Cu- and S- @SnO2 nanoparticles loaded on activated carbon for efficient ultrasound assisted dispersive µSPE-spectrophotometric detection of quercetin in Nasturtium officinale extract and fruit juice samples: CCD-RSM design

A simple, rapid, and efficient method of dispersive micro solid phase extraction (D-μ-SPE) combined with UV–Vis spectrophotometry via ultrasound-assisted (UA) was applied for the determination and preconcentration of quercetin in extract of watercress (Nasturtium officinale), fruit juice and water samples. The sorbent in this method was synthesized by doping copper and sulfide into the tetragonal structure of SnO₂-nanoparticles (Cu- and S- @SnO₂-NPs) and subsequently loading it on activated carbon (AC). The D-μ-SPE parameters with direct effect on the extraction efficiency of the targeted analyte, such as sample pH, volume of eluent, sorbent mass and ultrasound time were optimized using central composite design method. Under optimized conditions, the calibration graph for quercetin was linear in the range of 20–4000 ng mL⁻¹; the limit of detection and quantitation were 4.35 and 14.97 ng mL⁻¹, respectively and the enrichment factor was 95.24. Application of this method to analyze spiked extract, fruit juice and water samples resulted in acceptable recovery values ranging from 90.3% to 97.28% with intra-day and inter-day relative standard deviation values lower than 6.0% in all cases. Among the equilibrium isotherms tested, Langmuir was found to be the best fitted model with maximum sorption capacity of 39.37 mg g⁻¹, suggesting a homogeneous mode of sorption for quercetin.