Sodium nitrate, 2% solution is a component of special staining kits, such as Grocott kit, stabilized, PASM/ Jones kit, stabilized, as well as Feulgen kit. Grocott kit and PASM/ Jones are used for visualizing argentaffin structures in histology. For diagnostic purposes it is most commonly used for impregnating basal membranes and fungi using silver. 1,2-glycols are oxidized to aldehydes by treating the section with periodic acid solution. During incubation in silver-methenamine-borate working solution aldehydes are reduced to primary alcohols with simultaneous reduction of silver ions to elementary silver (dark brown-black). Section toning follows using gold chloride solution that enhances target structures staining, as well as removes non-specific staining. Excessive unbound silver-gold bonds is removed by rinsing the section with sodium thiosulfate solution. Finally, the sections are exposed to Fast Green F.C.F. dye (Grocott kit, stabilized) or Nuclear Fast Red dye (PASM/ Jones kit, stabilized) that stains background structures green or red creating a clear and visually rich contrast to brown-black stained target structures.
Feulgen kit is used as cytochemical method of semiquantitative determining DNA in histology and cytology samples.