Ubiquitin from bovine erythrocytes

Ubiquitin from bovine erythrocytes
(≥98% purity) and ammonium acetate were purchased from Sigma
Chemical Co. (St. Louis, MO, USA). Acetic acid and HPLC-grade water
were obtained from Fisher Scientific (Leics, UK). All reagents were
used without further purification. Two 10 μM solutions were
prepared by dissolving ubiquitin in either aqueous 1% Acetic acid
or in 100 mM ammonium acetate aqueous solution, corresponding to the
partially unfolded (charge states 7+ and 8+) and the native protein
conformations (charge states 5+ and 6+), respectively. Papaverine
hydrocloride (99%) was purchased from ACROS Organics and a 0.1 mM
stock solution was prepared in ACN/H₂O/AcOH 90:10:0.1 (v/v/v).
A series of dilutions were performed to final concentrations of 0.003,
0.03, 0.15, and 0.3 μM in order to map the stability diagram
of the Omnitrap under different space charge loads. Bradykinin acetate
salt (≥98%) was purchased from Sigma-Aldrich, and 1.2 μM
solution was prepared in H₂O/MeOH/AcOH 60:39:1 (v/v/v)
in order to measure the secular frequency of the ions under variable
space charge loads and across a wide range of excitation amplitudes.
Oxidized insulin chain B from bovine pancreas (≥80%) and myoglobin
from equine heart were purchased from Sigma-Aldrich. Insulin chain
B 10 μM solution was prepared in ACN/H₂O/AcOH 50:49.9:0.1
(v/v/v) and 10 μM myoglobin solution was prepared in H₂O/MeOH/AcOH 49:49:2 (v/v/v).