Chromatography Forum

The mass chromatographic for m/z 128 in the Before data shows fronting, indicating the compound is fairly polar. This would be the case if this peak primary represent furaneol, which has an OH group. If the furaneol is oxidize to the corresponding saturated dione, the analyte will give a sharper more symmetrical chromatographic peak. When I create a spectrum in the NIST MS Search Program using the data displayed by Ram, I associated this 2,5-dimthylfuran-3,4- dione with it. The NIST MS Search Program calculated a RI value of 1053 for this compound. The calculated RI value for furaneol was 1022. Most of the RI values taken from the literature for furaneol (in the NIST RI database) were on this order.

I agree that the RTIC chromatographic peak of m/z 128 in the Before display at 11.53 min. probably represents two compounds; furaneol and something with a molecular weight of 140 Da; however, it appears that there is a lot of this m/z 140 compound represented by that chromatographic peak; therefore, I would like to eximine the mass spectrum representing the apex of this chromatographic peak, before I commit. The mass chromatographic peak of m/z 128 at 12.04 min in the Now sample could represent an oxidation product of furanol which has two carbonyl groups and no double bond.

If you can get an authentic sample of furaneol, chromatographic it and see if you can oxidize it. See if the retention time and mass spectrum of the oxidize product match your results. It is possible that the furaneol is oxidized (or metabolized) by the fruit over time after the fruit is picked. Try repeating the analysis on freshly picked fruit.

Thanks David for the info! Do you want me to post spectra from apex of the corresponding peak from both 'before' and 'now' TIC?

Thanks zokitano and Don for the comment on use of glass wool for SPME.
In which other cases of extraction, 'dis-use' of glass wool applies? eg...
for direct solvent extracts of fruits...must be used
for solvent extracts of aqueous distillate...may not be used (is that true?)
and for SPME .......must NOT be used..

My habit is to use glass wool for anything injected as a liquid unless I am trying to do quanntitation at trace levels. I may skip the glass wool in that case to avoid activity and to improve limits of detection. I also tend to run my inlet a bit cooler than the maximum temperature of the GC program to keep compounds that will not elute from the column in the inlet and to avoid breaking down heat sensitive compunds. This may require more frequent changes of liners, but helps to keep nonvolatile junk off the column - extending column life.

Glass wool also catches septum crumbs - and a change of liner gets rid of the silane peaks bleeding off the crumbs.

Ram,

Post the spectrum that has a suspected molecular ion peak at m/z 128 and whose mass chromatographic peak has a retention time of 12.04 min.

If posible, e-mail me the two data files.

Ram,

Post the spectrum that has a suspected molecular ion peak at m/z 128 and whose mass chromatographic peak has a retention time of 12.04 min.

If posible, e-mail me the two data files.

Hi,
I have already posted the spectra of 12.04 RT (Wed Jan 28, 2009 9:25 pm),
I didn't get, which other one do you want me to post..

Ram,

I still don’t have an answer for you . Looking at the spectrum represented by the apex of the m/z 128 mass chromatographic peak, it is reasonable to believe that the mass spectral peak at m/z 128 is a molecular ion peak. The peak at m/z 110 could represent an odd-electron (OE) fragment ion formed by the loss of a molecule of water from the molecular ion. The peak at m/z 95 could represent an even-electron (EE) fragment ion formed by the loss of a methyl radical from the M - H2O ion. The peak at m/z 95 probably does not represent an ion formed by the fragmentation of a molecular ion because a loss of 33 is not a logical loss.

There are two other OE fragment ion peaks at m/z 84 and m/z 58. The intensities of these peaks are not insignificant. The peak at m/z 58 usually represents a H2C(COH)CH3 OE ion. When two OE fragment ion peaks are observed in the spectrum and one is at m/z 58, that ion is usually formed by the fragmentation of the higher m/z value OE ion, which would be at m/z 84 in this spectrum. This means that the neutral loss form the ion with m/z 84 to form the ion with m/z 58 would have to be 26, which can only be a molecule of acetylene. It is possible that these two OE fragment ions are not related.

The ions represented by the mass spectral peaks at m/z 43, 71, and 85 are probably not aliphatic ions.

It is still possible that this mass chromatographic peak represents more than a single compound. It might be a good idea to look at this area of the RTIC chromatogram in AMDIS. If the data were acquired and stored in profile mode, you might be able to use MassWorks from Cero Biosciences to assign accurate values to the various mass spectral peaks so that you can determine their elemental compositions.

Problem solved!
We used to filter the extract through glass wool to remove suspending particles during extraction. We just replaced this step by centrifugation and now there is a clear big peak of furaneol.