Negative Mode Check Sample?

[mburleson]

Hello,

If you've seen any of my previous posts regarding our Thermo TSQ Quantum Ultra, I have finally resurrected it after a year and a month! We have some chemists interested in using negative mode, and I have only had success with negative mode once and that was when I was in industry (circa 2016 - 2018). I'm curious if there's a good sample someone could recommend to make and keep on hand to check the mass calibration and S/N? I've seen papers testing sucrose and that would be easy. I have no method parameters yet, but know that I want a high sheath gas flow.

Also, has anyone encountered issues with the beam stability in negative mode on these Thermo MSDs?

[mathieu_stability]

The Thermo TSQ is a reliable instrument that delivers results.
As a technique, any LCMS will require optimisation of ionisation parameters in terms of gas flow, gas temperatures and voltage.
I would start with the LTQ negative ion tuning mix to calibrate the mass axis.
Then consider acid red or chloramphenicol for parameter optimisation.
Sucrose is also a posiibility as you noted for higher masses.
My other LCMS favorite in negative ion mode are the chlorinated phenols in the TCP antiseptic.

[mburleson]

The Thermo TSQ is a reliable instrument that delivers results.
As a technique, any LCMS will require optimisation of ionisation parameters in terms of gas flow, gas temperatures and voltage.
I would start with the LTQ negative ion tuning mix to calibrate the mass axis.
Then consider acid red or chloramphenicol for parameter optimisation.
Sucrose is also a posiibility as you noted for higher masses.
My other LCMS favorite in negative ion mode are the chlorinated phenols in the TCP antiseptic.

Thanks so much!

[mathieu_stability]

As I recall, the negative ions from the polytyrosine TSQ solution should be:
m/z 180.02 , 506.20 & 995.40