Fast Analysis of Arsenic Species in Infant Rice Cereals using LC-ICP-QQQ

Importance of the Topic

Arsenic contamination in food, particularly in infant rice cereals, poses significant health risks due to the toxicity of inorganic arsenic species. Rapid and reliable speciation methods are essential for routine monitoring, regulatory compliance, and reducing human exposure to this class 1 carcinogen.

Aims and Study Overview

This study aimed to develop and validate a fast, fit-for-purpose method for routine determination of inorganic arsenic (iAs) and two common organic arsenic species (MMA and DMA) in infant rice cereals. Key objectives included:

• Reducing analysis time to under two minutes per sample.
• Achieving low detection limits compatible with proposed regulatory action levels (100 ppb iAs).
• Demonstrating accuracy and reproducibility using certified reference materials and market samples.

Methodology

Sample Preparation:

• Weighed 1 g of rice cereal and extracted arsenic with 10 mL 0.28 M HNO₃ at 95 °C for 90 min.
• Diluted, centrifuged, filtered, and oxidized As(III) to As(V) using H₂O₂ to quantify total iAs as As(V).

Chromatographic Conditions:

• Column: Hamilton PRP-X100, 50 × 2.1 mm, 5 µm.
• Mobile phase: 40 mM ammonium carbonate with 3% v/v methanol, pH 9.0.
• Flow rate: 0.5 mL/min; injection volume: 5 µL; sample at 4 °C.

Used Instrumentation

Analysis was performed on an Agilent 1260 HPLC coupled to an Agilent 8800 Triple Quadrupole ICP-MS. Oxygen served as cell gas in MS/MS mode to eliminate chlorine‐based interferences on m/z 75. An arsenobetaine internal standard was introduced post-column via flow injection.

Main Results and Discussion

Separation and Sensitivity:

• Baseline separation of As(V), MMA, and DMA achieved in under 2 minutes.
• Limits of detection: 0.018–0.026 µg/kg; limits of quantification: 0.175–0.258 µg/kg, corresponding to ≈8–13 µg/kg in rice.

Method Validation:

• Certified reference materials (NIST 1568b, NMIJ 7503a/7532a, ERM BC-211) yielded species recoveries of 93–123% and total As recoveries of 92–112%.
• Z‐scores for all measurements were within regulatory acceptability (±3).

Market Sample Analysis:

• Six infant rice cereals were analyzed in duplicate.
• Four samples fell below the proposed 100 ppb iAs limit; two exceeded it.
• MMA was detectable above LOQ in only two samples; DMA ranged from ≈11–47 µg/kg.

Benefits and Practical Applications of the Method

• Analysis time ten times faster than the current FDA 4.11 method, increasing sample throughput.
• Improved sensitivity and lower detection limits enable compliance with strict action limits.
• Single HPLC-ICP-QQQ setup supports both speciation and total arsenic measurements.
• Applicable for routine QA/QC testing in food industry and regulatory laboratories.

Future Trends and Potential Applications

• Integration with automated sample preparation and data analysis workflows.
• Expansion to other food matrices (e.g., rice products, beverages) and environmental samples.
• Development of single-quadrupole ICP-MS protocols for laboratories without QQQ capability.
• Adoption of stricter regulatory thresholds may drive further methodological refinements.

Conclusion

A rapid HPLC-ICP-QQQ method for arsenic speciation in infant rice cereals has been established, delivering sub-two-minute analyses, robust quantification, and compliance with proposed regulatory limits. Its high throughput and reliable performance make it an effective tool for ensuring food safety.

Reference

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