The benzidine technique for histochemical detection of the SO4 ion

The benzidine technique for histochemical detection of the SO4 ion was studied analytically on filter paper strips loaded with 0.02 ml of solutions of sulfate containing and sulfate free substances. The influence of the benzidin solution pH on the SO4 and PO4 ion precipitation was analysed and the experimental condition where the SO4 ion was specifically precipitated was established. In basis on this study a benzidine histochemical technique suitable to detect the SO4 ion without interference of the PO4 ion was proposed for tissue sections. This technique has some advantages on the other benzidin techniques previously proposed mainly concerning its specificity.