Fast Simultaneous Determination of Eight Sudan Dyes in Chili Oil by Ultra-High-Performance Supercritical Fluid Chromatography

Supercritical fluid chromatography for the analysis of natural dyes: From carotenoids to flavonoids

Plant-derived natural dyes are used in a variety of formulated products, from food to cosmetics and pharmaceutics. In addition to their color, they also provide some bioactivity. While they are mostly analyzed with high-performance liquid chromatography, supercritical fluid chromatography was also employed for several dye families, mostly for carotenoids and chlorophylls, and more recently for anthraquinones and flavonoids. These supercritical fluid chromatography methods are described in this review. Because the dyes have different structures and structural variations (polarity, isomers, etc.), the best chromatographic system to achieve their separation is not always the same. Hydrophobic stationary phases are preferred for the most hydrophobic dyes (chlorophylls and carotenoids) while polar stationary phases are preferred for the polar dyes (anthraquinones and flavonoids). Regarding the mobile phase composition, chlorophylls and carotenoids are best eluted with moderate proportions of co-solvent in CO₂ (about 40%), while the most polar glycosylated flavonoids require higher proportions of co-solvent and acidic additives. Because dyes are colorful, ultraviolet-visible detection is often sufficient, while mass spectrometry offers additional structural information. Furthermore, fundamental information can also be gained through chromatographic analysis of dyes: either solubility in supercritical fluids, in view of their extraction, or retention behavior providing an understanding of stationary phase properties.

Unified chromatography - Mass spectrometry as a versatile tool for determination of food dyes

Unified chromatography with mass spectrometric detection was assessed for determination of food dyes. Nineteen substances representing azo, triphenylmethane, xanthone, indigoid, quinoline and polyene classes covering an unprecedented range from nonpolar β-Carotene (logD 13.6) to ionic Tartrazine (logD -7.5) were analyzed simultaneously. The dyes were separated in a single experimental run by an 18-min gradient elution from 98% CO₂ to 100% aqueous-methanolic modifier on a diol column. Isomeric substances were resolved, and Isatin Sulfonic acid was detected as a degradation product of Indigo Carmine. Mobile phase properties reproducibly changed from supercritical to liquid state ensuring stable retention times (inter-day RSD<0.5%). Quantitative analysis of sports drinks after straightforward 10- or 25-fold dilution with dimethyl sulfoxide confirmed the method applicability to real-life samples. Sufficient limits of detection (typically 0.025 mg L^-1 in processed samples, equivalent to 0.25 mg L^-1 in drink) and a wide linear range (typically 0.5-50 mg L^-1 or 1.3-125 mg L^-1 in drink for 10× or 25× dilution, respectively) were demonstrated during validation. A comparison of method performance with competitive liquid chromatography procedures is also provided. Unified chromatography is a promising tool for comprehensive multiclass analysis of dyes in the context of food safety.

Fast, easy, cheap, robust and safe method of analysis of Sudan dyes in chilli pepper powder

Illicit use of Sudan dyes, a group of harmful and carcinogenic azo dyes, in the food industry has taken a surge in various parts of the world, especially in Africa. Their use in food as additives pose a dire health risk to consumers and have been banned by various food regulatory bodies worldwide. To help increase surveillance, various methods have been proposed for their analysis in literature. This study also sought to experiment and propose an alternative method for quick, easy, cheap, robust and ecologically safe analysis of Sudan dyes in chilli pepper powder and similar matrices. The optimized method used a 6.0 mL mixture of acetone:acetonitrile (1:5 v/v) solvent in a modified QuEChERs method for extraction of Sudan dyes I-IV. The simultaneous analysis of the dyes were achieved on Shimadzu prominence UFLC 20AD coupled with SPD 20AX UV detector operated at dual wavelength of 500 and 480 nm. A total of twenty four (24) chilli pepper powder samples from eight different vendors on the Ghana market were analysed using the optimized method. Quantitation of analytes were done using the external standard calibration method with determination coefficient, R² > 0.9999. The limit of detection (LOD) and limit of quantitation (LOQ) of the method were 0.02–0.04 mg/kg and 0.05–0.13 mg/kg respectively. A good recovery range between 85.3 – 121.2% were obtained for a spike level of 1.0 mg/kg in real samples. ANOVA analysis at 95% CL showed statistically no significant difference (p > 0.05) in the recoveries between samples and also between the individual compounds. The method experimented and proposed in this study is fast, easy, cheap, robust and ecologically safe, presenting an alternative method for routine analysis for increased rate of surveillance against the illicit use of Sudan dyes as food additives.