Determination of Metal Elements in Edible Oils Using ICP-MS

Significance of the Topic

Edible oils are a dietary staple worldwide, but trace and heavy metals present in these oils can pose risks to food safety and oil quality. Regulatory standards such as the Codex General Standard for Contaminants and Toxins in Food and Feed mandate strict limits on elements like arsenic and lead. Moreover, transition metals such as copper, iron, and manganese accelerate lipid oxidation, degrading oil quality during storage and processing.

Study Objectives and Overview

This application study aimed to evaluate a streamlined procedure for quantifying 25 metal elements in various edible oils by directly diluting samples with an organic solvent and analyzing them using an ICPMS-2050 equipped with an organic solvent injection system. Key goals included:

• Validating the accuracy and sensitivity of the method against Codex limits.
• Demonstrating simplified sample preparation without acid digestion.
• Assessing instrument performance, calibration linearity, and spike recoveries.

Methodology and Instrumentation

Sample Preparation and Calibration

• Approximately 0.4 g of vegetable, rice, or olive oil was weighed and diluted tenfold (w/w) with PremiSolv organic diluent.
• Oil-based multi-element and single-element standards were prepared across six calibration levels (0 to 100 µg/kg for most elements, higher for P and alkyl mercury).
• Internal standards (Be, Sc, Y, In, Bi) were introduced in-line via solvent-resistant peristaltic pump tubing.

Instrumentation and Analytical Conditions

• ICPMS-2050 with organic solvent torch, platinum sampling cone, nickel skimmer cone.
• Organic Solvent Injection System and AS-20 autosampler with organic-solvent rinse station.
• Ar plasma gas (20 L/min), auxiliary gas (0.5 L/min), carrier gas (0.6 L/min), and Ar-O₂ mixed gas (70 % Ar, 30 % O₂ at 0.35 L/min) to prevent carbon deposition.
• Collision/reaction cell modes (He at 6 mL/min or H₂ at 7 mL/min) to remove carbon-based polyatomic interferences.

Results and Discussion

Interference Removal and Sensitivity

• Collision and reaction modes effectively suppressed polyatomic interferences such as 12C12C⁺ on 24Mg and 40Ar12C⁺ on 52Cr, lowering background equivalent concentrations from 1000 µg/kg (No Gas) to <0.1 µg/kg.
• Calibration curves remained linear across the full concentration range for all 25 elements.

Detection Limits and Accuracy

• Instrument detection limits (IDLs) in organic solvent ranged from 0.006 µg/kg (Hg) to 3 µg/kg (P), corresponding to oil detection limits of 0.06 to 1000 µg/kg after tenfold dilution.
• Limits for arsenic and lead were well below the Codex limit of 100 µg/kg.

Spike Recoveries

• Spike recovery tests (10 µg/kg for most elements) yielded recoveries between 87 % and 120 %, demonstrating method accuracy in vegetable, rice, and olive oil matrices.

Practical Benefits and Applications

This approach offers several advantages for routine oil analysis in quality control and research laboratories:

• Avoidance of acid digestion reduces risks of analyte loss through volatilization or contamination.
• Direct dilution with organic solvent simplifies workflow and increases sample throughput.
• In-line addition of internal standards via solvent-resistant tubing minimizes manual handling and potential errors.

Future Trends and Applications

Continued advancements may include:

• Automation of organic solvent dilution and direct injection for high-throughput screening.
• Extension to other lipid-rich matrices such as cosmetic oils or biodiesel.
• Development of green solvents and microextraction techniques to further reduce solvent usage.
• Integration with advanced collision/reaction cell chemistries to broaden analyte coverage and lower detection limits.

Conclusion

The combination of simple organic solvent dilution and the ICPMS-2050 with an organic solvent injection system provides a robust, accurate, and high-throughput solution for multi-element analysis in edible oils. This method meets regulatory requirements, minimizes sample preparation complexity, and delivers reliable quantification down to trace and ultra-trace levels.

Reference

Codex General Standard for Contaminants and Toxins in Food and Feed (CODEX STAN 193-1995)