Rapid ppb-Level Methane Detection Based on Quartz-Enhanced Photoacoustic Spectroscopy

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Environmental Science

Background:

• Methane (CH4) detection is crucial for environmental monitoring and industrial safety.
• Traditional QEPAS systems face limitations in sensitivity and detection speed.
• Developing advanced sensors for accurate and rapid CH4 analysis is essential.

Purpose of the Study:

• To report the first-time implementation of quartz-enhanced photoacoustic spectroscopy (QEPAS) and heterodyne QEPAS (H-QEPAS) for ppb-level methane detection.
• To utilize a novel low-frequency round-head quartz tuning fork (QTF) and a power-amplified diode laser for enhanced performance.
• To demonstrate the practical application of the developed sensor for continuous CH4 monitoring.

Main Methods:

• Employed a self-designed 9.7 kHz round-head QTF as an acoustic wave transducer.
• Utilized a Raman fiber amplifier (RFA) to boost diode laser power to 300 mW.
• Integrated acoustic microresonators (AmRs) to amplify acoustic waves, achieving a 107-fold signal enhancement.

Main Results:

• Achieved ppb-level detection limits for CH4: 1.321 ppb (QEPAS) and 2.126 ppb (H-QEPAS) with 1000 s integration time.
• Demonstrated excellent linearity (R-squared > 0.99) for both sensor configurations.
• H-QEPAS achieved rapid measurements in 3 s with real-time QTF resonance frequency calibration.

Conclusions:

• The novel QTF and AmR integration significantly enhances QEPAS performance for CH4 detection.
• The developed CH4-QEPAS and CH4-H-QEPAS sensors offer high sensitivity, linearity, and rapid measurement capabilities.
• The system is suitable for continuous monitoring of CH4 in ambient air and biological samples.