No molecular ion peaks anymore - only doubly charged masses

Dear all,

I have recently encountered a problem with our LC-MS. We operate a Agilent 1260 Infinity with a G6125B LC/MSD. Our standard conditions are H2O/MeCN with 0.1% FA. Over the past few months, I noticed that for bigger compounds (>700 Da), I only saw "half masses" which corresponded to the doubly charged species - though I had run the same compounds before and received clear molecular ion peaks. Now, even more recently, this also happened to much smaller compounds (~300-500 Da) for which I previously got clear molecular ion peaks. I have even seen some triply charged species. For a lot of them, NO molecular ions are visible anymore. We have done some software updates etc. but the methods have remained the same. We have now had a play with the fragmentor and capillary voltage, however no change.

I would be grateful for any ideas what could be going wrong here. We have not changed any relevant MS settings in the past few weeks/months but it would be nice to have the molecular ion peaks show up again.

Many thanks in advance for your help!

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