Trace Detection of Paraquat in Tea Leaves

Importance of the Topic

Paraquat is a potent herbicide widely used to control weeds but associated with significant human toxicity and fatalities. Residual paraquat in tea leaves poses a health risk to consumers, making sensitive on-site detection essential for food safety and regulatory compliance.

Objectives and Study Overview

The primary goal was to develop a rapid, portable method for trace detection of paraquat residues in tea leaves using a Surface Enhanced Raman Spectroscopy (SERS) analyzer. Key objectives included creating a reference spectral library, determining detection limits, and validating a simplified field protocol for non-expert users.

Methodology and Instrumentation

Tea samples were spiked with known paraquat concentrations, dried at 80 °C, and extracted with chloroform. The extract was mixed with gold nanoparticle solution and sodium chloride to enhance Raman signals. Measurements were performed on-site using a portable SERS analyzer.

Used Instrumentation

• Metrohm Instant SERS Analyzer (MISA Advanced)
• MISA Vial Attachment
• ID Kit with gold nanoparticles (Au NP)
• Chloroform and sodium chloride reagents

Key experimental settings included a laser power of 5 units, 1 s integration time, and ten averaged scans with orbital raster scanning enabled.

Main Results and Discussion

The SERS method achieved detection down to 1 ng/g of paraquat in tea leaves. Baseline-corrected spectra displayed characteristic paraquat peaks, confirming sensitivity well below typical regulatory thresholds. A streamlined field protocol using disposable vials and pipettes enabled reliable on-site screening by non-specialists in under 20 minutes.

Benefits and Practical Applications

• Portable, user-friendly system for rapid contaminant screening
• Trace-level sensitivity suitable for quality control in tea production
• Minimal sample preparation and no requirement for laboratory infrastructure
• Automated data processing and library matching for clear results

Future Trends and Applications

Advancements in portable SERS technology are expected to enable multiplex detection of various contaminants. Integration with cloud-based platforms and improved nanoparticle substrates may further enhance sensitivity, data sharing, and real-time monitoring across supply chains.

Conclusion

The portable SERS approach offers a fast, sensitive, and field-deployable solution for detection of trace paraquat in tea leaves. Its simplicity and low detection limits support enhanced consumer safety and regulatory compliance.

Reference

AN-RS-025 Application Note, Metrohm AG