Determination of 1,3-diphenyltriazene and azobenzene in D&C Red No. 33 by solvent extraction and reversed-phase high-performance liquid chromatography.

Data are presented for the determination of trace levels of 1,3-diphenyltriazene (DPT) and azobenzene (AB) in D&C Red No. 33. The contaminants are extracted with chloroform from an aqueous solution of the color, and the chloroform is removed under vacuum. The residue is dissolved in acetonitrile and the solution is analyzed by reversed-phase high-performance liquid chromatography (HPLC) with detection at 365 nm. DPT and AB were determined at levels of less than or equal to 439 ppb and less than or equal to 2.2 ppm, respectively, in samples of commercial D&C Red No. 33. Method precision for the DPT determination (five analyses) was 6.8% relative standard deviation. The UV-Vis spectra of the HPLC analytes, obtained by using a rapid-scan diode-array spectrophotometer, were used to confirm the identity of the DPT and AB responses produced during analysis of the D&C Red No. 33 extracts. The method is also useful for the separation of cis- and trans-AB.