrument settings.

I have also attached an image of the system, along with the spectrum of IPA. The top graph is the total ion count, while the bottom graph is the spectra at the peak.

Like you said I understand if it is hard to troubleshoot on here, but I am just looking for any suggestions.

Thank you.

A 5971, that's old. I worked with a 5970 30 years back.

I do see what I quess is a solvent peak, what solvent did you use to dilute iso-propanol, ethyl acetate and 1-hexanol? ....... Wait I see that your sample is 50/50 IPA and ethylaceate........ what !!!!! That is not a sample, that's pure solvent. That is way, way, way, way (times 10) to much. You are massively overloading your detector, of course you will not see a good spectrum.

First try to dilute some alkanes like octane, decane, dodecane in hexane (as a solvent). Concentrations around 100ng in 1µl solvent (100mg/l) and inject 1µl, splitless or with a split up to 10. That should give some nice peaks.

I see you scan range is mass 20 to 450 or something like that, change it to 29 to 300. You should go for a scan speed of 4-5 scans/second. Try to set the solvent delay time after the solvent peak (a couple of minutes).

Did you do an autotune to tune the MS (calibrate the mass scale and detector sensitivity)? I don't know if that is an option on a 5971 but look for it.

"Online discussion threads may not be the best way to do this."

I agree with Pete, find someone with experience and I think it is time for an upgrade to brand new 5975 and a couple of days GCMS training.

Alex Van Renesse thank you for the response. We ordered a new column because the one currently in the GC is old. I will try octane in hexane once we replace the column.

Yes, I do run an autotune on the MS. Also, I pump the MS to operating pressure at the beginning of each day that I use the MS. I always let it pump down for about 4 hours before using it, like the manual recommends. When I turn the system on I do always hear the rotary pump start up.

I only have a couple weeks left at the company. As a result, I am going to try a diluted alkanes, after we replace the column. If this does not improve the spectrum, then I am going to have to relay all the troubleshooting information that I have collected to the next intern and he/she will have to continue.

Thank you to everybody who has given suggestions.