LC-MS/MS Analysis of Pesticide Residues in Rice and Unexpected Detection of Residues in an Organic Rice Sample

Importance of the topic

Rice is a staple food for a large proportion of the global population. Intensive cultivation of varieties such as basmati has led to widespread use of pesticides to boost yields. Monitoring residue levels is critical for consumer safety, regulatory compliance, and environmental protection. Sensitive, multi-residue analytical methods are therefore essential for routine testing of rice and other cereals.

Objectives and study overview

This work presents a streamlined LC-MS/MS protocol for the simultaneous determination of over 200 pesticide residues in rice, including conventional and organic samples. Key aims were to assess method sensitivity, recovery, linearity, and to demonstrate unexpected residue detection in an organic rice sample. The study evaluates both solvent and matrix-matched calibration, as well as a standard addition approach for accurate quantification of incurred residues.

Methodology

Samples of jasmine, basmati, and organic brown rice were ground and extracted using a modified QuEChERS procedure. Briefly, rice powder was hydrated, extracted with acidified acetonitrile, and partitioned using a commercial QuEChERS pouch. After centrifugation, extracts were dried under nitrogen, reconstituted in water/acetonitrile (1:1), and filtered prior to analysis.
Chromatographic separation employed an ACQUITY UPLC BEH C18 column (2.1×100 mm, 1.7 µm) at 45 °C with a water/methanol gradient containing 10 mM ammonium acetate (pH 5). The flow rate was 0.45 mL/min and injection volume 10 µL. MS detection used a Xevo TQD tandem quadrupole in positive electrospray mode. Multiple reaction monitoring transitions were optimized for each pesticide.
Quantification strategies included external calibration in solvent, matrix-matched calibration spanning 1.25–320 ppb, and a new standard addition feature in TargetLynx software for samples containing incurred residues.

Instrumental setup

• Extraction: Waters DisQuE QuEChERS pouches
• Liquid chromatography: ACQUITY UPLC H-Class, BEH C18 column
• Mass spectrometry: Xevo TQD, ESI+ mode
• Software: MassLynx MS, TargetLynx, Quanpedia Database
• Standards: Waters LC multi-residue pesticide kit plus additional Sigma-Aldrich compounds

Results and discussion

Linearity was excellent for nearly all compounds, with R² > 0.99 for ~85% of pesticides and > 0.98 for the remainder in both solvent and matrix. Method recoveries at 0.01 mg/kg ranged from 70–120% for 92% of analytes; 5% fell between 50–70% and 3% between 25–50%. Relative standard deviations were below 20% for most targets.
Matrix-matched calibration quantified low-level residues in several rice samples. Piperonyl butoxide appeared in two conventional basmati samples (0.0236 and 0.0054 mg/kg) and, unexpectedly, in organic brown rice at 0.0054 mg/kg. Imidacloprid and carbendazim were also detected below LOQ in multiple samples.
The standard addition approach in TargetLynx enabled accurate measurement of seven pesticides incurred in one basmati rice sample, four of which exceeded the lowest calibration point: tricyclazole (0.0113 mg/kg), propiconazole (0.0099 mg/kg), buprofezin (0.0050 mg/kg), and triazophos (0.0015 mg/kg). All detected residues remained below European MRLs.

Benefits and practical applications

• Rapid, high-throughput screening of >200 pesticides in a single LC-MS/MS run
• Quantification down to low µg/kg levels, below regulatory MRLs
• Robust recoveries and precision using a simple QuEChERS workflow
• Automated data processing and standard addition via TargetLynx for accurate incurred-residue quantitation
• Cost-effective multi-residue monitoring for food safety and QA/QC laboratories

Future trends and potential applications

Advances in high-resolution and non-targeted mass spectrometry will expand coverage to new pesticide chemistries and metabolites. Miniaturized and ambient ionization techniques may simplify sample prep. Integration of artificial intelligence and machine learning in data processing can further accelerate result interpretation. The presented workflow can be adapted to other grains, fruits, and environmental matrices to address evolving regulatory and research needs.

Conclusion

A sensitive, reliable LC-MS/MS method using QuEChERS extraction enables simultaneous analysis of more than 200 pesticide residues in rice. Excellent linearity, recovery, and precision were achieved. Routine application demonstrated detection of regulatory-compliant and unexpected residues, including in an organic sample. Automated standard addition in TargetLynx offers streamlined quantification of incurred pesticides.

Reference

1. UK Food and Environment Research Agency Horizon Scan database.
2. Pareja L., Cesio V., Heinzen H., Fernández-Alba A. R. Talanta 83(5):1613–1622 (2011).
3. Waters DisQuE brochure no. 720003048en (2012).
4. Electronic Code of Federal Regulations Title 7, Part 205, National Organic Program (2015).