Same compound with odd behavior between 2 MS's

[dkotes]

The compound flies on the Micromass Q-TOF very well, but with the wrong mass (showing as +4 instead of +1). On a Micromass triple quad, it flies terribly, but it flies at the correct +1 m/z.

Does the Q-TOF need to be re-calibrated? Compound is around 900 m/z so it's pretty big, messing with cone voltage didn't seem to do anything. Wondering what ways we could optimize the tunes so it could either fly well on the triple quad, or give the correct mass on the Q-TOF.

Thanks

[lmh]

do other compounds come out at their expected masses in the Q-ToF?

[dkotes]

Yes we used an internal standard and that compound came out at the expected mass, but it had half the molecular weight. Wondering of the accuracy is starting to stray with higher molecular weight compounds.

[JMB]

It sounds like the mass calibration is very bad on the Q-Tof.

If you use a calibrant such as an aqueous soln. of CsI, peaks
at m/z 133 (VERY intense; do not scan across this without lowering multiplier !!), 393, 653, 913, 1173, 1433, etc. will be observed. Tune on the m/z 913 signal to optimize S/N and peak shape, and set scan range to say m/z 350-1475.

NB. m/z values are rounded.