Chromatography Forum

Hello everybody!
My question is that the compound's m/z is always [M+H] (in positive ion mode) or [M-H] (in negative mode)by using APCI source , is it right?
thanks of all

Not always the case but it is a good generalization.

For ms to "work" the compound must have a charge. Either through addition or removal of a proton, or by some other means. quaternary ammonium salts are a good example there are others.

You can inject NaI in water and see signal for iodine in negative mode. This is not due to addition or removal of a proton.