Classification of HULIS carbon from different atmospheric environments via a 2-D-Off-line chromatography
Final Report Abstract
Within the DFG project HuCar, the composition and variability of HULIS in atmospheric aerosol particles from different sampling sites and seasons was studied. To this end, a 2D-LC fractionation method combining SEC and RP-HPLC was developed. The particle extracts were separated via optimized SEC into five fractions in molar mass ranges between 160-900 g/mol. Each fraction was separated further into eleven RP-HPLC fractions with calculated octanol/water partition coefficients of 0.2-3.3, utilizing a newly developed “spiked gradient” method. Heat maps of the UV- absorption at 254 nm illustrate the distribution of HULIS in the two-dimensional sizevs-polarity space. With this method, clear differences is the composition of HULIS were detectable and further analyzed with distance matrix computation and cluster analysis. The composition of HULIS is strongly influenced by the sampling site as well as the sampling season. Filter samples from Melpitz collected in the winter differed strongly from filter samples collected during the summer. Further, samples collected near Beijing in the summer, showed more similarities to samples from Melpitz collated in the winter, than in the summer. However, they still composed their own cluster in the respective analysis. Sample collected in Italy during the PEGASOS-campaign (Summer 2012) also composed their own cluster, with higher similarity to Melpitz summer samples. To further analyze the chemical composition of HULIS, the individual fractions of one sample were analyzed by ESI-FT-ICR MS. The number of identified, unique molecular formulas increased by a factor of ~2.3 for the fractionated samples as compared to bulk (non-fractionated) sample, likely due to a reduction of ion suppression in ESI and hence sensitivity enhancement of low concentration HULIS compounds. The estimate of the number of compounds (71240) increased by a factor of 9.1 compared to the bulk sample due to the chromatographic separation of isomers into different sample fractions. The most important compound classes identified in the fractionated sample were organo- and poly-organonitrates, organosulfates and nitrooxy-organosulfates, but also amine-like compounds and polyaromatic compounds were found as important particle constituents.
