Measurement of Trace Heavy Metals in Food with Nutrient Function Claims by Microwave Digestion- Furnace Method

Significance of the Topic

Foods with nutrient function claims may be contaminated by trace heavy metals during production or from raw ingredients. Accurate and sensitive determination of lead, arsenic and cadmium is critical to ensure regulatory compliance and consumer safety.

Objectives and Overview

This study demonstrates a rapid and sensitive approach to quantify trace levels of Pb, As and Cd in a commercial vitamin product. Microwave-assisted digestion is combined with graphite furnace atomic absorption spectrophotometry to achieve detection in the ppb range.

Methodology

Sample Preparation:

• 0.5 g of vitamin material was digested with 6 mL HNO3 and 2 mL H2O2 in a microwave vessel pre-cleaned with dilute nitric acid.
• A five-step microwave program reached 200 °C with a maximum power of 500 W over 30 minutes.
• After cooling, the digest was evaporated, reconstituted in 0.25 mL HNO3 and diluted to 50 mL with ultrapure water.

Used Instrumentation

• Shimadzu AA-7000F Atomic Absorption Spectrophotometer
• Graphite furnace atomizer with autosampler (GFA-7000A / ASC-7000)
• Palladium nitrate as a matrix modifier for As and Cd analyses

Main Results and Discussion

• Calibration curves for Pb, As and Cd showed correlation coefficients ≥ 0.999.
• Limits of quantitation were 0.3 ppb for Pb, 3 ppb for As and 0.05 ppb for Cd.
• All target elements were below LOQ in the sample, corresponding to < 0.03 mg/kg Pb, < 0.3 mg/kg As and < 0.005 mg/kg Cd.
• Spike recovery tests yielded 96–108 % recovery, demonstrating method accuracy and minimal matrix effects.

Benefits and Practical Applications

• Microwave digestion reduces processing time and reagent consumption versus conventional wet or dry methods.
• Graphite furnace AAS achieves high sensitivity at ppb levels.
• The workflow minimizes volatilization losses and environmental impact, suitable for routine quality control in food and supplement analysis.

Future Trends and Opportunities

• Integration with automated sample handling for higher throughput.
• Expansion to multielement and speciation analyses using advanced detectors.
• Further reduction of detection limits to meet evolving regulatory requirements.

Conclusion

The combination of microwave-assisted digestion and graphite furnace AAS provides a fast, reliable and sensitive method for monitoring heavy metals in nutrient supplements. The approach meets stringent regulatory standards and supports routine quality assurance in the food industry.

References

• Standard Tables of Food Composition in Japan – 2015 (Seventh Revised Edition), Analysis Manual.