In-situ hydrogen bonding driven green extraction of five Sudan dyes from tomato ketchup using thymol followed by UHPLC-PDA analysis.

We explored the potential of thymol and menthol, which are natural hydrophobic compounds containing hydrogen-bond-donor and -acceptor group, as an extractant and developed an extraction method for the simultaneous determination of five Sudan dyes in tomato ketchup. To maximize extraction efficiency, we optimized key factors that affect the extraction process. The samples were then analysed using UHPLC-PDA. Results showed that thymol provided a higher recovery compared to menthol. 1H NMR chemical shifts and 2D-NOESY spectral correlation studies confirmed the formation of hydrogen bonds between the Sudan dye and thymol, supporting a hydrogen-bonding-based extraction mechanism. The optimized method demonstrated excellent recovery at three spiked concentrations (0.05, 0.25, and 1.25 mg/kg), ranging from 81 to 108 %, with intra- and inter-day variability below 10 %. The greenness of the method, evaluated using the AGREE tool, resulted in a score of 0.62. This study thus presents a greener, reliable and cost-effective method for analysing Sudan dyes in foodstuffs.