Analytical Method for Polycyclic Aromatic Hydrocarbons (PAHs) in Yerba Mate Tea Using Modified QuEChERS, Solid Phase Extraction and GC-TOFMS and GC-MS/MS

Significance of the Topic

Yerba mate tea, widely consumed in South America and now gaining global popularity, can contain elevated levels of polycyclic aromatic hydrocarbons (PAHs) due to traditional wood-fire drying processes. Some PAHs are recognized carcinogens, and their presence in mate tea has been linked to increased cancer risk in consumer populations. Rapid, cost-effective analytical methods are essential for routine monitoring of these contaminants to ensure consumer safety and regulatory compliance.

Objectives and Study Overview

This work aimed to develop and validate a streamlined protocol for quantifying both regulated PAH4 (benzo[a]pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene) and PAH8 compounds in yerba mate tea. The goals were to reduce sample preparation time and resource consumption while achieving reliable recoveries and chromatographic resolution of isobaric interferences.

Methodology and Instrumentation

Sample Preparation

• Modified QuEChERS extraction: 1 g powdered dry tea was hydrated in 10 mL water, spiked with analytes, then extracted with 10 mL hexane:acetone (1:1 v/v) and unbuffered QuEChERS salts.
• Solid phase extraction cleanup: Dual exchanges to neat hexane followed by silica SPE cartridges eluted with 30% methylene chloride in hexane.

Chromatography and Detection

• GC-TOFMS: 60 m Rxi-PAH column, hydrogen carrier, splitless injection, electron ionization, mass range 45–550 amu at 5 Hz.
• GC-MS/MS: 40 m Rxi-PAH column, helium carrier, SRM transitions of molecular ions for interference reduction.

Key instrumentation included LECO Pegasus III GC-TOFMS, Thermo TSQ™ 8000 GC-MS/MS, Restek QuEChERS salt kits, and silica SPE cartridges.

Main Results and Discussion

Extraction solvent comparison showed hexane:acetone (1:1) outperformed acetonitrile, yielding 80–140% recoveries across PAHs versus progressively declining recoveries with acetonitrile for higher-molecular-weight analytes. Optimization of SPE elution solvent at 30% methylene chloride balanced recovery and matrix cleanup.
Chromatographic optimizations using a high-phenyl GC phase achieved baseline separation of key isobaric pairs (e.g., chrysene/triphenylene, benzo[b]/[j]/[k]fluoranthenes) within a 35 min run. This resolution prevents overestimation of toxic PAHs.
Recovery studies at 500 ng/g fortification yielded 72–130% recoveries for 30 PAHs, with EFSA PAH4 recoveries of 81–100% and PAH8 recoveries of 81–110%. Comparison of incurred PAH4 levels in six commercial teas by GC-TOFMS and GC-MS/MS agreed within 5–15%, validating both platforms.
Measured concentrations of the sum PAH4 ranged from 190 to 800 ng/g dry tea, far exceeding typical food limits of 1–10 ng/g.

Benefits and Practical Applications

This protocol reduces solvent use, labor, and analysis time compared to exhaustive techniques (e.g., pressurized fluid extraction, gel permeation chromatography). The combination of modified QuEChERS and SPE cleanup with MS-based detection delivers high selectivity and sensitivity for routine quality control in food safety laboratories.

Future Trends and Potential Uses

Further miniaturization of sample preparation and adoption of high-resolution mass spectrometry could enable multi-class contaminant screening in complex botanicals. Automated QuEChERS workflows and online SPE-GC-MS interfaces may improve throughput. Emerging regulations may extend monitoring to additional emerging PAHs and derivative compounds.

Conclusion

The developed analytical method for PAHs in yerba mate tea offers rapid extraction, efficient cleanup, and robust separation of isobaric interferences. Both GC-TOFMS and GC-MS/MS deliver reliable quantitation of regulated PAH4 and PAH8 marker compounds, facilitating accurate exposure assessment and supporting food safety compliance.

Reference

• Kowalski J, Rigdon A, Cochran J. Analytical Method for Polycyclic Aromatic Hydrocarbons in Yerba Mate Tea Using Modified QuEChERS, Solid Phase Extraction and GC-TOFMS and GC-MS/MS. Restek Application Note FFAN2086-UNV; 2015.
• EFSA Panel on Contaminants in the Food Chain. Scientific Opinion on Polycyclic Aromatic Hydrocarbons in Food. EFSA Journal. 2008;724:1–114.
• Anastassiades M, Lehotay SJ, Stajnbaher D, Schenck FJ. Fast and Easy Multiresidue Method Employing Acetonitrile Extraction/Partitioning and Dispersive Solid-Phase Extraction for Determination of Pesticide Residues in Produce. J AOAC Int. 2003;86(2):412–31.