HRMS

[syedsaeedali]

I started working on HRMS (JEOL- MS700) coupled with Agilent GC7890, though having experience on GC but MS is just a begining, when analyzing samples, in some cases only one peak appear grom GC, whichmake my Job easy to understand the molecular ion peak, and giving answer tor researcher.
but in most of the cases researcher submitting samples(natural product or synthetic chemistry), which elute multiple peaks, even the base line are not smooth,
and in some of case I can create the targeted m/z, but in some case targeted m/z can not be found,In this what could be the appropriate answer for the researcher to submit.

Need comment from expert of HRMS/GC


Regards

[tlahren]

You have many unknowns here. Does the researcher know the expected structure/MW? Are you running a SIM style method or full scan HR? What resolution is required to obtain qualitative assurance? Are you using an internal mass reference (FC43, PFK etc.)? With sector instruments it is absolutely crucial that the ion source be extremely clean and that the instrument is tuned properly. It took me almost a year to "get the hang" of tuning a sector instrument with reliability.

You also have to be sure that your compound of interest will elute using the proposed GC method. Usually I would have another GC/FID or GC/quadMS with a similar column for GC method development. Then use this method on your GC/HRMS system when you have a good RT on your suspected compound.

You are also relying on the fact that the researcher purified their compound well enough to get a GC response larger than background peaks (as it sounds this may be a problem for you).

In the past we used TOFMS with direct infusion (no LC or GC) and an internal mass reference to get accurate mass info for synthetic chemists. This way you do not need to worry about where it elutes in the chromatogram if you are only worried about a mass assignment for the compound. Does your system have capabilities for a DI probe which you could perform these tests with?

Just some suggestions and questions of mine.

Ty

[syedsaeedali]

Yes,,,Researcher knows expected Structure in most case and tentative Mol. Mass in all cases, normally using full scan,
usually runing on Kow resolution 1000 and high resolution 10,000. every time prior to use perform the Calibration using PFK.
and tuning also performed accurately, since instrument is almost new using since last 4 months, so hoping the cleanness of Ions source.
yes I am not sure about method I am just running and general method starting from 80 degree Celsius and created couple of ramps to end up at 280 degree Celsius, since column limit is not more than 300 degree Celsius.( need your more input in this).

Note, Between my last posting and this note, I got same scenario ( multiple peaks) so I used Direct probe method, and it works well, and got the given target m/z peaks, which I also verified by using CI ionization using direct probe.

By the way I am not very much familiar with SIM analysis. I can understand it is done for quantitative analysis, but in what scenario, I can use SIM? please advise me.

another note. What Kind of research I can be done on this machine, to publish the research papers.
please give me tips on it.
my email is., syedsaeedali@hotmail.com in case

[tlahren]

You are correct about SIM. It is mostly used to obtain better sensitivity for compounds where you know the mass and retention time. Probably not what you are needing.

To answer your other question about what kind of research can be done... It sounds like in your scenario you will most likely be using it for accurate mass validation of synthetic molecules. I believe you would only be a small section in the paper that the researcher writes on the synthesis of their compound. They will just say that the mass was validated on the HRMS (JEOL- MS700) and determined to be ###.#### amu at # ppm mass accuracy. It will be a key part of the paper but only a small fraction of it.

I use my sector instrument for low level quantitation of very high molecular weight compounds. They have very low GC response so we use the HRMS method in a SIM mode so we get very high sensitivity to our compounds. Although my research relies heavily on this instrument, when we write a paper it will only be a small blurb about the instrument and analytical conditions.

It sounds like you have a lot of the optional accessories for your instrument. I believe you will be able to use this machine for a lot of different research ventures. I think it will take you a while to find limitations to its uses. I don't know much about the Jeol instrument specifically, but with mine the limitations to me for future analysis would be limited mass range and scan speed. I have already reached the scan speed limitations for my applications. In some cases a HRTOF or QTOF might be better. However, the resolution power >60,000 on the sector instruments usually surpasses that of the TOFs. It is all application specific though.

I hope this helps a little more. I'm not sure what other information I can provide you, but feel free to ask more if you have any other questions.

Ty