What kinds of adducts are commonly observed in ES–MS?

For Electrospray MS in the positive mode, it is typical to detect (M+H)+ and relevant fragment ions, whilst with the negative ion mode, (M-H)+ molecular ions are normally observed. It is also common to observe clusters and other adduct ions as well. Molecules tend to cluster when run by electrospray, particularly if the sample concentration is high. Larger molecules that readily take on multiple charges, such as proteins and oligonucleotides, commonly appears as multiple groups of ions with increasing charge