Noise from TD-GC-MS Chromatograms

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

2 posts Page 1 of 1
Hi everyone, first time poster here.

I'm a second year PhD student working with ambient air samples and analysing them via TD-GC-MS. (TD, Markes TT24-7; GC, Agilent 6850; MS, Agilent 5975C; running MSD ChemStation G1701EA). Ordinarily, the instrument has been running just fine with only a few issues to iron out here and there, but after having shut down the instrument and transported it to another institution, things have become a little unstuck. I'm now using the TD-GC-MS to identify and measure SOAs from VOCs in an aerosol chamber. The VOC is injected into the chamber and mixed with a NOx (varying ratios of NO and NO2). The samples are analysed using the TD-GC-MS, and in theory we're supposed to be able to measure VOC decay and oxidation products.

My instrument is designed to operate quickly in an aircraft, so it is equipped with a two-trap system. This allows one trap to be sampled whilst the other is sampling. At the beginning of a sample run, the sample is taken, sent through a glass cold finger (cooled to -30C by a sterling cooler) to dehydrate the sample, collected on one of two traps, passed through the GC column and analytes detected in the MS.

With recent sample runs, I've had a lot of noise appear on every other resulting chromatogram. It's tempting to think that one trap is faulty, but I'm forced to think otherwise because the calibrations I run and the blanks all produce normal, expected chromatograms, and I only replaced the traps a few months ago. Some days, the faulty chromatograms produce a lot of noise around the baseline, but I can still detect a major peak easily. Other times, so much noise is produced that the entire chromatogram is useless.

I've tried shutting down the TD software and rebooting it. This worked once, but the issue returned the following day. I've done a full shutdown of software and instrument, but again, the issue returned.

I'm a complete novice when it comes to GC-MS, so any help would be greatly appreciated!

P.S. I've tried to upload photos, hopefully it'll work!

https://flic.kr/p/QMFaKN
https://flic.kr/p/QMFahy
It'd be interesting to see what the spectra look like from the noise peaks. My money is on a lawn spectra as this looks like an electronic issue rather than any sort of contamination from your traps
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