Free amino acids in atmospheric particulate matter of Venice, Italy

The concentrations of free amino acids were determined in atmospheric particulate matter from the city of Venice (Italy) in order to better understand their origin. The analysis of aerosol samples was carried out via high-performance liquid chromatography coupled to a triple quadrupole tandem mass spectrometric detector (HPLC/ESI-MS/MS). The internal standard method was used and the analytical procedure was validated by evaluating the trueness, the precision, the recovery, the detection and the quantification limits.The particulate matter was collected using quartz fiber filters and extracted in methanol; after filtration the extract was directly analyzed. Forty samples were collected from April to October 2007 and the average concentrations of free amino acids in the aerosol were: alanine 35.6pmolm -3, aspartic acid 31.1pmolm -3, glycine 30.1pmolm -3, glutamic acid 32.5pmolm -3, isoleucine 2.4pmolm -3, leucine 2.7pmolm -3, methionine, cystine and 3-hydroxy-proline below the limit of detection, phenylalanine 2.8pmolm -3, proline 43.3pmolm -3, serine 8.6pmolm -3, threonine 2.8pmolm -3, tyrosine 1.7pmolm -3, valine 3.8pmolm -3, asparagine 70.2pmolm -3, glutamine 38.0pmolm -3, 4-hydroxy-proline 2.5pmolm -3, methionine sulfoxide 1.1pmolm -3, and methionine sulfone 0.1pmolm -3. The total average concentration of these free amino acids in aerosol samples of Venice Lagoon was 334pmolm -3. The temporal evolution and multivariate analysis indicated the photochemical origin of 4-hydroxy-proline and methionine sulfoxide and for other compounds an origin further away from the site of sampling, presumably reflecting transport from terrestrial sources.