Rapid Quantification of Polar and Semipolar Pesticide Metabolites with Combined Online SPE and Direct Injection

Significance of the Topic

The analysis of pesticide metabolites in water sources is critical for environmental monitoring, regulatory compliance, and public health protection. Polar and semipolar metabolites can co-occur at trace levels, demanding analytical strategies that combine high sensitivity with broad chemical coverage.

Study Objectives and Overview

This study developed a unified online solid phase extraction (SPE) coupled with direct injection LC-MS/MS method to simultaneously quantify 26 polar and semipolar pesticide metabolites in drinking water. The approach aimed to streamline sample preparation by employing a single automated run that enriches semipolar compounds and directly injects polar analytes for detection.

Methodology and Instrumentation

• Instrumentation: Agilent InfinityLab Online SPE system with two alternating PLRP-S cartridges, each fitted with a 5 mL high-volume loop and a 100 µL loop for polar analytes.
• Chromatography: C18 column (100 × 3 mm, 2.7 µm) with a 28 min gradient from 0 % to 99 % organic phase at 500 µL/min and 45 °C.
• Mass Spectrometry: Triple quadrupole in MRM mode for sensitive and selective quantitation.
• Solvents and Standards: MS-grade acetonitrile, methanol, water, ammonium formate, formic acid; target analytes spiked at sub-ng/L levels.
• Workflow: Loading of 6 × 900 µL sample onto SPE, 100 µL direct injection, backflush elution, cartridge cleaning and conditioning.

Main Results and Discussion

The modified SPE setup achieved enrichment factors between 10 and 90, lowering limits of quantitation to 0.01–5 ng/L for most metabolites. Calibration curves displayed excellent linearity (R2 > 0.99) across 0.01–500 ng/L. Precision assessments yielded area RSDs < 9 % and retention time RSDs < 1.3 %. The total run time for sample loading, enrichment, and separation was 28 min. Improved peak shapes were observed for early eluting polar metabolites compared to direct injection alone.

Benefits and Practical Applications

• Single-run analysis reduces total analysis time and labor by combining polar and semipolar targets.
• Sub-ng/L sensitivity supports compliance with stringent drinking water regulations.
• Automated alternating cartridge operation enhances sample throughput and minimizes carryover.

Future Trends and Prospects

• Integration with high-resolution mass spectrometry for non-target metabolite screening.
• Expansion to diverse environmental matrices and complex sample types.
• Miniaturization of SPE components to reduce solvent use and improve sustainability.

Conclusion

The combined online SPE and direct injection method offers a rapid, automated, and highly sensitive platform for the simultaneous quantification of polar and semipolar pesticide metabolites in aqueous samples. Its broad analyte coverage and sub-ng/L detection capability make it a valuable tool for environmental and water quality monitoring.

References

1. Rubirola A, et al. Multiresidue analysis of 24 Water Framework Directive priority substances by on-line solid phase extraction-liquid chromatography tandem mass spectrometry in environmental waters. J Chromatogr A. 2017;1493:64–75.
2. Schuhn B. High Volume Injection up to 5 mL with the Agilent 1200 Infinity Series Online SPE Solution for Highest Sensitivity. Agilent Technologies Technical Overview. 2013;5991-3173EN.