Characterization of Diesel Particulates by Mass Spectrometry Including MS-MS

Abstract

Particles have been collected from a direct injection diesel engine at varying dilution ratios and air temperatures for four different operating conditions. Particle samples have been introduced into a mass spectrometer ion source with a direct insertion probe thus dispensing with the extraction processes typically used in chemical characterization. The sample is volatized and then chemically ionized using isobutane. Typical mass spectra are presented for each operating condition. The samples analyzed have a mean molecular weight of 195 amu with a standard deviation of approximately 100 amu. Application of tandem mass spectrometry for species identification is illustrated. Both negative and positive chemical ionization are employed to identify carboxylic acids in the particulate. Several types of ms-ms scans are shown to have utility in this study, including scans which provide molecular weight profiles for compounds having common functional groups. This latter methodology is shown to be a particularly rapid and sensitive procedure for following changes in emission characteristics in response to altered engine conditions.