Sensitive and Rapid Analysis of Inorganic Arsenic in Food and Animal Feed Samples Using LC-ICP-MS

Significance of the topic

Inorganic arsenic (iAs) is one of the most toxic forms of arsenic and is therefore subject to regulatory control in food and animal feed. Reliable speciation and quantification of iAs—separating it from less toxic organic arsenic species and from polyatomic interferences such as 40Ar35Cl—is essential for food safety, regulatory compliance, and public health. Fast, sensitive, and matrix-robust analytical workflows are needed to meet diverse sample types and increasingly stringent limits (including recent EU and US regulations).

Objectives and overview of the study

This application study evaluated an LC-ICP-MS workflow (Shimadzu Nexera XS inert coupled to ICPMS-2040/2050) for sensitive and rapid quantification of inorganic arsenic across 14 food and animal feed matrices. The objectives were to: confirm complete oxidation of As(III) to As(V) during sample pretreatment; demonstrate chromatographic separation of iAs from organic arsenic species and chloride-derived 40Ar35Cl interference; establish method sensitivity and LODs across matrices; and validate accuracy using spike-recovery tests and certified reference materials (CRMs) in accordance with EN 16802:2016 and EN 17374:2020.

Methodology

• Sample set: 14 matrices including baby foods (rice cereal, apple jelly, strained corn, infant formula), seafood (sea bream, tuna, squid), ham, orange juice, Japanese sake, animal feed, and three CRMs (brown rice NMIJ 7532-a, NMIJ 7533-a; hijiki NMIJ 7405-b).
• Pretreatment: Solid samples (~0.5 g; animal feed ~0.2 g) extracted with Extraction Solution 1 (0.1 M HNO3, 3% v/v H2O2), liquids mixed 1:1 with Extraction Solution 2 (0.2 M HNO3, 6% v/v H2O2). Extraction by heating at ≈90 °C for 60 min, centrifugation, 0.45 µm PTFE filtration. Spiked samples prepared to evaluate recovery. Selective post-extraction dilution applied to reduce matrix effects (e.g., hijiki 200×, some samples 2–10×).
• Oxidation: The protocol intentionally oxidizes As(III) to As(V) so total inorganic As is measured as As(V); oxidation was verified using As(III) standards subjected to the same pretreatment.
• Calibration and QC: Calibration standards (As species except As(III)) prepared at 0.1–20 µg/L. Internal standard: Ga at 0.5 mg/L (online addition). Chloride interference check solution: NaCl at 100 mg/L Cl.

Used instrumentation

• Chromatography: Nexera XS inert HPLC with HAMILTON PRP-X100 anion-exchange column (10 µm, 250 × 4.1 mm). Mobile phase: 100 mM ammonium carbonate + 3% v/v methanol + 400 mg/L sodium sulfate, pH ≈9.3. Flow 1.2 mL/min, column 30 °C, injection 50 µL, runtime 6.5 min/sample.
• Mass spectrometry: Shimadzu ICPMS-2040/2050. Nebulizer: DC04; torch: mini-torch (reduced Ar consumption); cooled cyclone spray chamber; Ni sampling and skimmer cones; helium collision mode (He cell gas at 3.0 mL/min) to remove 40Ar35Cl interference. RF power 1.20 kW.
• Software: LabSolutions ICPMS TRM controlled HPLC and ICP-MS for integrated injection, acquisition and data analysis.

Main results and discussion

• Chromatographic separation: iAs (As(V)) was baseline-separated from the organic arsenic species monitored (AsC, AsB, DMA, MMA) and from the chloride peak; full iAs separation achieved within a 6.5‑minute run.
• Oxidation confirmation: As(III) standard treated by the extraction procedure eluted at the same retention time as As(V) and quantified near the expected concentration (5 µg/L standard measured as 4.83 µg/L), confirming effective oxidation and suitability to quantify total iAs as As(V).
• Cl interference: Chloride elution was chromatographically resolved from iAs; additionally, He collision mode successfully suppressed 40Ar35Cl contributions at m/z 75 at the iAs retention time.
• Matrix effects: Some liquid matrices (notably orange juice) caused retention time shifts when analyzed without post-filtration dilution; a 5× post-filtration dilution (total 10×) mitigated these shifts. Japanese sake showed negligible shift under similar treatment.
• Sensitivity and LODs: Analytical LOD in solution was determined from 10 replicate measurements of the 0.1 µg/L standard (3× SD). Converted sample LODs depended on dilution factors; typical LODs in many solid samples were ≈0.0004 mg/kg, with lower LODs achieved in some liquids (e.g., Japanese sake 0.00004 mg/L). These LODs are sufficient to meet strict regulatory thresholds such as the Baby Food Safety Act limit of 0.01 mg/kg.
• Accuracy and robustness: Spike-recovery tests across 11 non-CRM samples returned recoveries between 96% and 113%, demonstrating method accuracy across diverse matrices. CRMs (brown rice NMIJ 7532-a, NMIJ 7533-a and hijiki NMIJ 7405-b) were quantified within their certified ranges (brown rice results ~0.298 and 0.530 mg/kg; hijiki ~24.7 mg/kg), confirming method validity.
• Representative quantitative findings: Rice cereal had elevated iAs (0.0864 mg/kg). Many other food samples yielded iAs below detection limits; animal feed showed measurable iAs consistent with grain-derived origin (~0.013 mg/kg in the tested sample).

Benefits and practical applications of the method

• High throughput: short 6.5-minute cycle time enables rapid screening of many samples with reduced per-sample time compared to longer chromatographic methods.
• High sensitivity: low LODs allow compliance monitoring even for stringent regulatory criteria (e.g., baby food limits).
• Robust across matrices: validated for a wide variety of foodstuffs and animal feed, including matrices with large organic arsenic loads (seafood) and high chloride content.
• Cost and resource efficiency: the mini-torch reduces argon consumption by roughly one-third versus conventional torches, lowering running costs for continuous LC-ICP-MS operations.
• Regulatory alignment: method follows EN 16802:2016 and EN 17374:2020 guidance for inorganic arsenic determination, supporting compliance testing workflows.

Future trends and potential applications

• Broader species coverage: expansion of chromatographic methods to routinely separate all common arsenic species (AsC, AsB, DMA, MMA, As(III), As(V)) in a single run would benefit comprehensive speciation studies; this study focused on iAs-optimized pretreatment and separation.
• Automation and sample throughput: automated dilution and autosampler functions could further enhance throughput and reduce manual handling for high-volume testing labs.
• Cost optimization: wider adoption of reduced‑consumption torches and optimized gas flows will make routine LC-ICP-MS speciation more affordable.
• Method transfer and harmonization: as regulatory limits evolve (e.g., new EU seafood limits), standardized, validated LC-ICP-MS protocols will be critical for inter-laboratory comparability and enforcement testing.
• Complementary approaches: coupling with alternative sample cleanup or enrichment techniques (e.g., limits of detection improvements, matrix-specific cleanup) may extend applicability to even more challenging matrices.

Conclusion

The described LC-ICP-MS workflow (anion-exchange HPLC with ICPMS-2040/2050) provides a sensitive, rapid, and robust approach for quantifying total inorganic arsenic across diverse food and animal feed matrices. Effective oxidation of As(III) to As(V), chromatographic separation from organic arsenic and chloride peaks, helium collision-cell removal of 40Ar35Cl, low detection limits, strong spike recoveries (96–113%), and accurate CRM results demonstrate suitability for regulatory monitoring and routine laboratory application. The short runtime and reduced argon consumption further support efficient high-throughput testing.

References

1. COMMISSION REGULATION (EU) 2023/915 of 25 April 2023 on maximum levels for certain contaminants in food and repealing Regulation (EC) No 1881/2006.
2. DIRECTIVE 2002/32/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 7 May 2002.
3. Commission Regulation (EU) 2025/1891 of 17 September 2025 amending Regulation (EU) 2023/915 as regards maximum levels of inorganic arsenic in fish and other seafood.
4. US House of Representatives, The Baby Food Safety Act of 2021.
5. EN 16802:2016: Determination of inorganic arsenic in foodstuffs of marine and plant origin by anion-exchange HPLC-ICP-MS.
6. EN 17374:2020: Determination of inorganic arsenic in animal feed by anion-exchange HPLC-ICP-MS.
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