Safranine

SAFRANINE (sometimes Schfranik), coloring substances belonging to the group of azo dyes of a basic nature, usually in the form of hydrochloride salts. The simplest formula is phenol-S, while the more complex composition is toluidine-S, containing methyl groups. Commercial grades of S.: T, extra G, FF extra № 0, are mixtures of phenol- and toluidine-S. They appear as a brown-red powder, easily soluble in alcohol, less soluble in water (0.6%); the solution is red in color with yellowish-red fluorescence, unchanged by NH₃, and turns blue-violet with HCl. In microscopic technique, S. was introduced in 1881 (Hermann, Flemming, Pfitzner) for staining nuclei and mainly karyokinesis and since then has found wide application. It is used in an alcoholic solution diluted half with water, and in a saturated aqueous solution; it is better to use a saturated solution in aniline water (Babes). The preparation is left overnight or stained for several minutes with heating; after staining, differentiation in weak alcoholic acid (0.5-1% HCl) or better in a weak alcoholic solution of an acid dye (picric acid, light green, picro-indigo-carmine) is necessary, while at the same time additional staining occurs; only nuclei and karyokinetic figures should be stained red; sometimes S. also stains mucus. S. is often used in combination with hematoxylin (Rabl) either simultaneously or sequentially; together with gentian and orange, S. is part of Flemming's triple staining, which reveals achromatic figures and centrosomes. S. is a component of MinerVI-ni's stain for elastic fibers (so-called safranelin), which is a modification of Weigert's stain (the fuchsin in the latter is replaced by S. in MinerVI-ni's stain). Recently, a basic S. precipitating from solution under the action of KOH has been recommended for staining.