[Shrsh]

When using the "compound optimization" method to establish an MRM method for a compound with a molecular weight of 162 g/mol, the equipment detected ion transitions of 163.0 -> 84.5 and 163.0 -> 56.8. However, when running with these transitions, it appears they are originating from our solvent, DMSO, commonly used in our analyses. DMSO has a molecular weight of 78.13 g/mol and does not typically produce fragments of 84.5 or 56.8. We have used DMSO in other experiments without any issues until now.

We suspect this may be an equipment problem and would appreciate assistance in troubleshooting this issue.

[rjb]

Hi Shrsh,

What makes you suspect that it's the DMSO giving rise to these ions rather than the analyte?
Unless something has gone very wrong (perhaps worth running at least a check-tune to make sure), there is no way DMSO or it's constituent fragments could possibly even pass your first quad (I presume its a QqQ instrument), let alone the collision cell and third quad and then somehow reach the detector!

I am intrigued and would love to know more.

R

[Shrsh]

Thank you for your reply!

Would there be something wrong with DMSO?
The DMSO we were using is HPLC grade (see attached), but we usually only have <0.1% when mixing the samples.

[rjb]

Hi,

I'm still a bit confused as to why you think you're detecting DMSO rather than your analyte? Am I right in  guessing that your blanks (which contain DMSO but no analyte) are giving results? If so, then I would imagine that somebody has most likely has managed to contaminate your DMSO with analyte! There are alternative possibilities, but DMSO contamination is most likely. 

Probably worth swapping your DMSO for fresh. Bear in mind that MS is a lot more sensitive to poor solvents than UV or DAD, and wherever possible, it is best to use LC-MS grade, at least for the run solvents. Not critical for what you're using your DMSO for, but worth bearing in mind. I tend to use LC-MS grade solvents for everything, even GC-MS!

R

[Shrsh]

Yes ---- We found this issue in our background check, which is 0.1% DMSO, PBS + IS. Only PBS + IS background shows no suspected peaks. We further increased DMSO conc., and the peak intensity increased proportionally.

We have ordered MS grade DMSO for replacement ---- Thank you! We are an enzyme kinetics lab, and most of the organic solvents are not able to be used due to they are toxic to the enzyme. DMSO is less toxic to the enzyme compared with other organic solvents, it is kind of unavoidable in our experiments.