Ion
mobility spectrometers (IMS) separate ions based on their ion
mobility, which depends mainly on collision cross-section, mass, and
charge of the ions. However, the performance is often hampered in
electrospray ionization (ESI) by the appearance of multiple ion mobility
peaks in the spectrum for the same analyte due to clustering and additional
sodium adducts. In this work, we investigate the influence of solvents
and buffer additives on the detected ion mobility peaks using ESI.
Additionally, we investigate the effects of an additional chemical
ionization (CI) induced by plasma ionization on the ions formed by
electrospray. For this purpose, we coupled our high-resolution IMS
with a resolving power of R
p = 100 to
a time-of-flight mass spectrometer. Depending on the analyte and the
chosen additives, the ionization process can be influenced during
the electrospray process. For the herbicide isoproturon, the addition
of 5 mM sodium acetate results in the formation of the sodium adduct
[M + Na]+, which is reflected in the ion mobility K
0 of 1.22 cm2/(V·s). In contrast,
the addition of 5 mM ammonium acetate yields the protonated species
[M + H]+ and a correspondingly higher K
0 of 1.29 cm2/(V·s). In some cases, as
with the herbicide pyrimethanil, the addition of sodium acetate can
completely suppress ionizations. By carefully choosing the solvent
additive for ESI-IMS or additional CI, the formation of different
ion mobility peaks can be observed. This can facilitate the assignment
of ions to ion mobility peaks using IMS as a compact, stand-alone
instrument, e.g., for on-site analysis.