6520a accurate mass q tof ms

To determine the purity and the mass of the peptides, LC–MS
data were acquired on an Agilent 6520 Q-TOF LC–MS system. Lyophilized
peptides were suspended in 0.1% formic acid in water to obtain a final
concentration of 1 mg/mL. Five microliter of the sample was loaded
on an Agilent Technologies 43 mm C18 Chip column. Agilent Technologies
1200 Series Quaternary high-performance liquid chromatograph was used.
LC gradient: initial conditions 3% B (A: 0.1% formic acid in water;
B: 99.9% acetonitrile, 0.1% formic acid), gradient to 80% B over 9
min, hold at 80% B for 3 min, ramp back to (0.5 min) and hold at (2.5
min) initial conditions. An Agilent Technologies 6520A Accurate Mass
Q-TOF MS with integrated Chip Cube source was used to collect data.
Data across a total of 15 min of elution were collected. MS data were
collected between 295 and 2500 m/z, and MS/MS data were collected between 70 and 2500 m/z at 2 spectra/s. Peptides with counts >2000
were picked for MS/MS.
LC–MS for the fibrils was obtained
using an LTQ Orbitrap XL mass spectrometer. Samples were precipitated
using ice-cold acetone. The pellet was recovered by centrifugation
(16 000g) and washed twice with 80% acetone
(in water). The pellet was dried and resuspended in 100 μL of
urea buffer (6 M urea, 2 M thiourea, 0.1 M ammonium bicarbonate).
No particulates were observed, suggesting fibrils were completely
dissolved in the buffer.