Chemists in the United Arab Emirates have synthesized a crystalline porous material that pulls seven different carbamate pesticide residues out of fruit samples with recoveries between 92.7 and 102.9 percent, then hands them off to an ultra-sensitive detector capable of spotting traces as low as 0.01 nanograms per gram.
Carbamate pesticides are workhorses of modern agriculture. They kill pests by inhibiting the enzyme acetylcholinesterase, which disrupts nerve impulse transmission in insects. Their relatively short environmental persistence and lower toxicity compared with some other pesticide classes have made them popular, but their residues still raise concerns. As acetylcholinesterase inhibitors, carbamates can cause neurotoxicity and may disrupt immune and metabolic functions, posing chronic health risks to humans and non-target species through food chain contamination, particularly in fruits, vegetables, and dairy products. Regulatory authorities worldwide therefore set Maximum Residue Limits to control how much of these chemicals may remain in food.
Detecting those residues is harder than it sounds. Liquid chromatography coupled with tandem mass spectrometry, the gold standard for this kind of analysis, is highly sensitive and selective, but food matrices are chemically messy, and carbamates are typically present at trace levels. Direct analysis is impractical, so laboratories rely on sample pretreatment, including clean-up, extraction, and concentration steps, before the instrument ever sees the sample. The effectiveness of those steps hinges on the sorbent material used to capture the analytes. Conventional solid-phase extraction adsorbents such as C18 silica, activated carbon, and polymeric materials often lack selectivity, have low stability, and exhibit limited adsorption capacity.
Covalent organic frameworks, or COFs, are crystalline porous materials built by covalently linking organic building units into two- or three-dimensional networks. Their high surface areas, tunable pores, structural stability, and readily tailorable functionality have made them attractive sorbents for sample preparation, though relatively few have been developed specifically for analytical extraction and clean-up. Previous COF-based carbamate methods were generally limited to a small number of target compounds or a restricted range of matrices. One earlier framework, COF-TpDB, extracted four carbamates from apples and tomatoes with recoveries of 80.4 to 101.2 percent. The new work aimed to broaden both the number of pesticides and the variety of fruits that a single COF could handle.
COF-RC was synthesized through a Schiff-base condensation reaction between two organic precursors: 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 1,3,5-tris(4-aminophenyl)triazine. The reaction ran in an o-dichlorobenzene/butanol solvent mixture with 6 M acetic acid as catalyst, sealed in an autoclave at 120 °C for five days. The initially formed imine intermediates undergo enol–keto tautomerization, yielding a chemically stable two-dimensional β-ketoenamine-linked framework rich in nitrogen-containing groups, hydroxyl groups, and extended π-conjugated systems. The researchers confirmed the structure with powder X-ray diffraction, infrared spectroscopy, nitrogen sorption measurements, and thermogravimetric analysis, and they reproduced the synthesis in multiple independent batches with consistent diffraction patterns.
The characterization data reveal why the material works so well. Nitrogen adsorption measurements showed a Type I isotherm confirming microporosity, with a high BET surface area of 910 square meters per gram and a pore volume of 1.10 cubic centimeters per gram, dominated by a sharp pore-size peak at 16.0 angstroms. The diffraction pattern showed a strong peak at 2θ ≈ 6.9° plus weaker reflections, and comparison with simulated patterns indicated that the layers stack in an AB-staggered arrangement rather than eclipsed. The framework remained thermally stable up to roughly 500 °C and kept its diffraction pattern unchanged after exposure to DMSO, DMF, ethanol, acid at pH 1, base at pH 13, and boiling water.
The team probed how the material grabs its targets by studying propoxur as a representative carbamate. Infrared spectra of the loaded sorbent showed the hydroxyl stretching band shifting from 3458 to 3490 cm⁻¹ and the framework band near 1634 cm⁻¹ moving to 1644 cm⁻¹, while X-ray photoelectron spectroscopy recorded a 0.4 eV shift of the O 1s signal toward lower binding energy. No new absorption bands appeared, indicating non-covalent rather than covalent binding. The picture that emerges is of hydroxyl groups donating hydrogen bonds to the carbonyl and ether oxygens of the pesticide, framework nitrogen atoms accepting hydrogen bonds from its amino group, and π–π stacking between the pesticide’s aromatic ring and the conjugated COF backbone, with electrostatic interactions helping orient the molecules inside the pores.
Extraction conditions were optimized parameter by parameter. Methanol without formic acid proved the best elution solvent, because adding formic acid dropped carbosulfan recovery to 20 percent or less; 2.5 mL of methanol gave recoveries of 99 to 104 percent. Salt addition made no difference, with recoveries of 96 to 103 percent across 0 to 20 percent NaCl, so no salt was used. The optimum pH was 6 to 7, the optimum sorbent amount 10 mg, the optimum adsorption time 30 minutes, the optimum desorption time 15 minutes, and the optimum shaking speed 400 rpm. In competitive experiments against eight organophosphate pesticides chosen as potential interferents, the carbamates were recovered at 94.7 to 101.8 percent while the organophosphates managed only 1.7 to 67.7 percent, demonstrating preferential extraction of the target class.
Validation across the four fruit matrices showed calibration curves with coefficients of determination between 0.9985 and 0.9997, detection limits of 0.0101 to 0.051 ng/g, and quantification limits of 0.0305 to 0.1545 ng/g. Repeatability relative standard deviations ranged from 1.55 to 7.82 percent and intermediate precision from 0.38 to 9.42 percent. Most analyte-matrix combinations showed negligible matrix effects within ±20 percent, though moderate ion enhancement appeared for pirimicarb in dates and tomatoes and fenoxycarb in dates, and fenoxycarb showed moderate suppression in apples, supporting the use of matrix-matched calibration. Spiked samples at 0.5, 10, and 100 ng/g, each in five replicates, met the acceptance criteria of the European SANTE/11312/2021 guidelines in every matrix.
Applied to unspiked market samples, the method found real residues. Fenoxycarb at 3.27 to 10.02 ng/g and propoxur at 0.76 to 6.02 ng/g were the most frequently detected, followed by carbofuran at 0.12 to 3.32 ng/g in dates, apples, and tomatoes, carbosulfan in one date and two tomato samples, pirimicarb at 0.34 to 0.40 ng/g in dates, apples, and grapes, and bendiocarb and methiocarb only in grapes and tomatoes at low levels. The sorbent retained 90 to 103 percent recovery through ten reuse cycles, with a gradual decline afterward; propoxur fell to 58 percent by cycle fifteen while the others remained acceptable, and diffraction and infrared checks after ten cycles showed the crystalline framework and its functional groups essentially unchanged. Compared with previously reported sorbents, the method combines low detection limits, a modest 10 mg sorbent dose, 2.5 mL of solvent, and seven simultaneous targets, which the authors suggest makes it a practical candidate for routine pesticide residue monitoring in food safety laboratories.
Subject of Research: Development of a covalent organic framework sorbent for solid-phase extraction of carbamate pesticide residues in fruit samples
Article Title: Facile synthesis of a covalent organic framework for efficient solid-phase extraction and analysis of carbamate pesticide residues in fruits
Article References: Morsi, R., AlNeyadi, S. S., Al-Meetani, B., Shekhah, O., & Meetani, M. A. (2026). Facile synthesis of a covalent organic framework for efficient solid-phase extraction and analysis of carbamate pesticide residues in fruits. Food Chemistry: X, 40, Article 104666. https://doi.org/10.1016/j.fochx.2026.104666
Image Credits: AI Generated
DOI: 10.1016/j.fochx.2026.104666
Keywords: covalent organic frameworks, solid-phase extraction, carbamate pesticides, UHPLC-MS/MS, food safety, pesticide residues, fruit analysis, sample preparation, porous materials, residue monitoring, Facile, synthesis
News Source: Bethany Barker. (October 29, 2026). New Covalent Organic Framework Extracts Seven Carbamate Pesticides from Fruit. Scienmag.
