Fig. 3.

Representative combined mass spectrum detected by MALDI-MSI from an MDA-MB-231-HRE-tdTomato breast tumor xenograft. In the low-mass range, we detected phosphate-containing ions at m/z 125.0, m/z 146.9, and m/z 162.9, the phosphocholine head group at m/z 184.0 and a related ion at m/z 198.0, matrix-related ions at m/z 172.0, m/z 190.0, and m/z 379.0, as well as the fiducial marker cresyl violet at m/z 262.0. Stearoylcarnitine was observed at m/z 428.3, and lysolipids were detected in the mass range from m/z 450 to m/z 550. The heme ion was present at m/z 616.1. Abundant intact phospholipid molecular ions were observed in the mass range from m/z 700 to m/z 860.