Quantitation of Toxic Tire Degradant 6PPD-Quinone in Surface Water

Importance of the Topic

Quantifying 6PPD-quinone in surface water is critical due to its high toxicity to juvenile coho salmon and other aquatic organisms. As a transformation product of the tire antioxidant 6PPD, this compound has been detected in urban runoff and poses ecological risks at sub-microgram-per-liter levels. Reliable, sensitive, and rapid analysis methods are essential for environmental monitoring and risk assessment.

Objectives and Study Overview

This study presents a streamlined analytical approach using direct injection liquid chromatography coupled to triple quadrupole mass spectrometry (LC/TQ) for the quantitation of 6PPD-quinone in surface water. Key goals include minimizing sample preparation, achieving low reporting limits, and validating method performance in real-world environmental samples.

Used Instrumentation

• Liquid Chromatograph: Agilent 1290 Infinity II with multisampler (G7167B), high-speed pump (G7120A), and multicolumn thermostat (G7116B).
• Analytical Column: Agilent InfinityLab Poroshell 120 EC-C18, 2.1 × 50 mm, 1.9 μm (p/n 699675-902).
• Mass Spectrometer: Agilent 6470 triple quadrupole LC/MS with JetStream ESI source (G6470B).
• Software: MassHunter Acquisition 10.1, MassHunter Quantitative Analysis 10.1, MassHunter Qualitative Analysis 10.0, MassHunter Optimizer.

Methodology

Sample Preparation:

• Surface water samples centrifuged (5 min, 13 000 rpm) and 1 mL directly injected.
• Internal standard D5-6PPD-quinone spiked to 5 ng/mL.
• Calibration standards from 0.01 to 50 ng/mL prepared by serial dilution; high calibrator 50 ng/mL in water, diluted for lower levels.

LC Conditions:

• Mobile Phase A: 1 mM ammonium fluoride in water; Phase B: acetonitrile.
• Gradient: 30% B at 0.0 min, ramp to 70% B at 4.7 min, 100% B at 4.8 min; stop at 5.7 min; post time 1.5 min.
• Flow Rate: 0.6 mL/min; Column Temperature: 40 °C; Injection Volume: 5 μL.

MS Detection:

• Electrospray ionization in positive mode; MRM transitions optimized for precursor 299.2→ fragments 241.1, 215.1, 187.1 m/z; ISTD at 304.2→246.1, 220.1, 192.1 m/z.
• Source parameters: gas temp 300 °C, sheath gas temp 375 °C, gas flow 10 L/min, sheath gas flow 11 L/min, nebulizer 40 psi, capillary voltage 2 500 V.

Key Results and Discussion

The method demonstrated a linear calibration range of 0.01–50 ng/mL (quadratic fit, 1/x weighting) with R² > 0.999. Accuracy (recovery) was 113.5% in HPLC water and 112.6% in stream water. Precision (%RSD) at 5 ng/mL was 3% for water and 1% for stream samples. The minimum reporting limit (LCMRL) was 0.023 ng/mL, well below ecological effect levels. Stability tests over 67 hours and 17 repeated injections showed consistent retention times and signal intensity. Analysis of field samples revealed 6PPD-quinone at 0.06 ng/mL in residential runoff and 0.27 ng/mL in a parking lot puddle, confirming method applicability.

Benefits and Practical Applications

The direct-injection LC/TQ approach offers rapid turnaround (under 8 minutes per sample), minimal sample handling, and high sensitivity. This facilitates high-throughput monitoring of 6PPD-quinone in diverse environmental matrices, supporting regulatory compliance and ecological risk assessments.

Future Trends and Opportunities

Expanding this methodology to include other tire-derived contaminants and transformation products could broaden environmental surveillance. Integration with automated sampling and data processing platforms may enhance throughput. Ongoing studies on the ecotoxicological impacts of 6PPD-quinone will drive method adaptation for emerging monitoring needs.

Conclusion

A robust, sensitive, and efficient LC/TQ method for direct quantitation of 6PPD-quinone in surface water was established and validated. The approach enables detection at sub-nanogram levels with excellent precision, accuracy, and stability, making it a valuable tool for environmental monitoring of toxic tire degradants.

Reference

• Tian Z et al. A Ubiquitous Tire Rubber–Derived Chemical Induces Acute Mortality in Coho Salmon. Science 2021, 371(6525), 185–189.
• PBT Working Group. Summary Fact Sheet: N-1,3-Dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD). ECB.