Silver Core Coated with Molecularly Imprinted Polymer as Adsorbent in Pipet-Tip Solid Phase Extraction for Neonicotinoids Determination from Coconut Water

In this work, we report an innovative adsorbent named Ag-MPS@MIP that has a core@shell structure, i.e., silver nanoparticles modified with 3-methacryloxypropyltrimethoxysilane as the core and molecularly imprinted polymer based on methacrylic acid as its shell. Thiamethoxam, imidacloprid, and acetamiprid were extracted from coconut water samples using Ag-MPS@MIP in pipet-tip solid phase, prior to high-performance liquid chromatography analysis. The separation was carried out on isocratic mode using a mobile phase consisting of C18 column (Phenomenex, 150 mm × 4.6 mm, 5 μm), ultrapure water acidified with 0.3% phosphoric acid:acetonitrile (78:22, v/v), flow rate at 1.0 mL min^–1, injection volume of 10 μL, temperature of 25 °C, and wavelength at 260 nm. The adsorbent and precursor materials were properly characterized by different instrumental techniques. The main factors affecting the recovery of analytes from coconut water samples by pipet-tip solid phase were optimized, such as sample volume (250 μL), sample pH (pH = 5.0), ionic strength (1%, m/v), washing solvent (300 μL ultrapure water), volume and type of eluent (500 μL methanol), amount of adsorbent (15 mg), cycle of percolation–dispensing (1×), and reuse (5×). Thereby, the neonicotinoids presented extraction recoveries between 82.80 and 96.36%, enrichment factor of 5, linearity ranged from 15 to 4000 ng mL^–1, correlation coefficient (r) > 0.99, limit of detection of 5 ng mL^–1, satisfactory selectivity, stability, and proper precision (RSD%: 0.52–9.64%) and accuracy (RE%: −5.19–6.45%). The method was successfully applied to real samples of coconut water.