Additional Supporting Information may be found in the online version of this article.

AR_21103_sm_suppinfofig1.tif2175KSupporting Figure S1: Comparison of tissue morphology from frozen and acid/ethanol fixed tissue. Optical images of acid/ethanol fixed (Left panel) and frozen (Right panel) chick heart sections. Fine tissue structures are apparent in the fixed tissue section, but absent in the frozen tissue section. Note that upper left portion of extracardiac tissue was removed during dissection of fixed tissue sample.
AR_21103_sm_suppinfofig2.tif16664KSupporting Figure S2: Comparison of spectra from frozen and acid/ethanol fixed tissue. (A) Example spectrum from a chick heart section collected from frozen tissue, washed with ethanol and spotted with DHB matrix. (B) A higher number of spectral features, particularly in the low mass range, and increased total ion current are evident in an example spectrum from an acid fixed/paraffin embedded chick heart tissue section prepared with DHB matrix. Although ethanol washes could remove hydrophilic proteins from frozen sections, this step is commonly used to produce optimum matrix crystallization and the highest quality images from frozen tissue. Both spectra are plotted on the same absolute intensity scale.

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