|Title||»||Small molecules: need negative ion capability|
One thing that caught my eye is the current setting of everything to positive charge (ESI+). I tried to set a precursor to charge of -1 in the import/transition list table, thinking it would be all too simple if that was the ‘trigger’ for an ESI- method. I can’t remember if we have talked about this before or not, but the main thing Skyline would need to do is to simply annotate an ion as negatively charged, adjust the M-H calculation accordingly, and set the mass spectrometer mode to ESI- in the method file for those particular analytes. Waters and many other TQ instruments allow ESI+ and ESI- ions in the same method, thus performing ‘polarity switching’ as part of the SRM method.
We are building methods right now for fatty acids (Omega 3 and Omega 6) and downstream metabolites, so that is why ESI- just happens to be high on my list right now.
J. Will Thompson, Ph.D.