Determination of Pesticide Residues in Drinking Water Using Automated Solid-Phase Extraction and Gas Chromatography with Nitrogen Phosphorus Detection

Significance of the Topic

Organophosphorus pesticides are extensively applied in agriculture to control pests and diseases. However, their residues in drinking water pose acute toxicity risks to humans and wildlife. Accurate monitoring of trace levels of these compounds is therefore critical to safeguard public health and ensure compliance with environmental regulations.

Study Objectives and Overview

This study evaluates an automated solid-phase extraction (SPE) workflow coupled with gas chromatography and nitrogen-phosphorus detection (GC-NPD) for the determination of eight organophosphorus pesticide residues in drinking water. The aim is to optimize extraction conditions, improve sensitivity, minimize solvent use and demonstrate compliance with the Chinese national method GB 5750.9-2006.

Methodology and Instrumentation

Water samples (500 mL) were spiked with a mixed standard (10 μg/mL) and fortified with 5 g of sodium chloride to enhance analyte retention. The Thermo Scientific™ Dionex™ AutoTrace 280 SPE system performed automated cartridge conditioning, sample loading, rinsing and elution using a HyperSep™ Retain PEP SPE cartridge (500 mg/6 mL). Elution employed ethyl acetate and dichloromethane in a 4 mL/4 mL/2 mL sequence, followed by concentration to 1 mL under nitrogen at 30 °C to preserve thermally labile compounds.

GC analysis was conducted on a Thermo Scientific™ TRACE™ 1310 gas chromatograph equipped with an Instant Connect split/splitless injector (250 °C) and an Instant Connect NPD detector (300 °C). A TG-1701 MS capillary column (30 m × 0.25 mm, 0.25 μm) was used with a temperature program of 80 °C (1 min), ramping at 20 °C/min to 250 °C, then 5 °C/min. Nitrogen served as carrier and make-up gas, hydrogen and air supported the detector in constant current mode.

Main Results and Discussion

Optimization experiments showed that adding 5 g NaCl per 500 mL sample maximized recoveries by reducing pesticide solubility. Elution with the selected solvent ratio achieved high extraction efficiency while minimizing solvent consumption. Linearity was excellent (R2 > 0.99) over 0.05–1.0 μg/L. Method detection limits ranged from 0.01 to 0.05 μg/L. Spike recoveries at 0.2, 0.4 and 1.0 μg/L fell between 83% and 100%, with relative standard deviations of 2.4%–8.7%, meeting routine analysis criteria.

Benefits and Practical Applications

This automated SPE-GC-NPD approach reduces manual sample handling and organic solvent use, delivering high throughput and reproducibility. Processing six 500 mL samples in parallel saves over five hours compared to traditional liquid–liquid extraction. The sensitivity and selectivity afforded by the NPD detector enable reliable monitoring of organophosphorus pesticides at sub-ppb levels in drinking water, supporting quality control in environmental and public health laboratories.

Future Trends and Opportunities

Advances in SPE sorbent materials and miniaturized extraction formats may further lower detection limits and solvent consumption. Coupling automated SPE with high-resolution mass spectrometry could expand the scope to broader pesticide classes and transformation products. Integration of on-line SPE-GC systems into fully automated workflows promises continuous monitoring capabilities for water treatment and distribution networks.

Conclusion

The described method offers a robust, sensitive and reproducible protocol for the determination of eight organophosphorus pesticide residues in drinking water, in accordance with GB 5750.9-2006. Automation of SPE and GC-NPD analysis streamlines sample preparation, reduces solvent usage and meets stringent regulatory requirements.

References

• Zhou Fang, Sun Cheng, Zhong Ming et al. Solid-phase extraction and capillary gas chromatography analysis of residual organophosphorus pesticides in water. Environ. Pollut. Control. 2005, 27(2): 151-153.
• Maciej Tankiewicz, Jolanta Fenik, Marek Biziuk. Determination of organophosphorus and organonitrogen pesticides in water samples. Trends Anal. Chem. 2010, 29(9): 1050-1064.
• Yao Chaoying, Yang Lili, Mu Yingfeng. Determination of demeton in water by gas chromatography. Sichuan Environment. 2007, 26(4): 48-50.
• Hygiene Standards for Domestic Drinking Water, Chinese Ministry of the Environment Method GB5750-2006. People’s Republic of China.