Comprehensive impurity profiling and quantification of Sudan III dyes by gas chromatography/mass spectrometry

• Comprehensive GC/MS method was first proposed for impurity profiling of Sudan III dyes.
• A total of 24 impurities including 5 coplanar impurities were first time identified by GC/MS.
• TMS derivatization provided excellent sensitivity and selectivity for polar impurity profiling.
• The formation pathways of impurities during the manufacture of Sudan III were suggested.

A novel analysis strategy was created for comprehensive qualitative and quantitative impurity profiling of the coloring agent Sudan III by gas chromatography/mass spectrometry (GC/MS). The identification of impurities in commercial Sudan III was performed by GC/MS combined with trimethylsilylation (TMS). A total of 24 impurities were identified or tentatively characterized in commercial Sudan III dyes by GC/MS and were mainly classified as phenylazo and naphtholazo analogs. Four new impurities with coplanar structures, suspected of being toxic compounds, were observed in commercial Sudan III dyes. For further identification and sensitive detection of polar impurities, an extract was trimethylsilyl-derivatized to improve the GC chromatographic properties and mass spectrometric detection sensitivity. On the basis of the impurities identified by GC/MS, pathways for the formation of the major impurities during the manufacture of Sudan III were suggested. Four impurities regulated by the EU commission and the US Code of Federal Regulations (CFR) in Sudan III were quantified by GC/MS-scan mode. Method validation was conducted to determine linearity, precision, accuracy, and limit of quantification (LOQ). The linear dynamic range extended from 0.001 to 4.0%, with a correlation coefficient (R2) greater than 0.997 for GC/MS. The LOQs of the impurities ranged from 2.73 to 4.39 μg/g for GC/MS. Based on the established method, the levels of regulated impurities in five commercial Sudan III dyes manufactured by different chemical companies were successfully determined. This study provides very useful information for the quality control of Sudan III and evaluation of its manufacture.