Determination of polar terpene oxidation products in aerosols by liquid chromatography-ion trap mass spectrometry

A new method for the determination of polar terpene oxidation products in secondary aerosols is described. It is based on collection of particles on PTFE filters and extraction with dichloromethane followed by analysis with liquid chromatography-ion-trap mass spectrometry (MSn) using pneumatically assisted electrospray ionisation (ESI) and atmospheric pressure chemical ionisation (APCI) with the ion-trap operated in the product scan mode. Separations were achieved on a C-18 reversed-phase column with methanol-water (0.1% acetic acid) as eluent. The method has a high sensitivity (instrument detection limit 0.7-7 pg/mu l at S/N=3) and precision (5-10%) and a good linearity. Acidic oxidation products produce strong signals with ESI, They appear as negative quasimolecular ions [M-H](-), acetate adducts [M+CH3COO](-) and molecular clusters [2M-H](-). In the MS2 mode these acids show strong signals from neutral loss of CO2: [M-H-CO2](-), and/or weaker signals from loss of H2O: [M-H-H2O](-), [M-H-H2O-CO2](-). Mass spectra were recorded by APCI for a number of oxygenated terpenoid standards containing keto groups, hydroxy groups, aldehyde groups, or epoxy groups. These compounds give intense signals as their positive quasimolecular ions [M+H](+), methanol adducts [M+H+CH3OH](+) and fragments from loss of water, such as [M+H-H2O](+), [M+H+CH3OH-H2O](+) and [M+H-2H(2)O](+). By MS2 and MS3 neutral loss of H2O and 2H(2)O is observed. The method has been tested in analysis of aerosol from O-3-alpha-pinene and O-3-myrtenol and has been proved to compare well with classical methods based on derivatisation and gas chromatography mass spectrometry. Three new compounds, tentatively identified in aerosol are reported here for the first time: 10-hydroxypinonic acid, 9-hydroxynorpinonic acid and pinalic 4-acid. (C) 1999 Elsevier Science B.V. All rights reserved.