Arsenic Speciation in Rice and Rice Products using LC-ICP-MS: A Sensitive and Reliable Approach by Shimadzu

Importance of the Topic

Arsenic exposure through rice and rice‐based foods is a significant health concern due to the element’s toxicity and carcinogenic potential. Inorganic arsenic species—arsenite (As(III)) and arsenate (As(V))—pose the greatest risk, while organic forms such as monomethyl arsenate (MMA) and dimethyl arsenate (DMA) are comparatively less harmful. Accurate speciation is essential for regulatory compliance and risk assessment, especially in regions with strict maximum residue limits for inorganic arsenic in rice products.

Objectives and Overview of the Study

This work demonstrates a sensitive, reliable approach for arsenic speciation in rice and related products using Shimadzu’s LC-ICP-MS-2050 LF system coupled with a Nexera inert liquid chromatograph. The primary goals were to optimize extraction and chromatographic separation, validate method performance, and quantify inorganic and organic arsenic species in various rice matrices.

Methods and Instrumentation

Sample Preparation and Extraction:

• Approximately 0.5 g milled rice or rice‐based product is mixed with 2 mL 0.15 M HNO₃.
• Mixture is vortexed, heated at 120 °C for 2 h, diluted with 8 mL water, and centrifuged.
• Supernatant is filtered (0.22 µm) and further diluted tenfold with 0.15 M HNO₃.

Chromatography and Detection Parameters:

• Column: Pentafluorophenyl, 250 mm × 4.6 mm, 5 µm.
• Mobile Phase: 0.1% formic acid with 1% methanol and 0.025% ion-pair reagent.
• Flow Rate: 0.75 mL/min; Column Temp.: 40 °C; Injection: 10 µL.
• ICP-MS: Shimadzu ICPMS-2050 LF with mini-torch, nickel skimmer cone, He cell gas, plasma gas flow 9 L/min.
• Calibration Range: 0.2–20 µg/L, seven-point external calibration with 1/x weighting.

Main Results and Discussion

Calibration curves for As(III) and As(V) showed linearity across the working range, meeting AOAC accuracy criteria (80–120%). Method recoveries for spiked inorganic arsenic ranged from 77.8% to 119.8%. Duplicate analyses of 22 samples, including white and brown rice, rice crackers, cakes, cereals, and sake, demonstrated good repeatability. In many rice products, inorganic arsenic was detected at levels consistent with regulatory limits, while organic species were present at lower concentrations.

Benefits and Practical Applications

The described approach offers:

• High sensitivity and selectivity for arsenic species at trace levels.
• Robust extraction ensuring consistent recoveries across diverse matrices.
• Streamlined method package requiring minimal user optimization.
• Compliance with international regulatory guidelines for inorganic arsenic in food.

Future Trends and Opportunities

Emerging directions include:

• Automation of sample preparation to increase throughput.
• Integration with emerging mass spectrometric detectors for lower detection limits.
• Extension of speciation protocols to other food and environmental matrices.
• Development of portable on-site analysis systems for rapid screening.

Conclusion

The LC-ICP-MS-2050 LF method provides a sensitive, accurate, and user-friendly solution for arsenic speciation in rice-based products, supporting regulatory compliance and consumer safety. Its robust performance across a variety of sample types underscores its value for analytical laboratories in food quality control and research.

Reference

• Nishimura T, Hamano-Nagaoka M, Sakakibara N, Abe T, Maekawa Y, Maitani T. Food Hygiene and Safety Science. 51 (2010) 178.