The chemical nature of de Tomasi Schiff reagent. Changes of certain physical-chemical and histochemical properties during ageing.

Samples of de Tomasi's Schiff reagent were allowed to age. During this process physical, chemical and staining properties of the reagent were monitored. Certain physical and chemical properties of Schiff's reagent correlated with staining intensities. Thus a fall in the iodine titre and a rise in the pH (indicating loss of sulphur dioxide) accompanied falls of intensity of Feulgen-stained frog red-cell nuclei and of P.A.S.-stained cellulose sheet. Ageing sulphite solutions exhibited analogous physical and chemical changes. Thin layer and ion-exchange chromatography of Schiff's reagent demonstrated at lest four colourless (but colour generating) derivatives, all of which were cationic. NMR spectroscopy showed that the carbon skeletons of these compounds were simple and symmetrical. The ageing of Schiff's reagent appears to be primarily due to changes in its inorganic components. The aldehyde-reactive compounds probably differ only in the nature of the oxysulphur substituent on their central carbon atom.