Qualifier Ion Issue

GILAB,

When changes are made to a GCMS system (Maintenance, Source Cleaning, etc) the fragmentation of analytes can change significantly.  This is usually minimized by "tuning" the instrument.  The problem lies in how the instrument is tuned and whether you utilize automated tuning procedures or not.  I do not know which make or model of GCMS you are using but my suggestion is to compare the tunie results before the maintenance and afterwards.  I would be willing to bet there are differences.  You may need to adjust the final outcome of any automated tuning procedures to refine them to have more consistent results.

If you can reply with the make/model of GCMS as well as which tuning procedure you are using I may be able to offer more insight.

Dan

Thanks very much Dan,

We have an Agilent GC/MS.  The GC model number is 6890N G1530N, and the MS is 5975 G3171A. 

Here’s some more info that I hope is helpful.  Our pre- and post-maintenance Autotune reports are relatively similar, with EM volts slightly decreased from 1300 to ~1100.  Also, the relative abundance of ions 69, 219, and 502 have stayed around 100%, 70%, and 6%, respectively.  These abundances are ~425k, 290k, and 25k, respectively.  There doesn’t seem to be any major changes in our tune reports from before and after maintenance, with the EM value being the largest change.

There are some situatuions where this can happen due to co-eluting analytes with common ions.  Typically this only happens in complex analyses though.  Are there any closely eluting analytes in your analysis?  What components are we dealing with?

Dan

Here’s a picture of our TIC Chromatogram: https://drive.google.com/file/d/0B5ELMIp-sCMhMG8xYTRhRUFfOFhBLVd1dE5URjc1Rkw2MW1Z/view?usp=sharing

We are measuring standard solutions of sterols.  Most are having this Q-ion issue, including compounds like “m” and “n” which are not co-eluting with anything else.  Also, we haven’t seen any kind of pattern in the Q-ion relative abundances whenever we ran serial dilutions of standards. 

If you would like to contact me directly and send me the datafiles to look at I can try to determine what is going on.  My email is on my website.

Dan