Analysis of Cadmium in Brown Rice by Flame Atomic Absorption Spectrometr

Importance of the Topic

Cadmium is a toxic metal commonly found in various foodstuffs, with rice being the largest source of dietary exposure in many regions. Regulatory bodies have tightened limits on cadmium levels in rice due to health concerns, yet conventional analytical protocols involve lengthy, hazardous wet ashing and organic solvent extractions. A faster, safer screening method is valuable for laboratories to rapidly identify samples that may exceed legal thresholds.

Goals and Study Overview

This study explores a simplified procedure for quantifying cadmium in brown rice through diluted acid extraction followed by flame atomic absorption spectrometry (FAAS) enhanced with an atom booster. The aim is to assess extraction efficiency, sensitivity gains from the booster, and the method’s suitability for preliminary screening against certified reference material.

Methodology

Brown rice powder (2 g, certified reference material NMIJCRM 7531-a) was shaken for 1 h at room temperature in 20 mL of 1 mol/L nitric or hydrochloric acid, then filtered to obtain the test solution. Calibration curves were constructed by measuring standards within the 0–0.1 mg/L range. Limit of quantification (LOQ) was derived from ten blank measurements and expressed as the concentration corresponding to ten times the standard deviation, converted to a solid-matrix basis.

Used Instrumentation

• Atomic absorption spectrophotometer: Shimadzu AA-7800F
• Flame system: Air–acetylene flame with adjustable burner head
• Atom booster: Quartz tube with staggered vertical slits to increase atom residence time
• Analytical settings: 228.8 nm wavelength, 0.7 nm slit, D2 background correction, 5 s integration, three replicates

Main Results and Discussion

Nitric acid extraction recovered nearly all cadmium, outperforming hydrochloric acid. Incorporating the atom booster enhanced absorbance by approximately 2.5 times compared to the standard flame configuration. Calibration curves showed excellent linearity. LOQ improved from 0.07–0.10 mg/kg without the booster to 0.03–0.04 mg/kg with the booster, well below the regulatory limit of 0.4 mg/kg.

Benefits and Practical Applications

• Rapid diluted-acid extraction reduces preparation time and hazardous waste
• Enhanced sensitivity via atom booster enables detection well below legal thresholds
• Suitable for quick screening in quality control labs before full official method analysis
• Modular AA-7800 series allows system upgrades for additional functions

Future Trends and Potential Uses

Future developments may include flow-injection automation, advanced nano-structured boosters, and integration with chemometric data processing to further improve sensitivity and throughput. Applying similar enhancements to other trace metals (Pb, Cu) could expand routine monitoring in food safety and environmental testing.

Conclusion

The proposed diluted acid extraction combined with flame AA and an atom booster offers a practical, high-sensitivity screening method for cadmium in brown rice. It streamlines sample preparation, significantly lowers LOQ, and provides a reliable tool for preliminary compliance checks alongside established official protocols.

References

1. Food Safety Division, Pharmaceutical and Food Safety Bureau, Ministry of Health, Labour and Welfare, Q&A on Cadmium in Foods, Revised July 2010.
2. Ministry of Health, Labour and Welfare Notification No. 183, April 8, 2010.
3. Japan Food Hygiene Association, Standard Methods of Analysis in Food Safety Regulation.
4. Shimadzu Application News A427.