Efficient fabrication of pH-modified graphene nano-adsorbent for effective determination and monitoring of multi-class pesticide residues in market-fresh vegetables by GC-MS

Toxic pesticide residues in edible vegetables cause major health risks for consumers, hence quantifying them is essential. However, simultaneous and trace level determination of xenobiotic residues of various classes in complex food matrices is still a challenging analytical task. In this experiment, reduced graphene oxide (RGO-B), a carbon nano-structure with stunning adsorbent properties and ultrahigh surface area (pore size similar to 6 angstrom) was efficiently (>= 96%) synthesized via pH-controlled reduction process and characterized by ultraviolet-visible (UV-VIS) spectrophotometer, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Fourier Transform Infrared (FTIR). Adsorption efficiency of different pH-regulated RGOs was studied in terms of dye (Malachite Green) removal percentage. Two-dimensional carbon (sp(2)) RGO was used as a dispersive solid-phase extraction adsorbent in a modified QuEChERS method in combination (4:1) with primary secondary amine (PSA) to extract 28 multi-class pesticides (OC, OP, SP) from chilli, cabbage, tomato, and cucumber. The experimental results established the best extraction ability and adsorption capacity of RGO over traditional and high-cost adsorbents. Moreover, the introduction of graphene has helped improve the percent recovery (75.36-118.32%) with acceptable (<12.8%) relative standard deviation (RSD) at limits of quantification (LOQs) (S/N = 10:1) levels of 0.01-0.1 mgL(-1). Gas chromatography-mass spectrometry (GC-MS)-based multi-pesticide analytical method was successfully validated as per SANTE/12682/2019 guidelines for monitoring 144 marketfresh vegetables in West Bengal, India. The analysis results indicated that eight (8) samples (5.55%) were contaminated with toxicants 5-10 times higher than the European Union Maximum Residue Limits (EU-MRLs). Matrix removal abilities and cost analysis proved that graphene has significant prospects as an expectant nonconventional adsorbent for low-cost (53.3% cheaper) pesticide residue analysis.