Measurement of Cadmium (Cd) and Lead (Pb) in Food Additives by Electrothermal Atomic Absorption Spectrometry (ETAAS)

Significance of the Topic

Accurate determination of trace heavy metals such as cadmium and lead in food additives is critical for consumer safety and regulatory compliance. Electrothermal atomic absorption spectrometry (ETAAS) offers high sensitivity and low detection limits, making it an attractive alternative to traditional colorimetric and flame methods. This application demonstrates how ETAAS can streamline purity testing of functional food ingredients.

Aims and Overview of the Study

The primary goal was to quantify cadmium and lead in β-cyclodextrin, a widely used cyclic oligosaccharide in food, pharmaceutical, and cosmetic products. The study compared ETAAS performance against existing methods and assessed the lower limits of quantitation, recovery, and matrix effects under high-acid conditions.

Methodology and Used Instrumentation

Sample Preparation

• Approximately 0.5 g of β-cyclodextrin was digested in a microwave reactor (Milestone ETHOS One).
• Digestion used 8 mL nitric acid with a small volume of water; final volume was adjusted to 50 mL after cooling.
• Spike recovery tests at 0.05 μg/g Cd and 0.5 μg/g Pb validated the pretreatment.

ETAAS Analysis Conditions

• Instrument: Shimadzu AA-7000 atomic absorption spectrophotometer with electrothermal (graphite furnace) capability.
• Platform-type graphite tubes resistant to strong acid matrices.
• Matrix modifier: 5 μL of 50 mg/L palladium nitrate for both elements.
• Wavelengths: Cd at 228.8 nm, Pb at 283.3 nm; slit width 0.7 nm; background correction: D2 lamp.
• Temperature program: ashing at 700 °C (Cd) or 800 °C (Pb); atomization at 2200 °C.
• Calibration ranges: 0.2–1.0 ppb for Cd; 2.5–10 ppb for Pb.

Main Results and Discussion

Neither Cd nor Pb was detected in the unspiked β-cyclodextrin sample. The quantitation limits, based on 0.01 Abs, were determined as 0.003 μg/g for Cd and 0.07 μg/g for Pb. Recovery experiments yielded values close to 100%, confirming method accuracy. Sensitivity tests showed stable absorbance up to 20% nitric acid, illustrating the robustness of the platform tube against matrix acidity. Calibration curves exhibited excellent linearity across the tested ranges.

Benefits and Practical Applications of the Method

• Significantly improved detection limits compared to flame AAS, enabling trace-level analysis.
• Rapid and closed-vessel microwave digestion reduces contamination risk and sample handling time.
• Platform tubes ensure consistent performance in high-acid matrices, enhancing repeatability.
• Dual-use ETAAS/flame instruments can accommodate diverse analytical needs.

Future Trends and Potential Applications

Advances in furnace tube materials and matrix modifiers may further improve sensitivity and reduce interferences. Integration with automated sample preparation and high-throughput autosamplers will expand ETAAS usage in quality control for food, pharmaceuticals, and environmental monitoring. Combination with speciation techniques could offer deeper insights into metal bioavailability and toxicity.

Conclusion

Electrothermal AAS combined with microwave digestion provides a reliable, sensitive, and efficient approach for quantifying cadmium and lead in food-grade β-cyclodextrin. The method meets stringent regulatory limits and offers practical advantages over conventional testing procedures.

Reference

Shimadzu Application News No. A469, "Measurement of Cadmium (Cd) and Lead (Pb) in Food Additives by Electrothermal Atomic Absorption Spectrometry (ETAAS)," 2013.