High Sensitivity Determination of Lead in Soy sauce

Significance of the Topic

This study addresses the accurate measurement of trace lead in soy sauce, a complex fermented condiment high in salts and sugars. Ensuring low levels of heavy metals in food products is critical for consumer safety and compliance with national and international standards such as GB 2762-2017.

Objectives and Study Overview

The primary goal was to develop and validate a robust graphite furnace atomic absorption spectrometry (GFAAS) method using the Agilent 280Z instrument with an Omega platform tube for the quantification of lead in soy sauce. Key objectives included optimizing furnace parameters, evaluating method sensitivity and precision, and demonstrating reproducibility across multiple laboratories.

Methodology and Instrumentation Used

Reagents and sample preparation were standardized to minimize matrix effects and ensure operator safety. Key steps and equipment:

• Instrument: Agilent 280Z GFAAS with Transverse Zeeman background correction, Omega platform tube, PSD 120 autosampler, and Tube-CAM viewing camera.
• Modifier solution: 1% magnesium nitrate and 0.2% palladium nitrate in 1% HNO3.
• Calibration standards: 0 to 40 µg/L Pb prepared from a 1000 mg/L stock using the autosampler.
• Sample preparation: 0.10 g soy sauce diluted to 5.0 g with 1% HNO3 (50× dilution) and vortex mixed.
• Furnace program: Multistep heating with drying (95–500 °C), ashing at 805 °C, and atomization at 2132 °C, optimized via Surface Response Methodology (SRM) Wizard.

Main Results and Discussion

Optimization with the SRM Wizard yielded ash and atomization temperatures of 805 °C and 2132 °C, respectively, maximizing absorbance and minimizing variability. The calibration curve demonstrated excellent linearity (R² > 0.9996). The characteristic mass for Pb was 22.3 pg at a 10 µL injection, indicating high sensitivity. Method detection limits were 0.35 µg/kg in solution and 18 µg/kg in the final sample, well below the 1000 µg/kg regulatory limit. Robustness was confirmed across four independent centers, achieving recoveries of 94–102% and RSDs below 2%.

Benefits and Practical Applications

The validated method provides laboratories with a highly sensitive, accurate, and precise means to monitor lead in challenging food matrices. It ensures compliance with stringent safety standards and supports quality control in food processing and regulatory testing.

Future Trends and Possibilities

Potential developments include expanding the approach to other heavy metals, integrating automated sample introduction systems, enhancing throughput with multiplexed autosamplers, and coupling GFAAS with hyphenated techniques for speciation analysis. Further miniaturization and green chemistry approaches may reduce reagent consumption and waste.

Conclusion

The Agilent 280Z GFAAS method with an Omega platform tube delivers robust, high-sensitivity determination of lead in soy sauce. Optimized furnace conditions and streamlined calibration yield reliable results that meet and exceed GB 2762-2017 requirements. Interlaboratory validation confirms the method's precision and suitability for routine food safety monitoring.

Reference

• GB 2762:2017 National Standard for Food Safety – Limits of contaminants in foods.
• Optimizing GFAAS Ashing and Atomizing Temperatures using Surface Response Methodology, Agilent, 5991-9156EN.
• Characteristic Mass in Graphite Furnace Atomic Absorption Spectrometry, Agilent, 5991-9286EN.
• GB 5009.12-2017 National Food Safety Standard – Determination of lead in foods.