Fast GC-SPI-TOF MS for On-board Monitoring of Volatile Organic Compounds in Air

Abstract

Volatile organic compounds (VOCs) are important precursors of ground-level ozone and secondary organic aerosol, and its monitoring and emission control are very necessary for national environmental protection. Under the guide of policy and demand, on-board monitoring technology for VOCs becomes popular. The on-board monitoring technology has high spatial and temporal resolution and high efficiency for VOCs monitoring, which has become the hotspot technology in VOCs rapid monitoring filed. However, when there are many target compounds with the same quality, there is only one peak in the mass spectrum for these compounds obtained by the traditional on-board monitoring technology with the method of single mass spectrometer, which reduces the detection precision. Therefore, dual mode VOCs on-board monitoring system including SPI-TOF MS model and fast GC-SPI-TOF MS model were established by developing fast gas chromatography (GC)-single photon ionization (SPI)-time of flight mass spectrometry (TOF MS) devices combing with mobile car. When VOCs were monitored by the on-board monitoring system, the SPI-TOF MS mode was firstly used to analyze the VOCs in air by the process of driving, and the results of real-time qualitative quantitative analysis for each point of VOCs were obtained. When high value point of VOCs pollution was found, the car was stopped, and the analysis mode was switched to GC-SPI-TOF MS to determine whether there were compounds with the same m/z, which aimed at ensuring the speed of onboard monitoring and improving the detection accuracy at the same time. During the research, the performance of the system was evaluated by PAMs and TO-15 standard gas. The results showed that the system had a good detection ability for isomers and co-effluent components from GC. The reproducibility error of signal intensities were lower than 5.00% for 92% compounds by both SPI-TOF MS mode and GC-SPI-TOF MS mode, the reproducibility error of retention time was lower than 0.30% for 100% compounds, and the detection limits for typical VOCs species were between 0.28×10-9 and 8.50×10-9, which were better than the national or local testing standard. The system was applied to VOCs monitoring at an industrial park. With high time resolution (in seconds) monitoring ability, m/z 120 was identified for normal propyl benzene which came from suspicious enterprises B. Rapid GC-SPI-TOF MS is a quick and accurate monitoring equipment for VOCs, which not only improves the ability of equipment for VOCs monitoring, but also provides data support for VOCs emission management and control in China.

Keywords

• fast gas chromatography
• single photon ionization-time of flight mass spectrometry (spi-tof ms)
• on-board monitoring
• volatile organic compounds