Molecular ion identification

[shelleyj]

Hi,
I'm new to using Turbomass for GC-MS (Perkin Elmer Clarus). I have two questions:

1) For the MS method, I had it scanning from 50-600, which was resulting in not very good library matches on the low MW end. A colleague suggested that I make the scan range a little smaller, and lower, so I changed it to 40-400 amu. This has resulted in higher quality matches, but now, for instance, I have a peak of interest at 4.5 min which was previously identified as mass 55. Turbomass reports the retention time and the molecular ion on the chromatogram. With the new search parameters, it is identifying the same peak (same RT and shape) as having a molecular ion mass of 44. Does this mean the previous samples run with the 50-600 amu scan range are probably misidentified?

2) Toward the end of the chromatogram (>25 min) as the oven temp rises (60-300C, 7C/min) there are a lot of small peaks that all identify with ion 73.21 and are spaced very regularly. Is this column bleed?

Thank you!

[Don_Hilton]

The compunds identified in the chromatogram with a mass range of 50-600 may or may not be correctly identified. You need to examine the spectra and see if they make sense - I just made a post under the data systems section. , answerign a question on how people use GC/MS data. See if any of that helps.

Regularly spaced peaks with a significant m/z 73 ion are likely to be silanes.