Determination of Cadmium in Brown Rice by Flame Atomic Absorption Spectrometry

Importance of Topic

Cadmium is a toxic heavy metal that can accumulate in brown rice, posing significant health risks. With regulatory limits for cadmium in rice recently lowered to 0.4 mg/kg in Japan, accurate and sensitive analytical methods are essential to ensure food safety and regulatory compliance.

Aims and Overview of the Study

This study demonstrates the determination of cadmium in powdered brown rice reference materials (NIES No.10-a and No.10-b) using flame atomic absorption spectrometry (AAS). It compares the performance of the standard flame AAS method with a high-sensitivity approach employing a quartz atom booster above the burner head.

Methodology and Instrumentation

Sample preparation combined acid thermal decomposition with organic solvent extraction following official guidelines.

• Acid decomposition: weigh 10 g sample, add water, nitric acid and heat; add sulfuric acid and additional nitric acid until colorless; dilute to 100 mL.
• Solvent extraction: transfer aliquot to separatory funnel, add potassium sodium tartrate, bromthymol blue indicator; neutralize with ammonia; add sodium sulfate and diethyldithiocarbamate; extract chelated cadmium with methyl isobutyl ketone (MIBK).

Instrumentation:

• Flame AAS system configured at 228.8 nm wavelength, 0.7 nm slit width, 8 mA current, background correction BGC-D2.
• Acetylene–air flame at 0.8 L/min; burner height 9 mm (standard) and 13 mm (with 15 cm quartz atom booster).

Main Results and Discussion

Calibration curves for both methods exhibited excellent linearity (r≈1.000). The atom booster increased absorbance by over twofold compared to the standard flame method. Measured cadmium concentrations for NIES No.10-a and No.10-b were 0.024 mg/kg and 0.31 mg/kg respectively, matching certified reference values for both configurations.

Benefits and Practical Applications of the Method

The enhanced sensitivity provided by the atom booster enables reliable quantification of cadmium at low concentrations, supporting stringent regulatory requirements. This approach is well suited for routine QA/QC analysis in food safety laboratories.

Future Trends and Potential Uses

Future developments may include further automation of sample preparation, integration of alternative extraction techniques (e.g., ultrasonic or microwave-assisted extraction), expansion to other toxic elements such as lead, copper, manganese and nickel, and the design of portable field analysis systems for on-site monitoring.

Conclusion

Incorporating a quartz atom booster into flame AAS significantly improves detection sensitivity for cadmium in brown rice, ensuring compliance with tightened food safety standards. The optimized method delivers accurate, precise and practical performance for routine analytical workflows.

Reference

• Shimadzu Application News No. A277 – Flame Atomic Absorption Spectrometry Using an Atomic Booster
• Shimadzu Application News No. A348 – Measurement of Cadmium in Rice
• Shimadzu Application News No. J87 – Multi Element Simultaneous Determination in Brown Rice by ICP Emission Spectrometry