Feasibility Study for the Determination of Polychlorinated Naphthalenes in Food Samples Using DEXTech Plus/Pure Systems

Significance of the Topic

Polychlorinated naphthalenes (PCNs) are persistent, lipophilic pollutants with toxicological profiles similar to dioxins and certain PCBs. Historically used in technical mixtures as flame retardants, dielectric fluids and preservatives, these compounds pose health risks due to bioaccumulation in the food chain. Monitoring PCNs in food products, especially fats, fish and eggs, is essential for consumer safety and regulatory compliance. Automated multi-method sample preparation enhances laboratory efficiency and supports the expanding scope of persistent organic pollutant (POP) analysis.

Objectives and Study Overview

This feasibility study evaluates an automated cleanup approach using the DEXTech Plus/Pure systems coupled with high-resolution gas chromatography–mass spectrometry (HRGC-HRMS) for the determination of 26 PCN congeners in food oils. The method aims to enable simultaneous quantification of PCNs, polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) in a single workflow.

Methodology and Instrumentation

Sample Preparation and Standards

• Analytes: 26 selected PCN congeners, covering mono- to octa-chlorinated homologues.
• Internal Standards: Eight 13C-labelled PCNs plus 13C PCN 65 as final standard for isotope dilution.
• Matrices: Vegetable oil (blank) and contaminated fish oil samples.
• Volatility Tests: Assessed losses during nitrogen blow-down and rotary evaporation to optimize evaporation steps.

Cleanup Procedures

• DEXTech Methods: Alox Plus Default (Method I) and Alox (Method II) protocols implemented on both DEXTech Plus and Pure platforms.
• Columns: Standard and Universal cleanup columns evaluated for PCN elution efficiency.

Instrumental Analysis

• GC-HRMS: High-resolution magnetic sector MS (resolution 10 000) for quantification.

Instrumentation Used

DEXTech Systems

• DEXTech Plus (P/N 15011)
• DEXTech Pure (P/N 15969)
• DEXTech Heat (P/N 16800)
• DEXTech 16 (P/N 15430)

Cleanup Columns

• Universal column (P/N 19511)
• Smart columns (P/N 19513)
• Alox column (P/N 15433)
• Carbon column (P/N 15424)

Main Results and Discussion

Evaporation Effects

• Nitrogen blow-down and rotary evaporation significantly reduce recoveries of lower-chlorinated PCNs, highlighting the need for controlled evaporation to preserve analytes.

Recovery and Precision

• 13C-labelled PCN recoveries in the target fraction ranged from 34 % to 83 % (intraday) and 38 % to 87 % (interday).
• Native PCN quantification via isotope dilution achieved trueness of 73 %–123 % and relative standard deviations below 11 %.
• Method I on Universal column with final standard addition before evaporation improved average recoveries up to 112 % for highly chlorinated congeners.

Long-Term Performance

• Over two years, varied operators and cleanup conditions yielded consistent native PCN levels (312–320 pg/g fat) and recoveries within 40 %–120 %.
• Simultaneous PCDD/F and PCB analysis in the same extracts produced results within ±2 × standard deviation of established fish oil quality control limits.

Benefits and Practical Applications

The automated DEXTech cleanup enables simultaneous purification of PCNs, PCDD/Fs and PCBs from food fats, reducing manual handling and improving throughput. High-resolution HRMS quantification combined with isotope dilution offers robust accuracy and precision, supporting regulatory monitoring and risk assessment in food safety laboratories.

Future Trends and Applications

Advancements may include expanded multi-analyte panels for emerging POPs, optimized protocols to minimize volatility losses of low-chlorinated congeners, and integration with liquid chromatography–tandem mass spectrometry (LC-MS/MS) for complementary screening. Further automation and miniaturization could enable high-throughput analysis of diverse matrices under tightening regulatory frameworks.

Conclusion

This feasibility study demonstrates that the DEXTech Plus/Pure systems, combined with Alox-based cleanup methods and HRGC-HRMS, provide a reliable, automated solution for concurrent PCN, PCDD/F and PCB analysis in food oils. The approach offers acceptable recoveries, strong precision and the flexibility required for routine POP monitoring.

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