Contamination peaks from ESI - cluster ions and PEG polymers

Cluster ions

+ve
(CF₃COOH)_n H⁺ cluster peaks 114 amu apart
(CF₃COONa)_n Na⁺ cluster peaks 136 amu apart
NOTE: you may see mixed clusters

-ve
(CF3COOH)nCF3COO- cluster peaks 114 amu apart
(CF3COONa)nCF3COO- cluster peaks 136 amu apart

PEG polymers

HO-(CH₂CH₂O)_n-H ethoxylate chains 44 amu apart