Agilent ICP-MS Journal (February 2016 – Issue 64)

Importance of Topic

Arsenic exposure through drinking water, food and occupational sources poses significant health risks, including cancer. Inorganic arsenic (iAs) is more toxic than its organic forms, creating a regulatory need for rapid, reliable speciation methods in food and biological fluids. High-throughput approaches are critical for population studies, environmental monitoring and compliance with tightening regulations on dietary arsenic levels.

Aims and Overview

This work presents streamlined ion-exchange chromatography coupled to triple quadrupole ICP-MS (ICP-QQQ) for the fast separation and quantification of key arsenic species in rice flour and human urine. The objective is to reduce runtime and maintain analytical performance, enabling large-scale biomonitoring and food testing under emerging EU and potential U.S. regulations.

Methodology and Instrumentation

Sample Preparation

• Rice flour extracted in 1.8 % HNO₃/3 % H₂O₂ at 80 °C, centrifuged and diluted.
• Urine diluted 5-fold with deionized water.

Chromatography

• Agilent 1260 Infinity Quaternary LC with 50 mm × 4.6 mm PRP-X100 anion exchange column (5 µm).
• Isocratic elution (50 mM NH₄)₂CO₃, 3 % MeOH, 1.5 mL/min for food species.
• Gradient elution for urine: initial 20 %/80 % A/B at 1 mL/min, ramp to 100 % A at 2 mL/min, total cycle 3.5 min.
• Column temperature 35 °C.

ICP-QQQ Conditions

• Agilent 8800 in MS/MS mode with O₂ cell gas.
• Q1 set to m/z 75 to exclude interferences; Q2 monitors AsO⁺ at m/z 91.
• Carrier gas 1.1 L/min; spray chamber rinse at 0.5 rps.
• Integration time 50 ms per channel.

Main Results and Discussion

Isocratic separation of arsenobetaine (AB), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and total iAs (sum of As(III) and As(V)) completed in 1.7 min, with detection limits of 10 ng/L for organic species and 50 ng/L for iAs. Urine method resolved six species, including arsenocholine and As(III), in 3.5 min. Recoveries for certified reference materials (NIST 1568b rice flour, NIST 2669 urine) ranged from 92 % to 110 %. Occasional oxidation of As(III) to As(V) in SRMs was attributed to sample handling rather than the method itself.

Benefits and Practical Applications

• 4–7× faster chromatography compared to conventional methods, boosting sample throughput.
• Low detection limits suitable for regulatory compliance and biomonitoring.
• Minimal changes to existing HPLC and ICP-QQQ hardware; uses standard columns and reagents.
• Applicable to population-scale urine analysis, food safety testing and environmental monitoring.

Future Trends and Opportunities

Further simplification may be achieved by pre-oxidizing As(III) to As(V) for total iAs assays. Advances in column technology or microfluidic formats could push runtimes below 1 min. Integration with automated sample prep and online dilution systems will support large-scale studies. Emerging tandem and high-resolution ICP-MS designs may improve interference removal and sensitivity for novel arsenic species.

Conclusion

The presented ICP-QQQ methods deliver rapid, robust arsenic speciation in food and urine, with high throughput, low limits of detection and excellent accuracy. They address growing analytical demands driven by regulatory changes and large-scale exposure assessments.

Reference

• Jackson B.P., Liba A. Fast ion chromatography-ICP-QQQ for arsenic speciation. J Anal Atom Spectrom. 2015;30(6):1405–7.
• Verdon C.P. et al. Determination of seven arsenic compounds in urine by HPLC-ICP-DRC-MS. Anal Bioanal Chem. 2009;393(3):939–47.