Testing LC-MS System Robustness with Automated Sample Cleanup Using Red Wine as a Matrix

Significance of the Topic

Monitoring ultra-trace levels of pesticides and fungicides in food and environmental samples is essential to ensure compliance with global regulations and to protect public health. Traditional sample preparation methods are time-consuming and can limit throughput.

Study Objectives and Overview

The aim of this study is to evaluate the robustness and performance of an online automated sample cleanup and preconcentration workflow using a red wine matrix spiked with multiple pesticides and fungicides. The workflow integrates large-volume injection, online cleanup, and LC-MS/MS detection in a single sequence.

Instrumentation

• Thermo Scientific EQuan environmental quantitation system including a TSQ Quantum Ultra triple quadrupole mass spectrometer, Surveyor HPLC pumps, and a CTC autosampler
• Hypersil GOLD preconcentration column (20×2.1 mm, 12 μm) and analytical column (50×2.1 mm, 3 μm)
• HTC PAL autosampler and LCQUAN control software

Methodology

• Sample Preparation: Red Burgundy wine spiked at 500 pg/mL with nine herbicides and six fungicides, no offline treatment prior to injection
• Large-Volume Injection: 1000 μL direct injection onto the preconcentration column under high aqueous conditions
• Chromatography: One-minute load step, backflush onto analytical column; water and methanol both containing 0.1% formic acid; total run time 22 minutes; flow rates of 1.0 mL/min for loading and 0.4 mL/min for analysis
• Mass Spectrometry: Positive electrospray ionization at 3.0 kV; ion transfer tube at 350 °C; sheath, auxiliary, and ion sweep gases at 45, 5, and 3 arbitrary units respectively; collision gas (argon) at 1.0 mTorr; Q1/Q3 resolution set to 0.7 Da; scan width of 0.002 Da; ESI probe positioned off-axis and away from the main orifice to reduce contamination

Main Results and Discussion

• Signal Enhancement: Achieved 10 to 100-fold improvement in signal-to-noise ratios compared to standard injections, driven by large-volume loading
• System Robustness: Maintained stable column backpressure over more than 600 injections (loading column ~20 bar, analytical column ~72 bar)
• Precision: Metazachlor analysis over 164 injections yielded a relative standard deviation of 9% after initial conditioning
• Source Contamination Management: Excess matrix was directed to the drain; minor residue accumulation on the ion sweep cone did not impact performance
• Broader Applicability: Preliminary trials in onion and tobacco matrices indicated similar robustness and sensitivity

Benefits and Practical Applications

• Eliminates extensive offline sample cleanup steps, reducing hands-on time
• Delivers high-throughput capability with minimal maintenance requirements
• Supports trace-level quantitation at part-per-trillion concentrations for regulatory compliance and quality control

Future Trends and Applications

• Extension of automated online cleanup workflows to additional complex food and environmental matrices
• Integration with high-resolution mass spectrometry for non-targeted screening
• Development of portable or miniaturized systems for in-field trace analysis

Conclusion

The EQuan online sample cleanup and preconcentration system coupled with a TSQ Quantum Ultra mass spectrometer demonstrated excellent robustness, sensitivity, and reproducibility for trace pesticide analysis in challenging matrices such as red wine. The continuous performance over hundreds of injections underscores its suitability for high-throughput regulatory and research laboratories.

References

1 Wang Y, Catana F, Yang Y, Roderick R, van Breemen RB. An LC-MS Method for Analyzing Total Resveratrol in Grape Juice, Cranberry Juice, and in Wine. J Agric Food Chem. 2002;50(3):431-435.