Speciation of Inorganic Arsenic in Baby Rice Cereals Using HPLC-ICP-MS

Significance of the Topic

Rice is a major dietary source of inorganic arsenic, a human carcinogen linked to cancer, diabetes, and cardiovascular disease. Infants are highly vulnerable due to their low body weight and developing systems. Accurate speciation of arsenic in baby rice cereals is therefore critical for risk assessment, regulatory compliance, and ensuring food safety.

Objectives and Study Overview

The study applied the FDA Elemental Analysis Manual (EAM) Section 4.11 HPLC-ICP-MS method to 31 commercially available baby rice cereals. It aimed to separate and quantify individual arsenic species (As(III), As(V), DMA, MMA) and to determine total arsenic levels, providing data on dietary exposure for infants.

Methodology and Instrumentation

• Sample Preparation: One-gram cereal samples were digested in 0.28 M HNO₃ at 95 °C for 90 min, diluted with water, centrifuged, filtered (0.45 µm), and adjusted to pH 6–8.5.
• HPLC Separation: Anion-exchange chromatography on Hamilton PRP-X100 column (4.1×250 mm, 10 µm) using 10 mM ammonium phosphate buffer (pH 8.25) at 1 mL/min.
• ICP-MS Detection: Agilent 7700x ICP-MS in helium collision mode monitored m/z 75 for As⁺ and m/z 77 for ArCl to eliminate interferences. A post-column internal standard (As(V), 2 ng/g) corrected for signal drift.
• Quality Control: NIST SRM 1568a and 1568 rice flour standards validated method performance. Calibration was linear (R² = 1.00) over 0.25–20 ng/g.

Instrumentation Used

• Agilent 1200 Infinity LC system (degasser, binary pump, autosampler, 10-port valve)
• Shimadzu LC-20AD external pump for internal standard addition
• Agilent 7700x ICP-MS with MicroMist nebulizer and Scott double-pass spray chamber
• Milli-Q water purification system (resistivity > 18 MΩ·cm)

Results and Discussion

The method achieved clear separation of As(III), DMA, MMA, and As(V) with no blank contamination. LODs ranged from 0.9 to 1.8 ng/g and LOQs from 7 to 14 µg/kg. Precision (%RSD) was below 7% for all species and total arsenic. Spike recoveries for inorganic As, DMA, and MMA ranged from 97% to 115%. Total As in cereals ranged from 79.9 to 277 µg/kg (mean 174.4 µg/kg) and inorganic As comprised 23–81% of total (mean 58.2%, iAs 101.4 µg/kg). Mixed grain cereals showed lower levels (mean iAs 62.8 µg/kg). On a per-serving basis, mean iAs was 1.5 µg, below FDA‐reported infant cereal average of 2.7 µg. Mass balances averaged 96.7%.

Benefits and Practical Applications

• Accurate quantification of toxic vs. organic As species supports food safety.
• Method aligns with regulatory protocols for infant food monitoring.
• Certified reference materials ensure robust quality control.
• Approach adaptable to diverse cereal matrices.

Future Trends and Potential Applications

• Advanced column chemistries and gradient elution for faster separations.
• Automated, high-throughput screening in routine surveillance.
• Miniaturized HPLC-ICP-MS systems for field deployment.
• Integration with epidemiological studies on dietary arsenic exposure.
• Standardization of species‐specific regulatory limits.

Conclusion

The validated FDA EAM 4.11 HPLC-ICP-MS method provided high sensitivity, precision, and accuracy for arsenic speciation in baby rice cereals. The data support refined risk assessments and contribute to safer infant diets.

References

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