The aging of Gomori's aldehyde-fuchsin: the nature of the chemical changes and the chemical structures of the coloured components.

The chemical nature of Gomori's aldehyde-fuchsin (GAF) prepared by the method of Mowry et al. (1980) was studied by monitoring the staining characteristics and various chemical properties of ripening GAF solutions. Hydrophilic-hydrophobic characteristics were assessed by reverse-phase thin-layer chromatography; overall molecular sizes, and also the sizes of the conjugated systems, were investigated using hydrophobic gel-filtration. Other properties monitored included the nuclear magnetic resonance and visible spectra, the apparent pH, and the amount of precipitation. It was concluded that for GAF prepared by the Mowry et al. procedure: i. The purple, strongly staining components arising in the first few days of aging are Schiff bases derived from Pararosanilin. ii. These Schiff bases are slowly transformed into a variety of N-ethylated derivatives, which are weakly or non-staining. In addition to these chemical transformations, the quality of staining was markedly influenced by the tendency of GAF to precipitate; as much as three quarters of the dye was sometimes lost in this way during the first few days or weeks.