Identification and determination of 34 water-soluble synthetic dyes in foodstuff by high performance liquid chromatography-diode array detection-ion trap time-of-flight tandem mass spectrometry

An accurate method combining high performance liquid chromatography (HPLC) with diode array detection (DAD) and ion-trap time-of-flight mass spectrometry (IT-TOF/MS) was developed for simultaneous identification and quantification of 34 water-soluble synthetic dyes in foodstuff. Fragmentation patterns of synthetic dyes were proposed based on IT-TOF/MS. The molecular ion [M+H]+ was not observed in the conventional single-stage mass spectra for most of synthetic dyes. The single-stage mass spectra of synthetic dyes all afforded the diagnostic ions [(M-nNa+nH)+H]+ or [(M-nNa+nH)-H]− in the positive or negative mode. Doubly charged ions were the characteristic ions of azo dyes. An HPLC-DAD method was developed to analyze 34 synthetic dyes in foodstuffs. The limits of detection (LOD) for the dyes were 0.01-0.05 μg/mL. The recoveries were between 76.1% and 105.0% with a RSD ranging from 1.4% to 6.4%. This method was successfully applied to analyzing the 34 water-soluble synthetic dyes in 21 commercial foods.