Robust and sensitive multi-element determination in vegetable oil using ICP-OES

Importance of the topic

Vegetable oils are a staple in the global food supply. They naturally contain trace elements but can also accumulate toxic metals during agricultural and extraction processes. Regulatory bodies, including Codex, the EU, and Japan, set stringent limits for contaminants such as lead (<0.1 mg·kg−1). Sensitive, accurate, and robust multi-element analysis is therefore essential for ensuring food safety, quality control, and regulatory compliance in the oil industry.

Objectives and overview of the study

This study evaluates the performance of the Thermo Scientific iCAP PRO Series ICP-OES with a ceramic D-torch for the multi-element determination in food-grade vegetable oil. The goals include achieving low detection limits, reliable quantification of both major and trace elements, and robust long-term operation under challenging organic sample conditions.

Methodology and instrumentation

• Sample preparation: Vegetable oil samples (4.0 g) were diluted to 20 g with xylene and spiked with yttrium (1 mg·kg−1) as an internal standard to correct for instrument drift. Blanks and standards were prepared in pre-cleaned PFA bottles.
• Instrumentation: The iCAP PRO XP ICP-OES Duo system equipped with a ceramic D-torch and an organic spray chamber was used. A concentric nebulizer delivered the sample, and mixed gas (Ar 80%/O2 20%) was added to reduce carbon deposition. Viton tubing was employed for solvent resistance. The system operated with both axial and radial viewing modes and included an enhanced eUV mode for UV-sensitive elements.
• Software and automation: Qtegra ISDS Software managed wavelength selection, data acquisition, and reporting. A Teledyne CETAC ASX-280 autosampler automated the sample introduction workflow.

Main results and discussion

• Linearity and sensitivity: Calibration across 0.1–1.0 mg·kg−1 yielded R2 >0.9993 for all 22 elements. Limits of detection were below 0.01 mg·kg−1, meeting the requirements for analysis of toxic elements in oils.
• Silicon analysis: The ceramic D-torch reduced the background equivalent concentration for Si by tenfold compared to a quartz torch (BEC 0.002 mg·kg−1), with no signal drift observed during long acquisitions.
• Accuracy and precision: Spike recoveries for all elements ranged from 90% to 107%, with RSDs below 1% (Na at 4.5%). Method detection limits, accounting for sample dilution, remained well below regulatory thresholds.
• Robustness: Analysis of 51 samples over 3 hours with periodic calibration checks (n=5) demonstrated QC recoveries within ±0.8%. Internal standard response stayed within 94%–103%, confirming stable performance.

Benefits and practical applications of the method

The optimized ICP-OES method offers:

• High sensitivity for both nutritional and toxic elements in complex organic matrices.
• Reduced maintenance and extended operational uptime due to the ceramic D-torch.
• Flexibility to select optimal viewing modes and wavelength ranges for various analytes.
• Compliance with international regulatory limits for heavy metals in vegetable oil.

Future trends and applications

Advancements may include further enhancements in eUV sensitivity, integration with advanced autosampling systems, and expansion to other fatty food matrices. Continued improvements in software algorithms for interference correction and real-time monitoring will support higher throughput and more stringent quality control requirements.

Conclusion

The Thermo Scientific iCAP PRO XP ICP-OES equipped with a ceramic D-torch enables robust, sensitive, and accurate multi-element analysis of vegetable oils. The method meets regulatory demands, demonstrates excellent precision and accuracy, and offers long-term stability with minimal maintenance. This approach provides a powerful tool for quality assurance and safety monitoring in the food industry.

References

1. Japanese Ministry of Health, Labor and Welfare – Food Element Limits: https://www.e-healthnet.mhlw.go.jp/information/dictionary/food/ye-039.html
2. Food Safety Commission of Japan – Fact Sheets on Silicone Additives: https://www.fsc.go.jp/sonota/factsheets/130617_silicone.pdf