Development and Characterization of an Aerosol Time-of-Flight Mass Spectrometer with Increased Detection Efficiency

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• 作者：Yongxuan Su ; Michele F. Sipin ; Hiroshi Furutani ; and Kimberly A. Prather
• 刊名：Analytical Chemistry
• 出版年：2004
• 出版时间：February 1, 2004
• 年：2004
• 卷：76
• 期：3
• 页码：712 - 719
• 全文大小：127K
• 年卷期：v.76,no.3(February 1, 2004)
• ISSN：1520-6882

文摘

This paper describes the development and characterization studies of a more efficient aerosol time-of-flight massspectrometer (ATOFMS), showing results for the on-linedetection and determination of the size and chemicalcomposition of single fine (100-300 nm) and ultrafine(<100 nm) particles. An aerodynamic lens inlet wasimplemented, replacing the converging nozzle inlet usedon conventional ATOFMS instruments. In addition, thelight scattering region was modified to enhance thescattering signals for smaller particles. Polystyrene latexspheres (PSL) with aerodynamic diameters ranging from95 to 290 nm were used to characterize the particle sizingefficiency (product of particle transmission efficiency andparticle scattering efficiency), particle detection efficiency(product of particle sizing efficiency and particle hit rate),and particle beam profile and perform instrument calibration. At number concentrations of <20 particles/cm³, theparticle sizing efficiencies were determined to be ~0.5%for 95 nm and ~47% for 290-nm PSL particles, while theparticle detection efficiencies were measured to be ~0.3%for 95 nm and 44% for 290-nm PSL particles. Thisrepresents a significant increase (i.e., at least 3 orders ofmagnitude) in detection efficiencies for smaller particlesover the conventional ATOFMS. In addition, the beamprofiles for PSL particles of various sizes were measuredin the ion source of the mass spectrometer and follow aGaussian distribution with a full width at half-maximumof ~0.35 mm. The resulting higher detection efficienciesallow ATOFMS to obtain higher temporal resolutionmeasurements of the composition of fine and ultrafineindividual particles as demonstrated in initial ambientmeasurements in La Jolla, CA. At typical ambient particlenumber concentrations of 10²-10³ particles/cm³,~30 000 particles with aerodynamic diameters of <300nm were detected with average 24-h hit rates of 30% forparticles between 50 and 300 nm. This advancement,allowing for high temporal resolution measurements ofthe composition of smaller particles with higher efficiency,adds to a growing number of instruments that can chemically characterize individual fine and ultrafine particles,with the goal of providing new insights into a number ofareas including environmental and material sciences,health effects studies, industrial hygiene, and nationalsecurity.