Chromatography Method Detects Ten Pesticide Residues in Capsicum Samples

A new open-access study published in EPJ Techniques and Instrumentation describes a chromatography-based workflow for detecting pesticide residues in agricultural products, using capsicums sold in Haidong City, Qinghai Province, China, as its test case. The research, led by Yujie Wang and published on 5 June 2025, combined a widely used sample preparation technique known as QuEChERS with gas chromatography-tandem mass spectrometry, or GC-MS/MS, to measure ten kinds of organophosphate pesticides, commonly abbreviated as OPPs. The work was motivated by a practical regulatory question: whether capsicum products reaching local farmers’ markets comply with China’s national limits on pesticide residues, and whether a single, streamlined laboratory method could answer that question reliably enough for routine safety supervision.

The study’s central finding is twofold. First, after systematic optimization of the extraction solvent and the purification agent, the method achieved average recovery rates between 75.94% and 118.78% across the ten target pesticides, with relative standard deviations ranging from 1.01% to 3.25%, figures the author presents as evidence of good recovery and small measurement error. Second, when the optimized method was applied to 216 real capsicum samples from farmers’ markets in Haidong City, only one pesticide, methidathion, was detected, and it was found just twice. The detected concentrations ranged from 0.0018 to 0.0026 mg/kg, far below the maximum residue limit of 0.2 mg/kg set under China’s National Food Safety Standard for Maximum Residue Limits of Pesticides in Food, GB2763-2021. All ten organophosphate pesticides tested remained within the standard limits.

The choice of capsicum as the study subject reflects both its agricultural importance and its exposure profile. According to the paper, capsicum is a commonly used agricultural product with high nutritional value, and during cultivation producers often apply many pesticides in order to avoid damage from aphids and mites. That intensive treatment regime makes capsicum a sensible sentinel crop for residue monitoring. The author frames the resulting method as a form of support for the safety supervision of capsicum in Haidong City, and more broadly as an approach that could be applied to safety testing of additional agricultural products.

Understanding the significance of the analytical results requires some background on the pesticides themselves, which the paper provides. Pesticides can be divided by use into categories such as insecticides and herbicides, and by chemical composition into several main types. Organophosphate pesticides, the focus of this study, are described as the type used the most in practice. The paper also lists organochlorine pesticides, which contain chlorine and are described as highly toxic, and carbamates, which follow the RO(CO)NRR chemical pattern and have relatively low toxicity. The persistence of residues after pesticide application is the core concern: the paper notes that long-term exposure to food carrying excessive pesticide residues can lead to health issues such as fatigue and headaches, and that residues entering the human body through food can affect immune function and the nervous system, causing headache, nausea, and diarrhea, with potential damage to vital organs in severe cases.

The environmental dimension of pesticide use also features in the study’s motivation. Pesticides remaining on the surface of crops can enter soil and groundwater through precipitation and irrigation, threatening the organisms living in those environments, and residues generated by pesticide spraying can also pollute the atmosphere. The paper observes that excessive pesticide use remains common at present, driven by the pursuit of higher yields, while most pesticides have high toxicity. Together, these human-health and environmental considerations underpin the argument that safety detection of agricultural residues is very important, and that chromatography-based detection methods currently enjoy a very wide range of applications.

On the preparation side, the study situates QuEChERS, which stands for quick, easy, cheap, effective, rugged, and safe, among several established pre-treatment options. Solid phase extraction uses solid adsorbents to achieve separation and offers high sensitivity. Solid phase microextraction uses quartz fiber as a carrier and requires no additional solvent, but its extraction coating is expensive and fragile. Gel permeation chromatography uses organic solvents and hydrophobic gel macromolecules to achieve separation in an environmentally friendly manner, though it consumes large amounts of organic solvent. Liquid phase microextraction relies on liquid-liquid interaction and features simple operation and high efficiency. QuEChERS extraction achieves separation based on a single acetonitrile solvent, with simple operation and good safety. The paper notes that solid phase extraction and QuEChERS are the most widely used in practice, and that QuEChERS has the advantage of being fast and simple, which is why it was selected for pre-treatment in this work.

On the detection side, the paper reviews the main chromatography-based options before settling on GC-MS/MS. Gas chromatography vaporizes a mixture at high temperature, separates its components in a chromatographic column using inert gases, and can employ a variety of detection devices such as the nitrogen phosphorus detector and the flame photometric detector; it offers high sensitivity and speed but is not suitable for substances with high boiling points. High performance liquid chromatography uses mobile phases of different polar liquids and suits substances with high boiling points. Gas chromatography-mass spectrometry combines the separating power of gas chromatography with the identification power of mass spectrometry, and tandem configurations such as GC-MS/MS have higher sensitivity than single-stage mass spectrometry. Liquid chromatography-mass spectrometry performs well with polar, unstable compounds and can detect almost any compound. The author identifies GC-MS/MS as the most widely used method in the safety detection of pesticide residues and therefore the one studied here.

The experimental workflow is described in detail. Capsicum samples totaling 1.5 kg were chopped, crushed with a processor, and stored at minus 20 degrees Celsius. A 2 g portion was placed in a 50 mL centrifuge tube, mixed with 10 mL of ultra-pure water and stirred strongly for two minutes, then combined with 15 mL of acetonitrile-acetic acid solution, 1.5 g of sodium acetate, and 6 g of anhydrous magnesium sulfate. The mixture underwent fifteen minutes of vibration and fifteen minutes of ultrasonic treatment, followed by centrifugation at 4500 r/min for five minutes. Eight milliliters of supernatant were transferred to a 15 mL centrifuge tube containing purification agents, centrifuged again, and a 2 mL aliquot of the resulting supernatant was concentrated to near dryness by nitrogen blowdown at 40 degrees Celsius before being reconstituted with chromatographically pure acetone for testing. Standard solutions were prepared by diluting ten single-standard reserve solutions of 10 μg/mL into a 1 μg/mL mixed standard reserve solution, also stored at minus 20 degrees Celsius.

Two optimization experiments shaped the final method. Comparing acetone, ethyl acetate, and 1% glacial acetic acid-acetonitrile as extraction solvents, the acetic acid-acetonitrile option performed best: among its ten recovery results, two fell between 70% and 80%, four between 80% and 100%, three between 100% and 120%, and one exceeded 120%, whereas acetone and ethyl acetate produced cases below 70% and no cases above 120%. A parallel comparison of three purification agent combinations built around magnesium sulfate, PSA, C18, and GCB showed that 0.6 g MgSO4 plus 0.1 g PSA plus 0.1 g GCB yielded only one recovery between 70% and 80%, five between 80% and 100%, three between 100% and 120%, and one above 120%, outperforming the alternatives, which each produced two recoveries below 80% including cases under 70%. Recovery and precision were then assessed by spiking blank capsicum samples with the mixed standard solution at levels of 10, 20, and 100 μg/kg.

The author concludes that the designed safety detection method showed good recovery, small errors, and strong usability, that no excessive pesticide was detected in the real products tested, and that Haidong City currently has good control over pesticide use in capsicum, which should be maintained. The method, the paper states, can detect the ten target organophosphate pesticides in agricultural products and can be applied in practice, including to a wider range of agricultural product safety testing. As with any single-market surveillance dataset, the 216-sample result describes the products actually tested in Haidong City rather than a national picture, but the combination of a validated analytical workflow and clean surveillance outcomes offers a concrete template for residue monitoring programs elsewhere.

Subject of Research: Detection of organophosphate pesticide residues in capsicum using QuEChERS extraction and gas chromatography-tandem mass spectrometry

Article Title: Study on the safety detection of pesticide residues in agricultural products by means of chromatography

Article References: Wang, Y. (2025). Study on the safety detection of pesticide residues in agricultural products by means of chromatography. EPJ Techniques and Instrumentation, 12(1), Article 3. https://doi.org/10.1140/epjti/s40485-025-00116-4

Image Credits: AI Generated

DOI: 10.1140/epjti/s40485-025-00116-4

Keywords: pesticide residues, organophosphate pesticides, QuEChERS, GC-MS/MS, gas chromatography, mass spectrometry, capsicum, food safety, maximum residue limits, Haidong City, agricultural products, chromatography