Quantification of five effective components in pesticides by visible near-infrared spectroscopy

Importance of the Topic

Pesticide formulations contain active ingredients that must be accurately quantified to ensure efficacy, regulatory compliance and worker safety. Traditional methods such as reversed-phase HPLC are reliable but involve toxic solvents, extensive sample preparation and long analysis times. Visible near-infrared spectroscopy (Vis-NIRS) offers a rapid, solvent-free alternative, supporting high-throughput quality control and reducing operational costs.

Objectives and Study Overview

This study evaluates Vis-NIRS for quantifying five common pesticide actives:

• Abamectin EC (insecticide/miticide)
• Emamectin EC (lepidopteran insect control)
• Cyhalothrin EC (fast-acting neurotoxin in insect targets)
• Cypermethrin (broad-spectrum pyrethroid)
• Glyphosate (systemic herbicide/desiccant)

A set of 24–37 samples per compound was prepared across typical concentration ranges (1.5–40.5 wt-%). Calibration models were developed against HPLC reference values and validated both internally and externally.

Methodology and Instrumentation

Spectra were acquired in transmission mode over 400–2500 nm using a NIRS XDS RapidLiquid Analyzer. Samples were presented in 4 mm glass vials. Chemometric modeling employed partial least squares (PLS) regression with leave-one-out cross-validation. Key performance metrics included coefficient of determination (R2), standard error of calibration (SEC) and standard error of cross-validation (SECV).

Instrumentation Used

• NIRS RapidLiquid Analyzer (Metrohm code 2.921.1410)
• Disposable glass vials, 4 mm diameter (Metrohm code 6.7402.010)
• Vision Air 2.0 Complete software package (Metrohm code 6.6072.208)

Main Results and Discussion

Each analyte exhibited a robust calibration model with R2 values above 0.99. Optimal wavelength regions varied by compound:

• Abamectin: 1360–1850 nm and 2050–2500 nm, 2 PLS factors, SEC 0.05 %, SECV 0.06 %
• Emamectin: 1300–1790 nm, 1 factor, SEC 0.61 %, SECV 0.62 %
• Cyhalothrin: 400–1080 nm and 1300–2200 nm, 2 factors, SEC 0.05 %, SECV 0.05 %
• Cypermethrin: 1300–2200 nm, 1 factor, SEC 0.016 %, SECV 0.016 %
• Glyphosate: 1300–2170 nm, 2 factors, SEC 0.03 %, SECV 0.03 %

External validation against independent samples yielded residual errors below 0.7 wt-% and relative standard deviations typically under 4 %, demonstrating excellent agreement with HPLC.

Benefits and Practical Applications

Vis-NIRS enables rapid, non-destructive quantification of pesticide actives without hazardous solvents. The technique reduces analysis time from tens of minutes to seconds, supports inline or at-line process control and lowers per-sample costs. It is particularly advantageous for routine quality assurance in manufacturing and regulatory testing.

Future Trends and Potential Uses

• Expansion to additional pesticide classes and formulation types
• Integration with automated production lines for real-time monitoring
• Miniaturized, handheld Vis-NIR sensors for field screening
• Advanced chemometric approaches (e.g. machine learning) for improved robustness
• Combined spectroscopy techniques (e.g. Raman + NIR) for multi-component analysis

Conclusion

This application note demonstrates that Vis-NIR spectroscopy, paired with PLS regression, provides fast, accurate quantification of several pesticide active ingredients. Model performances rival conventional HPLC, offering a sustainable, high-throughput alternative for quality control in agrochemical production.

References

• World Health Organization. Pesticides.
• World Health Organization. Pesticide residues in food.
• Wikipedia contributors. Visible near-infrared spectroscopy.