Ultrasensitive quantification of illegal cationic dyes in foods with low matrix effects: Carboxyl-functionalized COFs as novel adsorbents and MALDI-TOF MS matrices

Carboxyl-functionalized covalent organic framework (COF HD ) was synthesized and successfully applied as both an adsorbent and MALDI-MS matrix for the ultrasensitive detection and quantitative analysis of illicit cationic dyes in food samples with low matrix effects. Benefitting from its great thermal stability and strong UV absorption properties, COF HD was an ideal matrix for cationic dyes with no matrix background interference, high ionization efficiency, excellent salt tolerance, and superior reproducibility. Furthermore, the merits of numerous adsorption sites, good water dispersibility, and electronegative natures facilitated the efficient and selective enrichment of cationic dyes from solutions. The proposed method was further applied for the quantitative analysis of CV and RB in real food samples, such as chili, red wine, beverage samples, exhibiting a wide linear range (0.2–40 ng mL −1 for CV and 0.8–200 ng mL −1 for RB with R 2  > 0.98), ultra-high sensitivity (at subppt levels), excellent precision and accurate, satisfactory recovery, and low matrix effects (91.7 %–96.8 %). This work establishes a robust, high-throughput analytical platform for the sensitive detection and precise quantification of illicit cationic dyes in complex food matrices, providing a reliable tool for food safety monitoring.