Simultaneous qualitative and quantitative determination of 104 fat-soluble synthetic dyes in foods using disperse solid-phase extraction and UHPLC-Q-Orbitrap HRMS analysis.

Public exposure to synthetic dyes through foods has attracted ongoing and serious attention. Here we developed and validated a simultaneous screening and quantitation method for the analysis of fat-soluble synthetic dyes that most frequently found in foods, using C18 d-SPE clean-up and UHPLC-Q-Orbitrap HRMS on Full-MS/dd-MS2 mode. During a single run, 104 dyes including 6 pairs of isomers were distinguished based on chromatographic separation and unique product ions. The method showed satisfactory linearity (R > 0.99), recoveries (61.3 %-118.8 %), precision (<20 %) and limit of quantification (0.05-0.5 mg/kg). For 98 % of test dyes, screening detection limits ranged from 2.5 to 25 µg/kg. The validated method was successfully applied to real commercial foodstuffs revealing the presence of two selected illegal dyes in three samples.

Mixed hemimicelles solid-phase extraction based on sodium dodecyl sulfate-coated nano-magnets for selective adsorption and enrichment of illegal cationic dyes in food matrices prior to high-performance liquid chromatography-diode array detection detection.

In this study, mixed hemimicelles solid-phase extraction (MHSPE) based on sodium dodecyl sulfate (SDS) coated nano-magnets Fe3O4 was investigated as a novel method for the extraction and separation of four banned cationic dyes, Auramine O, Rhodamine B, Basic orange 21 and Basic orange 22, in condiments prior to HPLC detection. The main factors affecting the extraction of analysts, such as pH, surfactant and adsorbent concentrations and zeta potential were studied and optimized. Under optimized conditions, the proposed method was successful applied for the analysis of banned cationic dyes in food samples such as chili sauce, soybean paste and tomato sauce. Validation data showed the good recoveries in the range of 70.1-104.5%, with relative standard deviations less than 15%. The method limits of determination/quantification were in the range of 0.2-0.9 and 0.7-3µgkg(-1), respectively. The selective adsorption and enrichment of cationic dyes were achieved by the synergistic effects of hydrophobic interactions and electrostatic attraction between mixed hemimicelles and the cationic dyes, which also resulted in the removal of natural pigments interferences from sample extracts. When applied to real samples, RB was detected in several positive samples (chili powders) within the range from 0.042 to 0.177mgkg(-1). These results indicate that magnetic MHSPE is an efficient and selective sample preparation technique for the extraction of banned cationic dyes in a complex matrix.