Combined amino acids (CAA) were quantified in 7 aerosol samples collected during the Arctic campaign at Gruvebadet Laboratory in 2015. Combined amino acids (CAA) refer to amino acids contained in peptides, polipeptides and proteins.Aerosol samples were collected in quartz fiber filters. They were spiked with isotopically labelled standard solutions (2 - 3 µg/ml) prior extraction. CAA content was measured using HPLC-MS.

For the analysis of CAAs, in a 1.5 mL vial, 500 mL of each sample extract was mixed with 500 mL of 12M HCl and 5 mL of ascorbic acid at a concentration of 1 ng/mL to avoid oxidation of the amino acids. The vial was flushed with a stream of nitrogen before sealing and placed in a heat-block at 110 °C for 24 h with a Liebig prototype glass condenser used to condense compounds in the vapor (gas) phase back down to the liquid phase under boiling conditions through heat exchange with the environment. The hydrolysis products were freeze-dried to eliminate traces of HCl. The dry residues were subsequently dissolved in 500 mL of ultrapure water and diluted 1:10 before analysis for total amino acids (TAAs). The extracts of the field blank filters were also hydrolyzed so all TAAs concentrations could be blank corrected. The concentrations of the CAAs were calculated as the difference between the TAAs and free amino acids (FAAs) concentrations.Values below the detection limit of the measurements are indicated (<0.xxxxx).