Figure 2. Normalization of PTX signal by internal standard spray approach.

Upper panels: untreated tumor and liver sections. Lower panels: tumor and liver sections from a mouse treated with PTX 60 mg/kg i.v. The images of PTX and sprayed d5-PTX ion signal are shown. The third images result from the ratio of the first two images. This normalization approach ensures that the irregular drug distribution seen in the first column is real and not caused by different ion suppression effect in different parts of the tumor. The homogeneous distribution observed in liver, instead, is confirmed by normalization.