Determination of Mercury in Plant Tissue (Vegetable Food)

Significance of the Topic

Mercury contamination in plant foods poses significant health risks to consumers. Accurate quantification of mercury in vegetable matrices is essential for food safety, regulatory compliance, and monitoring environmental exposure.

Objectives and Study Overview

This application note outlines a rapid, reagent-free protocol for direct measurement of total mercury in dried and powdered plant tissue using thermal decomposition, amalgamation, and atomic absorption spectrometry (AAS).

Methodology

1. Sample Preparation: Freeze-dry or oven-dry plant samples, grind to a fine powder, and weigh approximately 100–150 mg directly into nickel boats.
2. Blank Determination: Analyze blank nickel boats three times to eliminate residual mercury and interferences.
3. Calibration: Use certified reference materials (e.g., fly ash BCR 143r, dry sludge NIST 2781) at varying weights to establish a calibration curve spanning the expected mercury range.
4. Analysis Sequence: Automated sample loading followed by thermal drying (60 s), decomposition (200 s), and cuvette cleaning (45 s). Released mercury is trapped on a gold amalgamator and subsequently thermally desorbed for AAS detection.

Instrumentation Used

• LECO AMA254 Mercury Analyzer equipped with thermal decomposition, amalgamation, and AAS detection.
• 614-822-114 Large Nickel Boats for sample introduction.

Key Results and Discussion

Three representative plant matrices were analyzed:

• Lettuce (nominal 0.035 ppm): mean 0.0347 ppm, RSD 5.95%.
• Wheat Flour (nominal 0.015 ppm): mean 0.0154 ppm, RSD 1.34%.
• Apple Powder (nominal 0.011 ppm): mean 0.0140 ppm, RSD 4.33%.

These results demonstrate the method’s precision and accuracy within acceptable QA/QC limits for trace mercury analysis.

Benefits and Practical Applications

• Direct analysis of solid samples without chemical reagents or extensive digestion.
• Short total analysis time (approximately 8 minutes per sample) enabling high-throughput workflows.
• High sensitivity and low detection limits suitable for regulatory monitoring of food safety and environmental samples.

Future Trends and Applications

Emerging trends include integration of automated sample handling for increased throughput, expansion of the technique to diverse matrices such as soils and biological tissues, and coupling with speciation methods (e.g., GC-ICP-MS) for mercury species differentiation.

Conclusion

The thermal decomposition–amalgamation–AAS approach described here offers a reliable, rapid, and environmentally friendly solution for determining total mercury in plant-based foods, supporting regulatory compliance and public health monitoring.