Natural deep eutectic solvent–based magnetic nanofluid microextraction for sensitive determination of cadmium in tap water and tea leaves by GFAAS

A novel analytical method was developed for the determination of cadmium in tea samples using a natural deep eutectic solvent-based magnetic nanofluid liquid phase microextraction technique, combined with graphite furnace atomic absorption spectrometry. In this study, cadmium forms a neutral and hydrophobic complex with dithizone, which is subsequently extracted by the magnetic nanofluid prepared through the dispersion of Fe₃O₄ nanoparticles in a natural deep eutectic solvent composed of l-menthol and formic acid. The method demonstrated excellent analytical performance, with limits of detection (LOD) and quantification (LOQ) of 0.0060 and 0.018 ng/L, respectively. The linearity range of the NADES-MNF-LPME–GFAAS method was 0.018 to 0.20 ng L. The concentrations of cadmium in the real samples ranged from 0.08 to 1.05 ng/L in tap water samples and from 0.03 to 0.19 ng/L in tea leaf samples, respectively. Cadmium was successfully quantified in real samples with recoveries of 80–120%. Interference from coexisting ions was also evaluated to ensure method selectivity. Finally, statistical comparison of t-values between the proposed method and both Thailand Reference Material and standard reference materials showed no significant differences at the 95% confidence level (df=2), confirming the method’s reliability and suitability for cadmium contamination assessment in food.