The synthetic dyes in tested sample

The synthetic dyes in tested samples were screened by comparing the multi-wavelength chromatographic fingerprints of normal unadulterated chilli samples (chilli powder samples was selected) and the tested samples. A newly emerged peak, which was not seen in the chromatographic fingerprints of normal unadulterated samples, was regarded as possible existence of synthetic dyes in tested samples. A peak in the tested samples was regarded as newly emerged peak when retention time of the peak did not match that of the chromatographic fingerprinting peaks of normal unadulterated samples. Generally, For the analyte identification by HPLC–DAD, the analyte shall elute at the retention time that is typical for the corresponding calibration standard under the same experimental conditions. The retention time of the analyte shall be the same as that of the calibration standard at a tolerance of ±2.5% for LC (European Commission, 2002). A retention time tolerance of ±2.5% was used for the identification of a newly emerged peak (suspected dye peak). The suspected dye peaks were identified using common known synthetic dyes standard on the basis of same retention time and the spectral characteristics. The peaks that could not be identified with known dyes standards were further identified through sample purification, liquid chromatography-tandem or high-resolution mass spectrometry analysis, etc.