Accurate and Sensitive Analysis of Arsenic and Selenium in Foods

Significance of the Topic

Contamination of food and beverages by toxic elements such as inorganic arsenic (As) poses severe health risks and is subject to strict regulatory limits by agencies like the U.S. FDA and WHO. Conversely, selenium (Se) is an essential micronutrient that may be deficient in certain soils, requiring precise quantification to assess dietary adequacy. Accurate measurement of trace levels of As and Se in complex food matrices is vital to avoid false compliance, unnecessary product rejections, or misinterpretation of nutrient content.

Objectives and Study Overview

This work investigates the capability of the Agilent 8800 Triple Quadrupole ICP-QQQ operated in MS/MS mass-shift mode with O2/H2 reaction gas to eliminate doubly charged rare earth element (REE) interferences during As and Se analysis. Two NIST standard reference materials, SRM 1547 (Peach Leaves) and SRM 1515 (Apple Leaves), containing low µg/kg levels of As and Se alongside mg/kg levels of REEs, were analyzed. Results were benchmarked against single quadrupole ICP-MS methods using helium and hydrogen collision/reaction modes, including the application of mathematical correction equations.

Methodology

Sample Preparation

• Triplicate microwave-assisted acid digestion of 0.25 g plant material in 9:1 HNO3:HCl at 200 °C.
• Dilution to 25 g final weight with the addition of 5% butanol in the internal standard mix.

Interference Control

• Single quadrupole ICP-MS in He collision mode and H2 reaction mode, with and without mathematical corrections for REE++ overlaps.
• Triple quadrupole ICP-QQQ in MS/MS mass-shift mode, shifting As to AsO+ (m/z 91) and Se to SeO+ (m/z 94) using O2/H2 gas.

Calibration was performed with NIST-traceable standards and second-source checks, requiring 95% confidence intervals to overlap certified ranges.

Used Instrumentation

• Agilent 7700x ICP-MS with octopole collision/reaction cell in He and H2 modes.
• Agilent 8800 Triple Quadrupole ICP-QQQ with concentric nebulizer, Peltier-cooled double-pass spray chamber, and CRC in MS/MS mass-shift mode using 35% O2/65% H2.

Main Results and Discussion

Single quadrupole ICP-MS in He and H2 modes produced As and Se results far above certified values due to unresolved doubly charged REE interferences, even after mathematical corrections, leading to high relative standard deviations in low-level SRMs. In contrast, the ICP-QQQ MS/MS mass-shift method delivered uncorrected As and Se concentrations within the certified ranges for both SRMs, even when spiked with 1 mg/L Zr and Mo. The method achieved 10-fold lower detection limits and eliminated potential overlaps from 91Mo+ and 94Zr+ by rejecting unwanted ions at Q1.

Benefits and Practical Applications

• Reliable removal of both polyatomic and doubly charged REE interferences without extensive post-acquisition corrections.
• Enhanced accuracy and precision at trace levels, reducing false positives/negatives in food safety testing.
• Lower detection limits suitable for regulatory compliance and nutrient assessment in complex matrices.

Future Trends and Opportunities

As the presence of REEs in agricultural products becomes better understood, routine monitoring of REE signals at m/z 150–156 can flag samples prone to interference. The MS/MS mass-shift approach may be extended to other challenging analytes and matrices, and further developments in reaction cell chemistries could improve sensitivity and selectivity. Integration with high-throughput sample preparation and automated workflows will support large-scale food safety and nutritional studies.

Conclusion

The Agilent 8800 Triple Quadrupole ICP-QQQ in MS/MS mass-shift mode with O2/H2 reaction gas offers a robust, accurate, and sensitive solution for trace arsenic and selenium analysis in food matrices containing high levels of doubly charged REEs. By shifting analyte ions to oxide forms and rejecting interferences at the first quadrupole, the method delivers certified-range results without correction equations, supporting regulatory compliance and nutritional assessment.

References

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• U.S. FDA. Guidance for Industry: Arsenic in Apple Juice—Action Level, 2013.
• Anon. FDA sets limit for arsenic in apple juice. Chem. Eng. News 91, 21 (2013).
• FAO/WHO. Report of the Eighth Session of the Codex Committee on Contaminants in Foods, CL 2014/11-CF, 2014.
• Sucharova J. Optimisation of DRC ICP-MS for determining selenium in plants. J. Anal. At. Spectrom. 26, 1756–1762 (2011).
• Wang R-Y et al. Speciation analysis of arsenic and selenium compounds by IC-ICP-DRC-MS. Anal. Chim. Acta 590, 239–254 (2007).
• FDA Elemental Analysis Manual for Food and Related Products, Ver. 1.0, 4.7 ICP-MS Multi-element in Food, 2013.
• Harrington CF et al. Removal of the gadolinium interference from selenium measurement in human serum by Q-ICP-MS. Ann. Clin. Biochem. 51(3), 386–391 (2014).
• Sugiyama N. Accurate selenium measurement using isotope dilution with the 8800 Triple Quadrupole ICP-MS in MS/MS mode. Agilent Technologies App. Note 5991-0259EN, 2012.