9.4 t apex ultra hybrid qh fticr ms

Extracted FFAs were analyzed using a 9.4 T Apex-ultra™ hybrid Qh-FTICR MS (Bruker Daltonics, Billerica, MA, USA) equipped with a NanoMate system (Advion BioSciences, Ithaca, NY, USA) in the negative ion mode. 0.1 µL of the sample followed by 0.5 µL of air was introduced directly into the nanoESI source, with a voltage of -1.8 kV and a head pressure of 0.7 psi at a flow rate of 100 nL/min. Each spectrum was accumulated 10 full scans over the mass range of 150-400 Da and the resolution was 200,000 at m/z 400. A mixture of C_15:0 (molecular weight = 242.22458 Da), C_17:0 (270.25588 Da), and C_21:0 (326.31848 Da) was employed to calibrate the instrument before analysis.
Serum unsaturated FFAs in this study were identified on the basis of their observed accurate molecular masses and reliable isotope distributions detected by FTICR MS. Their mass error was ≤ 0.00025 Da and the relative intensity error of their isotopic peaks was < 2%. For the missing levels of unsaturated FFAs, the baseline intensity in each spectrum was adopted for the following statistical analysis.

All experiments were performed by a 9.4 T Apex-ultra™ hybrid Qh-FTICR MS (Bruker Daltonics, Billerica, MA, USA) equipped with a NanoMate system (Advion BioSciences). The NanoMate system includes a cooling unit set at 4 °C to cool sample solutions and nanoelectrospray source, which includes a 96-well plate, conductive pipette tips, and nanoChip with a 20 × 20 array of nozzle. The sample volume of 0.1 µL was directly infused using a low delivery gas pressure of 0.7 psi, and a voltage of -1.8 kV was applied to the nozzle to generate nanoelectrospray at a flow rate of approximately 100 nL/min.
A mass spectrum was accumulated by 10 full scans over the m/z range of 150-400 with the resolution of 200,000 at m/z 400. A mixture of C_15:0 (molecular weight, 242.22458 Da), C_17:0 (270.25588 Da), and C_21:0 (326.31848 Da) was used to calibrate the instrument. All mass spectra were processed using DataAnalysis 4.0 (Bruker Daltonics). The FFAs were identified based on their observed accurate molecular masses relative to theoretical values with the mass error of ≤ 0.00029 Da and reliable isotope distribution relative to theoretical distribution with relative standard deviation (RSD) of <2%. The baseline intensity in each spectrum was adopted as their intensities of missing FFAs.