Application of ICP-OES for the simultaneous analysis of nutritional and toxic metals in vegetable oils

Importance of the Topic

Vegetable oils are a staple in global diets, valued for culinary uses and health benefits. Monitoring trace and major elements ensures food safety, as toxic metals such as lead must comply with strict regulatory limits to protect human health.

Objectives and Study Overview

This study aimed to develop and validate a robust ICP-OES method for simultaneous quantitation of nutritional and toxic metals in food-grade vegetable oils, demonstrating sensitivity, accuracy and long-term stability under routine conditions.

Methodology and Instrumentation

Sample Preparation:

• Accurate weighing of 4 g oil samples and five-fold dilution with xylene to a final mass of 20 g
• Use of xylene as diluent in standards, QC, spikes and autosampler rinse

Instrumentation and Software:

• Thermo Scientific iCAP PRO Series ICP-OES Duo equipped with a demountable ceramic D-torch, 1 mm quartz center tube, concentric nebulizer and cyclonic spray chamber
• Plasma conditions: 1250 W RF power, 13.5 L/min coolant gas, 0.25 L/min auxiliary Ar/O₂ gas, 0.35 L/min nebulizer gas
• Data acquisition via Qtegra ISDS software enabling automatic plasma tuning, full-range wavelength scanning and interference-free line selection

Calibration and Quality Control:

• Calibration standards from 0.2 to 1.0 mg/kg for 22 elements, including blank, CCV at 1.0 mg/kg and spike at 0.2 mg/kg
• Yttrium (1 mg/kg) used as internal standard to track instrument stability
• Analysis sequence of ~3 hours with batches of five unknown samples followed by CCV injections for calibration verification

Main Results and Discussion

The method delivered exceptionally low detection limits (MDLs from 0.001 to 0.107 mg/kg) and linearity with R² > 0.9993 in both axial and radial modes. Use of the ceramic D-torch reduced background and improved sensitivity, notably for silicon in xylene. Spike recoveries ranged from 90% to 107% with RSDs below 1% (sodium RSD at 4.5%), while CCV recoveries remained within ±0.8% RSD over the sequence. The internal standard response (yttrium) showed 94–103% recovery relative to initial runs, confirming robustness.

Benefits and Practical Applications of the Method

This rapid and reliable approach enables routine QC laboratories to:

• Comply with regulatory limits for toxic metals in vegetable oils
• Obtain high-quality analytical data with minimal sample preparation
• Leverage flexible viewing modes (axial/radial) and enhanced UV capability for challenging elements

Future Trends and Opportunities

Emerging directions may include:

• Integration of automated sample handling and AI-driven spectral interpretation
• Extension to other complex matrices and multi-matrix screening
• Advances in full-spectrum data processing for trace element profiling
• Development of miniaturized or field-deployable ICP-OES systems

Conclusion

The validated ICP-OES method employing a ceramic D-torch and xylene dilution offers exceptional sensitivity, accuracy and robustness for multi-element analysis in vegetable oils, supporting routine food safety monitoring and compliance requirements.

Reference

1. Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs
2. Japan Ministry of Health, Labor and Welfare official guidelines