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

Abstract

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).

Quantification of synthetic food dyes in beverages or pharmaceutical tablets by solid phase extraction (spe) followed by UV/VIS spectrophotometry

“…In the majority of published studies synthetic dyes are subjected to SPE on C18, Amberlite XAD-2, polyamide or polyamide foam [3,6,7,11,26,32,33] -supports dedicated primarily to separation of neutral molecules of different polarity and size. Anions of carboxylic or sulfonic acids can be effectively separated on anion exchange sorbents [4,7,33,35]. Retention of an analyte, bearing a negative charge, requires a positively charged anion exchange sorbent to ensure suitable ionic interactions.…”

“…In previously published papers on isolation of synthetic food dyes on WAX type sorbents both strategies of elution were presented and the solutions used as eluents were either acidic (to neutralize the positive charge on the sorbent) or basic (to neutralize the negative charge on the analyte), respectively [4,33]. After the SPE extraction chromatographic (TLC [4] or UPLC [33]) determination of isolated dyes followed.…”

“…We have decided that prior to the spectrophotometric determination the synthetic dyes analyzed in this study should be isolated by solid phase extraction on the WAX type aminopropyl sorbent with basic rather than acidic elution. This step can be achieved with aqueous sodium hydroxide [35] or methanolic ammonia [33] but such conditions are not particularly mild. In the course of this study the solutions of selected organic bases (morpholine, imidazole, triethanolamine, aminopropylmethanol) were tested in search for mild yet effective conditions.…”

“…Prior to further analysis sample pretreatment is usually needed. Dyes are often isolated by separation techniques such as ion-pair extraction [24,31] or solid phase extraction (SPE) [3,4,6,7,11,26,32,33]. The sorbent most commonly used for SPE of synthetic dyes is RP-18 [3,7,11], but other supports such as cotton [6], Amberlite XAD-2 [7], polyurethane foam [26], polyamide [7], N-vinylpyrrolidone and divinylbenzene copolymer [32], neutral primary amine modified divinyl benzene polymer [33] or amino-modified silica [4] have also been used.…”

Future perspectives in Orbitrap™-high-resolution mass spectrometry in food analysis: a review

“…The measured product ion and the unique neutral loss (C 4 H 7 N 3 ) provided important additional information which led from a suspected elemental composition to the elucidation of the correct chemical structure.Ruf et al, (2012) note that searches based on a known elemental composition almost always lead to a huge number of possible chemical structures, and it is therefore Downloaded by [New York University] at 06:be able to limit the search down to a single surviving elemental composition. A method combining QuEChERS extraction and clean-up with UHPLC-Q-Exactive™ has been extensively validated for the screening and identification of 69 dyes in wines(Jia et al,2014), although there was no evidence that adulteration of wines with illegal dyes is occurring in practice Liu et al, (2011). have established a simple and highly sensitive UPLC-Orbitrap MS method with matrix-matched calibration for simultaneous determination of 11 watersoluble azo dyes in soft drinks, although the authors did not indicate if they were seeking to detect illegal use of non-permitted dyes.The deliberate adulteration of herbal products or dietary supplements with synthetic chemicals, which are either approved pharmaceuticals or unauthorised analogues of known bioactive substances has become widespread in recent years Lebel et al, (2014).…”