Determination of Organic Impurities and Subsidiary Colors in Ext. D&C Violet No. 2 (Acid Violet 43) by...

The U.S. Food and Drug Administration (FDA) batch certifies the anthraquinone color additive Ext. D&C Violet No. 2 (XV2, "Ext." stands for "External") to ensure that it meets requirements published in the Code of Federal Regulations (CFR). XV2 is manufactured by condensing 1,4-dihydroxy-9,10-anthracenedione (DHAQ) with p-toluidine (pT) followed by sulfonation of the condensation product at the ortho position of the pT group. Organic impurities include residual intermediates, DHAQ and pT, and reaction byproducts, 1-hydroxy-9,10-anthracenedione (MHAQ) and p-toluidine-m-sulfonic acid (PTMS). Sulfonation of the condensation product at the meta position produces an isomeric subsidiary color (mXV2). Other subsidiary colors include a dye which is itself certifiable as D&C Green No. 5 (G5) and a sulfonated phthaloylcarbazole (AV43C).

This paper describes a simple and sensitive UHPLC method for the determination of CFR-specified organic impurities in XV2 samples submitted to the FDA for batch certification.

The UHPLC method uses a 1.7 mm particle size C-18 column with aqueous ammonium acetate and acetonitrile as eluants and photodiode array detection at two wavelengths. Analytes are identified by comparing their retention times and ultraviolet-visible spectra to those of reference standards.

Method validation demonstrates linearity, limits of detection, limits of quantitation, accuracy, and precision. Excellent regression coefficients for the calibration curves were obtained, with values >0.999. Overall accuracy was 98.2-104.3% and precision was 0.0075-5.27% for all analytes.

The UHPLC method satisfies the accuracy and precision requisites for routine certification.

The UHPLC method reported here can be used for the determination of CFR-specified organic impurities including intermediate starting materials, reaction byproducts, and subsidiary colors in samples of XV2 submitted to the FDA for batch certification. The method's LOD is well below the CFR specification levels.