An optimised quadrupole mass spectrometer with a dual filter analyser for in-field chemical sniffing of volatile organic compounds.

Abstract

We report a novel portable 17 kg system based on a quadrupole mass spectrometer (QMS) with an electronic power consumption of 24 W. The system can be used for the in-field identification of gases and volatile/semivolatile organic compounds (VOCs/SVOCs). The mass analyser is a custom-made quadrupole mass filter with a Brubaker pre-filter that gives a mass range of m/z 1-500. It is an upgrade of the previous m/z 1-200 range triple filter analyser system. Analyser design was optimized using 3D numerical simulations as a performance trade-off between single and triple filter designs while maintaining high sensitivity and ease of integration. This also required enhanced design of the electronic control unit (ECU) compared to the previous triple filter ECU designs with lower power consumption, size, weight and cost of the overall system. Another major ECU improvement includes high stability of DC voltage control and ultra-low RF drift, which is important for in-field applications that require stable mass peaks for reliable quantitative analysis and continuous monitoring. Experimental results are presented for the perfluorotributylamine (PFTBA) calibrant and acetone to assess the functionality of the instrument. Performance comparison between the dual and triple filter quadrupole analysers has also been done. Mass spectra are given for methyl benzoate (cocaine simulant), piperidine (phencyclidine simulant), cyclohexanone (C4 simulant) and 2-nitrotoluene (TNT simulant) to assess potential capability for the identification of threat compounds. All spectral results show good correlation with the NIST library mass spectra with unit resolution obtained for spectral peaks within a m/z 1-400 mass range.