baseline shifts in GCMS

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

7 posts Page 1 of 1
Image

Has anyone seen anything like this? These are post-maintenance runs with the needle removed to check baseline. Full scan 35-500, with threshold at 100.

System specs:
Agilent 6890N with 5975 iMSD
inlet: split liner (changed every 300 injections) with 20:1 split, new septa, 250'C
column/oven: constant flow @ 1ml, DB-1MS (newly installed and conditioned at 325'C for 2.5 hours after air/water passed), 150'C initial temp, hold 1 min, with 21'C/min ramp to 276'C and hold, post run ramp to 325'C for 3 min
MSD: source 230'C, quad 150'C, transfer line 230'C, baked out for 90 min following column conditioning.

Any ideas on why this is happening would be greatly appreciated!
What ion masses are showing in the spectra of that high background?
The past is there to guide us into the future, not to dwell in.
Image

high background v. drop in background. Everything seems to stay the same and just drop abundance. Unfortunately, I don't know if the 44 m/z abundance is normal for this machine because we usually only scan 50-550 m/z.

I thought maybe was a misaligned column, so cut both ends and replaced gold seal and inlet liner... Now 219 and 502 % abundance are failing on the tune and the dropping baseline problem remains :cry:
44 m/z is from CO2 in the system, the 207 and 281 m/z are from column bleed.

3500 counts is not a very high background at all. The dips could simply be flow pulses during the oven temperature program or some moisture coming from the head of the column and passing through, which is not detected but can suppress the signal( or methanol if that is a solvent you use).
The past is there to guide us into the future, not to dwell in.
Go to manual tune and scan. How many peaks are there?
Regards,

Christian
The drops in baseline were still present when we blocked off the MS with a no-hole ferrule. Cleaning the source seemed to resolve the baseline issue and tune. Thinking it must have oxidized to some extent when the vacuum pump failed.
I asked a similar question a little while ago so you may find this topic useful: viewtopic.php?f=3&t=87454

44 m/z is a common background ion on most systems.
7 posts Page 1 of 1

Who is online

In total there are 10 users online :: 1 registered, 0 hidden and 9 guests (based on users active over the past 5 minutes)
Most users ever online was 599 on Tue Sep 18, 2018 9:27 am

Users browsing this forum: Majestic-12 [Bot] and 9 guests

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry