Agrochemicals and pesticides testing determines the identity and concentration of pesticide residues and related agrochemical compounds in food, agricultural produce, soil and water. Testing typically follows a two-tier structure: rapid screening by immunoassay and spectrophotometry, followed by confirmatory analysis using gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–tandem mass spectrometry (LC-MS/MS). The modules below describe the scope of testing, sample collection practice, screening and confirmation procedures, assay performance indicators, and the comparison of results against maximum residue limit (MRL) requirements. Together they form a complete workflow from sample receipt to a defensible compliance judgement.
Scope and significance
Pesticide residue testing covers active substances, metabolites and degradation products arising from insecticides, herbicides, fungicides, acaricides and plant growth regulators. Depending on the chemical class, target analytes include organophosphorus, organochlorine, pyrethroid, carbamate and neonicotinoid compounds, together with polar pesticides such as glyphosate. The significance of this testing is threefold. First, it verifies that residues in food and feed remain within statutory MRLs, protecting consumer health and enabling market access. Second, it monitors environmental compartments such as soil, groundwater and surface water, where persistent compounds may accumulate. Third, it supports traceability in supply chains: growers, processors and exporters rely on residue data to document good agricultural practice and to satisfy import controls in destination markets.
Sample types and collection
Sample matrices span fresh fruits and vegetables, grains and cereals, tea and herbal materials, animal-derived foods, drinking and irrigation water, and soil. Because residues are often unevenly distributed, sampling must follow recognised protocols for lot representation; a composite laboratory sample is typically prepared from multiple incremental portions drawn across the lot. Cold-chain transport is required for perishable produce, since enzymatic degradation can alter residue levels before analysis. On receipt, the laboratory records sample condition, mass and temperature, then homogenises the material, usually by chopping and freezing before cryogenic milling. Representative test portions are withdrawn for extraction, while reserve portions are retained for repeat or referee analysis. Chain-of-custody documentation must remain intact from field to bench, as incomplete traceability can invalidate otherwise sound analytical data.
Residue screening by ELISA and spectrophotometry
Screening methods are selected for throughput and cost, allowing large sample numbers to be triaged before instrumental confirmation. ELISA kits employ antibodies raised against a target compound or class; pesticide residues in the extract compete with immobilised antigens for antibody binding, and the colour intensity measured at an appropriate wavelength is inversely related to concentration. Spectrophotometric approaches include enzyme-inhibition assays for organophosphorus and carbamate insecticides, which measure the suppression of acetylcholinesterase activity through changes in absorbance. Operational points deserve attention: matrix effects and cross-reactivity can bias immunoassay readings, so extracts may require dilution or cleanup before measurement. Calibration curves, blank controls and spike checks should accompany each plate or batch. Positive or suspect results are flagged and routed to confirmatory analysis rather than reported quantitatively.
Confirmation and quantification by GC-MS and LC-MS/MS
Confirmation relies on chromatographic separation coupled with mass-spectrometric detection. GC-MS, frequently operated in single-quadrupole or GC-MS/MS mode, suits semi-volatile, thermally stable compounds such as organochlorines, pyrethroids and many organophosphates; separation is performed on non-polar or mid-polar capillary columns. LC-MS/MS with electrospray ionisation handles polar, thermolabile and high-molecular-weight pesticides, including carbamates, neonicotinoids and glyphosate. Extraction commonly follows the QuEChERS procedure: salting-out acetonitrile extraction, followed by dispersive solid-phase cleanup with sorbents such as graphitised carbon black and primary–secondary amine. Quantification uses matrix-matched standards or isotopically labelled internal standards to correct for ion-suppression effects. Identification criteria include retention-time agreement, qualifying ion ratios and signal-to-noise, so that reported results meet recognised identification-point requirements.
Assay performance: sensitivity, recovery and repeatability
Method performance is judged against validated metrics rather than a single reading. Limit of quantification (LOQ) must sit below the relevant MRL for each analyte–matrix pair; otherwise a compliant result cannot be distinguished from analytical noise. Recovery studies, performed by fortifying blank matrix at multiple levels, indicate extraction efficiency and bias, and common validation frameworks accept recovery within defined ranges that widen at trace levels. Repeatability, expressed as relative standard deviation under within-run conditions, and reproducibility between runs or analysts reflect precision. Matrix effects are assessed by comparing solvent and matrix-matched calibration slopes, with compensation through internal standards where suppression exceeds tolerance. Proficiency testing participation and routine quality controls — blanks, duplicates and continuing calibration verification — demonstrate that the method remains in statistical control over time.
Co-testable parameters and MRL compliance
Residue testing is frequently combined with related determinations on the same sample. Multi-residue methods can incorporate several hundred analytes in one injection sequence, and additional parameters such as heavy metals, mycotoxins, nitrates or dithiocarbamate residues may be co-requested under one testing programme. On completion, quantitative results are compared with the applicable MRLs, which differ between jurisdictions and commodity groups; the strictest limit typically governs when produce moves across several markets. Results reported as below LOQ are assessed against the limit, while detections above MRL constitute non-compliance requiring notification and, where necessary, confirmatory re-analysis of the reserve portion. Reporting should state the method used, LOQ, measurement uncertainty and the regulatory reference applied, so that clients and regulators can interpret the data without ambiguity. Agrochemicals and pesticides testing combines rapid screening (ELISA, spectrophotometry) with confirmatory quantification by GC-MS and LC-MS/MS across food, water and soil matrices. A validated workflow — representative sampling, QuEChERS extraction, matrix-matched calibration and documented quality control — delivers LOQs below regulatory limits, verifiable recovery and repeatability, and clear comparison against jurisdiction-specific MRLs, supporting compliance decisions for growers, processors and exporters.