Description General description o-Tolidine is widely used in the aniline dye industry for the synthesis of different azo dyes. Application o-Tolidine (3,3′-dimethylbenzidine) may be used as an analytical reference standard for the determination of the analyte formed from azo colorants in toy products by high-performance liquid chromatography with UV detection. Refer to the product′s Certificate of Analysis for more information on a suitable instrument technique. Contact Technical Service for further support. Sensitive colorimetric reagent for gold and for free chlorine in water. Warning May be carcinogenic.