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Note: This experiment was performed as part of a teaching lab experiment which has concluded, so I would not be able to alter any experimental conditions. I was also unable to modify any of the variables used in the GC-MS experiment itself, but I may be able to provide these upon request.

I would like help in the interpretation of this spectrum from experienced chromatographers, I expect more information to be required other than the spectra provided, but due to my inexperience I am uncertain what they might be. Please do point them out in the comments if necessary.

This is a spectrogram plot performed in Mathematica of the relevant data for octanol quantification (octanol normally elutes at approximately 5.8-5.9 minutes, and did so in the positive control samples.)

The GC-MS machine was not used by any other group during the 2 days, and the only samples run on it during the 2 days were either ddH2O (with or without octanol) or sterile filtered cultures of E. coli in M9 growth media+glucose (with or without octanol).

All images are thumbnailed, click on the link to open a full resolution image.

Representative samples taken on Wednesday, consistent high levels of tailing. All samples are in ddH2O.

ddH2O enter image description here 25mg/L octanol enter image description here 100mg/L octanol enter image description here

Samples taken on Friday, varying amount of tailing

ddH2O enter image description here Blank growth media enter image description here

100mg/L octanol in ddH2O, not tailed enter image description here

50mg/L octanol spiked into growth media enter image description here 100mg/L octanol in ddH2O, tailed enter image description here

The noise present (at m/z 59 and 78) seemed inconsistent with the column (100% DMPS) nor any of the alternatives present on a list of possible column bleed spectra.

Octanol's solubility seems to be 2300mg/L as seen here, and I don't find it very likely that the low solubility of octanol in ddH2O resulted in the tailing.

What could have caused the noise at m/z 59 and 78, and why was the tailing so different despite near-identical experimental conditions?

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