Sustainable vortex-assisted magnetic micro-solid phase extraction using lithium ferrite/carboxylated nanodiamonds for ultra-trace determination of cadmium and lead in food and water samples.

Using a sol-gel/calcination route, a green magnetic spinel oxide/carboxylated nanodiamond hybrid (Li₂Fe₂O₄/ND-COOH) was synthesized, characterized, and applied as an efficient adsorbent for vortex-assisted magnetic micro-solid phase extraction of Cd(II) and Pb(II) prior to determination by flame atomic absorption spectrometry. Critical analytical parameters, including pH, adsorbent amount, eluent type and volume, adsorption and desorption intervals, and sample volume, were studied. The presented method achieved limits of detection of 2.3 μg L-1 for Pb(II) and 1.2 μg L-1 for Cd(II) under optimal conditions. The limits of quantification were 7.8 and 4.0 μg L-1, respectively. The preconcentration factor was obtained as 30, and the recovery range in real matrices ranged from 83% to 100%, confirming excellent accuracy. The method was efficiently employed for analyzing Pb(II) and Cd(II) in water (wastewater, tap, and spring) and food (soft drinks and fruit juices) samples.