Direct Measurement of Trace Metals in Edible Oils by 7500cx ICP-MS with Octopole Reaction System

Significance of the topic

Edible oils are widely used in cooking, food processing, and even as renewable biofuels. Beyond their nutritional and culinary roles, trace metals in these oils can affect safety, flavor stability, and shelf life. Monitoring ultratrace elements helps to ensure food quality, detect contamination sources, and prevent autoxidation accelerated by transition metals.

Study objectives and overview

This work demonstrates a straightforward, digestion-free approach for determining trace and ultratrace metals in edible oils using an Agilent 7500cx ICP-MS equipped with an Octopole Reaction System (ORS). Seed, olive, and nut oils were analyzed after a simple three-fold dilution in kerosene. A recovery test on rapeseed oil assessed method accuracy.

Methodology and instrumentation

Samples and standards were prepared by weighing high-concentration metal-organic oil standards and diluting them with kerosene. Internal standards (Li, In, Bi) compensated for viscosity effects. The Agilent 7500cx ICP-MS ORS cell operated in helium collision mode and hydrogen reaction mode to remove polyatomic interferences (e.g., ArC, ArO, ArN) and major matrix effects. Oxygen addition to the plasma prevented carbon buildup on the interface. Key operating parameters included 1550 W forward power, 15 L/min plasma gas flow, 0.9 L/min carrier gas, and specific He and H₂ cell gas flows.

Main results and discussion

Detection limits and background equivalent concentrations ranged from low µg/kg (ppb) to ng/kg (ppt) for all elements. Reaction mode reduced the 40Ar¹²C interference on ⁵²Cr from >80 ppb to <0.08 ppb BEC. Collision mode lowered ³⁸Ar¹⁷O and ⁴⁰Ar¹⁵N interferences on ⁵⁵Mn to 0.053 ppb BEC. Recoveries for spiked rapeseed oil varied from 93.7% (Ag) to 107.1% (Sn). Nut oils exhibited higher elemental concentrations than seed or olive oils, reflecting plant uptake differences. An 8.5-hour stability test on spiked rapeseed oil showed precision around 2% RSD (4% for Na due to slight contamination), demonstrating suitability for routine analysis.

Benefits and practical applications

• Minimal sample preparation without acid digestion or aqueous extraction.
• High sensitivity and selectivity for interfered elements using ORS.
• Ppt-level detection limits enable monitoring of toxic trace metals.
• Reduced analysis time and lower risk of contamination or analyte loss.
• Applicability to quality control in food safety labs and industrial settings.

Future trends and applications

Direct oil analysis by collision/reaction cell ICP-MS can expand to biodiesel characterization, routine monitoring of low-level elements such as sulfur and phosphorus, and high-throughput screening. Automation of dilution and sample introduction could further increase productivity. Advances in cell gas chemistries may improve interference removal for emerging analytes.

Conclusion

The direct measurement protocol using a 7500cx ICP-MS with ORS provides a robust, sensitive, and selective method for trace metal analysis in edible oils. The simplicity of dilution preparation, combined with effective interference suppression, enables reliable routine testing with ppt-level detection and excellent accuracy.

References

1. Agilent Technologies. Direct Elemental Analysis of Biodiesel by 7500cx ICP-MS with ORS. Publication 5989-7649EN, April 2008.
2. Choe, E., Min, D. Mechanisms and Factors for Edible Oil Oxidation. Comprehensive Reviews in Food Science and Food Safety, 5, 169–186 (2006).