Rapid Screening of 8 Dyes Illegally Added in Food by Direct Analysis in Real Time-High Resolution Mass Spectrometry

Industrial dyes are bright in color, low in price, and easy to obtain. They are easy to be added to food by illegal traders for quick profit. Most of these substances have carcinogenic, teratogenic and other effects, which are harmful for human health. The rapid screening and identification of illegally added dyes in food will help to fight against such crimes. In this study, a method of direct analysis in real time (DART)-quadrupole-electrostatic field orbital ion trap high resolution mass spectrometry (Q-Orbitrap HRMS) was established to rapidly screen eight industrial dyes, including alkaline orange 2, alkaline orange 21, alkaline orange 22, alkaline yellow 2, alkaline fuchsin, malachite green, rhodamine B and rhodamine 6G. Three kinds of swabs, carbon fiber, cotton and epoxy resin were tested for sampling, and carbon fiber was selected for its higher concentration effect and lower background interference. A bunch of carbon fiber bundle (1 cm, 6 000 pieces) wetted with 20 μL acetonitrile was used to wipe the sample surface, then the swab was analyzed directly by DART-HRMS. The ion source temperature of DART was optimized according to different targets. The positive ion mode was selected for HRMS. The target compound was firstly selected by the accurate m/z value in full scan mode, and then was confirmed by the two characteristic product ions. The mass errors for the eight industrial dyes were less than 3×10^-6, and the limits of detection were in the range of 0.01-0.5 mg/L. The repeatability error (RSD) was no more than 22%. The method was applied to detect alkaline orange 2 in yellow croaker samples suspected of adding industrial dyes. The qualification results were compared with the results acquired by a national standard method, and DART-HRMS was proved to have the advantages of simple pretreatment, fast analysis and accurate qualitative result. Additionally, different sampling positions on spiked yellow croaker were investigated. It turned out that gill, abdominal fin and abdomen were three parts where dyes were easily deposited, thus these were most efficient parts for swab sampling from the outside of yellow croaker. This method can provide a reference for the rapid screening of illegally added dyes in food.