NonImmunized_spleen_746_2

Negative ion mode IMS data were acquired with a 9.4T Bruker FT-ICR Solarix mass spectrometer (Bruker Daltonics, Billerica, MA, USA) equipped with a 2 kHz Nd: YAG (wavelength: 355nm) laser and an Infinity ion cyclotron resonance (ICR) cell. Laser power was optimized for each sample by adjusting in the range of 18-20%. Data were collected in negative ion mode from <i>m/z</i> 200-2,000 with a raster step of 30 µm and a data size of 1 MB per spectrum with a free induction decay (FID) length of 0.8389 s. Each pixel consisted of 500 laser shots with the minimum laser energy focus setting (~10 µm) at a frequency of 2000 Hz, and a smart walk of 25 µm was enabled to increase sensitivity. The mass-selecting quadrupole was set to <i>m/z</i> 350 and TOF of 0.8 ms. The resolving power of all imaging experiments was ~80,000 at <i>m/z</i> 766.54. External calibration was performed prior to analysis and internal lock-mass calibration was performed using <i>m/z</i> 885.5494 ([PI(18:0_20:4)-H]^-) during image acquisition.