Capillary-HPLC-ESI-MS/MS method for the determination of acidic products from the oxidation of monoterpenes in atmospheric aerosol samples

A method is presented for the determination of acidic products from terpene oxidation in filter samples of the atmospheric particle phase. Oxidation products of monoterpenes are believed to add a large fraction to the secondary organic aerosol (SOA) in the troposphere. Those products with structures containing one or more carboxylic acid groups have especially low vapour pressures and therefore they are believed to contribute substantially to the particle phase. Although many experiments were performed in simulation chambers to study the SOA generation by oxidation of terpenes, concentration measurements of products in the atmospheric particle phase are still rare. This is especially true for oxidation products of terpenes other than α- and β-pinene. Therefore, we developed a method for the quantification of acidic products from terpene oxidation in atmospheric aerosol samples. After passing a PM 2.5 (PM = particulate matter) pre-separator to remove coarse particles, fine atmospheric particles were collected onto quartz fibre filters. A backup filter was placed behind the first filter to estimate possible sampling artifacts. The filters were extracted in an ultrasonic bath using methanol. After enrichment and re-dissolving in water the samples were analysed using a capillary-HPLC-ESI(−)-MSⁿ set-up. The ion trap mass spectrometer could be used to gain structural information about the analytes and to enhance the selectivity of the measurements by using its MS/MS capability. A variety of products from different terpenes could be identified and quantified in samples of the ambient atmosphere using reference data from chamber experiments. Due to strong matrix effects quantification of samples from the real atmosphere had to be done by the standard addition method.