Baseline dead flat but signals present

[pimezon]

hello all, we have a shimadzu GC-MS that we brought five years ago. Presently I am having an issue with the GC part I believe. The baseline is dead flat though I do see signals corresponding to components in the mixture. The RTs are pretty consistent but the dead flat baseline bothers me. Can anyone think of a possible reason for this? also any idea to solve this will be great.

I don't have the chromatograph to upload now, but will do that w/e I get hold of one next.

hope i can figure out what the problem is.
Thanks.

[Don_Hilton]

Based on expeerience with another type of instrument, I'll suggest a place to look: Does the data acuisisiton have an acquisition threshold below which it rejects signals as noise? If so is it set too high, rejecting those signals you normally see as noise? (On the instrument I used, I preferred to turn off this feature to ensure I got an accurate measurement of baseline for quantifying analytes - and the files were huge (for files back in that day...))

[DSP007]

Hello.

Highly probable hardware technical problems!
Especially if the ions m/z 16-40 are not visible in the scanning mode

Check for attached to the device test method - doth device?
1) the entire system
For the next test should detach chromatograph from the spectrometer
No fanatism "If not sure, do not overtake. Popered Batko (in front of his father) Batko in hell do not go"(с) (:twisted:
2) Separately, the mass spectrometer
3) Separately chromatograph

[Don_Hilton]

Before taking apart the GC/MS system - Check to see that the spectrum shown in the tune reports looks to be correct. If it is correct (weaker masses are seen in the spectrum), it is likely that the spectrometer is functioning properly.

If you are running SIM mode, the baseline may well be flat - or very close to it. This depends on the ions being used.

If you do not find the baseline problem to be a data acquisition setting, please post the conditions you are using for the chromatograph and mass spectrometer, this will help determine a likely cause for the problem.

[Peter Apps]

I am not familiar with the Shimadzu system, but you may find that there is a threshold setting for ion abundance, below which the software puts the signal to zero. This can easily give a perfectly flat baseline with peaks suddenly jumping out of it.

Peter

[Tony]

We had a similar problem some time ago with our Thermo GCQ. It turned out one of the cooling fans had failed, which led to periodic temperature-related shut-down of one of the power supply boards an a resulting sporadic "flat baseline" during sample runs. We were fooled for some time into thinking it was a sample issue, because the baseline went flat at a fixed time into every run - but it was just coincidental with the control-board power-up time after sample injection.

If you have a hardware problem (like ours was), the baseline issues should occur independently of the sample composition - i.e. your baseline problem should sometimes wipe out major peaks too. However, if you always see all your major peaks, and the space between them are flat baseline regions, it points to a thresholding problem as others have suggested.


thanks
Tony

[pimezon]

everyone, thank you for the suggestions. I will be testing out each of the leads put forth here. My first post here and I am glad I stumbled across this forum. cheers.

[DSP007]

Report on the results please. First ugly when the conversation ends in mid-sentence. Second of all may be similar problems
Third rejoice together your success.