Metabolomic Profiling by CPSI-MS
A full description of the CPSI-MS instrumentation can be found in a
prior publication.21,22 After the serum was thaw under
ambient conditions, 3 μL serum and 1 μL 4-chlorophenylanine (internal
standard, IS) were transferred onto the tip of a conductive polymer to
form a dried serum spot for data acquisition. Upon addition of
methanol-water (7:3, v/v, 3 μL) onto the dried serum spot for
metabolites extraction, high voltage (+4.5 kV) was applied to the
conductive polymer tip to trigger the spray ionization process. Data
were recorded in the Department of Chemistry, Fudan University using an
LTQ Orbitrap Velos mass spectrometer (Thermo Scientific, San Jose, CA,
US.). The full scan range was set at m/z 50-1000 under positive
mode. The data acquisition period for each sample lasts for 15 seconds.
The intensity of each metabolite ion was normalized with the IS
intensity of each sample ([M+Na]+, m/z222.0292). Quality control (QC) samples were prepared by pooling equal
volumes of 20 HC and 20 OSCC serum samples. QC samples were analyzed
throughout the run to monitor the CPSI-MS system variation. OSCC and HC
serum samples were run in alteration with the QC samples evenly inserted
into the entire sequence every 30 samples.