Hollow Fiber-Supported ZIF-8@GO Reinforced Sol-Gel for Preconcentration of Paraquat Before Determination by UV-Vis Spectrophotometry.

A novel, sensitive, and efficient method was developed for the determination of paraquat in soil samples, centered on solid-phase microextraction using hollow fiber-supported ZIF-8@GO reinforced sol-gel combined with UV-Vis spectrophotometry at 257 nm. Silica-based ZIF-8@GO was synthesized through sol-gel technology by reacting tetraethyl orthosilicate (TEOS) with hydrochloric acid (HCl) as a catalyst. The resulting solution was injected into hollow polypropylene fiber segments for in situ gelation. Key microextraction parameters, such as the donor phase pH and volume, stirring rate, extraction time, and desorption conditions (solvent type and volume), were systematically studied and optimized. Under optimal conditions, the method demonstrated linearity within the range of 0.5-2000 μg L, with a correlation coefficient of 0.999. The relative standard deviation for seven replicate measurements at a concentration of 600 μg L paraquat was 0.4%. A preconcentration factor of 631 and a detection limit of 0.15 μg L were achieved. Validation of the method was conducted by analyzing soil samples from various sites, yielding recoveries between 96% and 105% with low relative standard deviations, indicating its high accuracy and reliability in detecting trace levels of paraquat.