A team of South African researchers at the University of Venda has now unveiled a strikingly inventive answer to that sample-preparation challenge, one that begins in an unlikely place: the bin of discarded cigarette butts. In a study published in Results in Chemistry, Herbert Musarurwa and colleagues transformed ordinary cellulose acetate cigarette filters into high-performance sorbents for microextraction by packed sorbents, or MEPS, a miniaturized cousin of conventional solid-phase extraction. The work is notable not only for its chemistry but for its rigor of self-assessment: the authors scored their method with six separate metric tools covering greenness, practicality, analytical performance and innovation, an unusually comprehensive audit for a sample-preparation protocol.

The heart of the innovation lies in a hydrophobic deep eutectic solvent, or HDES, prepared from two inexpensive and comparatively benign ingredients: menthol and salicylic acid, mixed in a 4:1 molar ratio. Deep eutectic solvents form when hydrogen-bond donors and acceptors combine into a homogeneous liquid at temperatures far below those needed to synthesize conventional ionic liquids or polymeric sorbents. In this case, the mixture was simply sonicated for thirty minutes at 70 degrees Celsius. Fourier transform infrared spectroscopy confirmed the chemistry: the hydroxyl stretching bands of the two starting materials, at roughly 3229 and 3234 inverse centimetres, shifted to 3386 inverse centimetres in the solvent, the fingerprint of an extensive hydrogen-bonding network between salicylic acid and menthol.

Coating the filters proved equally straightforward. The researchers submerged cigarette filter segments in a methanol solution of the HDES and sonicated the mixture for ten minutes at 70 degrees, then air-dried the modified filters for twenty-four hours. Infrared analysis of the coated filters showed small but telling shifts in the characteristic cellulose acetate bands, including the ester carbonyl vibration near 1733 inverse centimetres and the acetyl C–O stretch near 1228, alongside the appearance of a pronounced hydroxyl peak at 3412 inverse centimetres, together confirming that the eutectic solvent had become incorporated into the filter surface. Scanning electron microscopy revealed the practical payoff: a highly fibrous, interwoven network of well-separated cellulose acetate strands forming an open, hydrophobic architecture riddled with diffusion channels that give analytes easy access to adsorption sites.

Turning the coated filters into extraction devices required little more than a syringe. Each 10-millimetre segment of modified filter, the length that performed best in preliminary tests, was packed into a cleaned 5-millilitre syringe barrel and conditioned with methanol, which the team showed does not strip the coating because the modification itself was performed in methanol. During extraction, one gram of homogenized vegetable was vortexed with six millilitres of methanol, centrifuged, and the supernatant drawn up and expelled through the packed syringe repeatedly. Ten draw-eject cycles proved optimal, and the pumping action eliminated the need for vortex-assisted extraction, reducing energy consumption while driving efficient mass transfer of pesticides from the sample onto the sorbent. Methanol then eluted the trapped analytes for analysis by high-performance liquid chromatography with photodiode-array detection.

Optimization was carried out with genuine statistical discipline rather than trial and error. A full factorial screening design first identified which of four parameters, ionic strength, elution solvent volume, elution time and sample pH, actually mattered, with Pareto charts revealing that ionic strength dominated for fenitrothion while elution volume and pH governed chlorpyrifos extraction. A central composite design of eighteen runs then mapped the response surfaces in three dimensions. The two pesticides behaved quite differently: fenitrothion recovery climbed with increasing ionic strength up to about 12 percent, a classic salting-out effect, whereas chlorpyrifos recovery fell as salt concentration rose, presumably because excessive viscosity impedes mass transfer and can clog the sorbent pores. Both compounds degraded under alkaline conditions, so slightly acidic samples were essential. A desirability function finally reconciled the competing optima, settling on a sample pH of 6.08, an ionic strength of 10.8 percent and an elution volume of 600 microlitres for the simultaneous extraction of both pesticides.

The validated method performed credibly against far more elaborate techniques. Matrix-matched calibration curves were linear over ranges spanning roughly three orders of magnitude, with correlation coefficients between 0.9929 and 0.9993. Limits of detection ranged from 0.02 to 0.10 micrograms per gram, and limits of quantification from 0.08 to 0.29 micrograms per gram, in cucumber and tomato. Spiked samples yielded extraction recoveries between 74.8 and 90.3 percent, with enrichment factors of 7.48 to 9.03 and intra-day and inter-day precisions generally below 9 percent relative standard deviation. None of the pesticides was detected in the unspiked real samples tested. In a head-to-head comparison table, the cigarette-filter method matched or approached the sensitivity of approaches based on molecularly imprinted polymers, graphene oxide composites and kapok-fiber biochar, while posting a greener environmental profile than most of them.

That green profile was quantified rather than asserted. The Complementary Green Analytical Procedure Index pictogram was dominated by green and yellow zones, and the AGREE algorithm returned an overall score of 0.72, high for a sample-preparation method. The authors were careful to note that greenness alone does not guarantee a useful technique, so they also applied the Blue Applicability Grade Index and the Click Analytical Chemistry Index, scoring 67.5 and 78 respectively for practicality, the Red Analytical Performance Index, which returned a satisfactory 70, and the Violet Innovation Grade Index, which returned 75. The method’s main environmental liability, its reliance on offline analysis with its attendant handling steps, was mitigated by the tiny 600-microlitre elution volume, and sonication was the only energy-consuming step in the entire workflow. The extraction device itself could be reused through four adsorption-desorption cycles without significant loss of performance, and even eroded devices can reportedly be re-coated and pressed back into service.

Beyond the immediate results, the study points toward a genuinely circular form of analytical chemistry. Cigarette butts are among the most littered items on Earth, and the authors suggest that used filters, not just fresh ones, could be valorized as sorbent precursors, converting a ubiquitous waste stream into laboratory infrastructure. The extraction mechanism relies on a combination of hydrophobic interactions, ion-dipole and dipole-dipole contacts and pi-pi stacking between the aromatic pesticides and the coated filter, interactions that the hydrophobic menthol-salicylic acid solvent is ideally suited to mediate. The team acknowledges that the protocol has so far been demonstrated only for two organophosphates in two vegetables, and that multiresidue applications remain to be tested. Still, the combination of a waste-derived sorbent, a green solvent, minimal energy input and rigorous multi-metric validation offers a template for how trace analysis in food might be made both cheaper and cleaner, putting sophisticated pesticide monitoring within reach of laboratories that could never afford conventional solid-phase extraction consumables.

Subject of Research: Green microextraction of organophosphate pesticide residues from vegetables using deep eutectic solvent-modified cellulose acetate cigarette filter sorbents

Article Title: Deep eutectic solvent-modified cellulose acetate cigarette filters for the microextraction by packed sorbents (MEPS) of pesticides in vegetables: Application of green metric tools

Article References: Musarurwa, H., Tavengwa, N. T., Mokgehle, T. M., Madala, N. E., & Selahle, S. K. (2026). Deep eutectic solvent-modified cellulose acetate cigarette filters for the microextraction by packed sorbents (MEPS) of pesticides in vegetables: Application of green metric tools. Results in Chemistry, 31, Article 103927. https://doi.org/10.1016/j.rechem.2026.103927

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103927

Keywords: deep eutectic solvents, microextraction by packed sorbents, pesticide residues, chlorpyrifos, fenitrothion, cellulose acetate, cigarette filters, green analytical chemistry, HPLC, vegetables, sample preparation, AGREE metric