Analysis of water-soluble azo dyes in soft drinks by high resolution UPLC-MS

An UPLC-Orbitrap MS system was exploited to develop and validate a method for the simultaneous determination of 11 water-soluble azo dyes (Acid Yellow 17, Acid Red 14, Acid Red 26, Acid Red 73, Acid Orange 52, Acid Orange 7, Acid Orange 12, Acid Yellow 36, Acid Orange 5, Acid Red 88 and Acid Red 9) in soft drinks. Three pairs of isomers and four disulphonated azo dyes were among a total of 11 water-soluble azo dyes obtained and purified using an SPE cartridge. They were well separated using optimized UPLC conditions with a RP18 column and a MS detector with a compatible mobile phase system. All these dyes were detected by the Orbitrap XL mass spectrometer in negative ion mode. HCD tandem MS fragment ions are first reported in this paper, and these fragment ions can be used for identification of isomers of azo dyes. According to SANCO/10684/2009, one quasi-molecular ion in full scan mode as quantification ion and one or two HCD tandem MS fragment ions as identification ions are required for compound confirmation. Matrix-matched calibration was employed for quantification. The linear matrix-matched calibration for the 11 dyes was in the range 5-200 ng g(-1) with correlation coefficients (r) of 0.9939-0.9988. Recoveries were 68.9-110.8% with coefficients of variation of 0.9-12.0%. Depending on the dye and matrix involved, the LODs were between 1.0 and 3.2 ng g(-1) and LOQs were between 5.2 and 9.8 ng g(-1).