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AMT12 aerosol amino acid analysis

Originator's Protocol for Data Acquisition and Analysis

Atmospheric sampling was conducted on the JCR's monkey island when wind conditions permitted, i.e. apparent wind direction was forward of the monkey island ensuring no contamination from the ship's stacks. Samplers were in general turned off while on station unless the bridge were confident of remaining head to wind throughout all manoeuvring. Sampling throughout passage allowed 16-20 hours sampling per day. A high volume aerosol sampler (approx. 0.8 m ³ min ^-1 ) was deployed for trace organic analysis and used pre-ashed glass fibre filters. Filters containing atmospheric aerosol were stored at -20 ^o C in pre-combusted aluminium foil envelopes, placed in seperate palstic bags. Clean handling procedures were observed throughout with the filter holder being loaded and unloaded in a laminar flow cabinet. Blank samples were also collected using the same protocol but without turning on the airpump (Wedyan and Preston, 2008).

The amino acids in the aerosols were seperated into three fractions (i) the dissolved free amino acids (DFAA) (i.e. those uncombined amino acids directly extractable into water), (ii) the dissolved hydrolysable amino acids (DHAA) (i.e. those combined amino acids directly extractable into water and released by hydrolysis), (iii) the particulate amino acids (PAA) (i.e. those not extractable from the filter into water but liberated by hydrolysis). Hydrolysis was carried out with 900 µL of sample pipetted into a clean Pyrex culture tube with 100 µL of internal standard (L-homarginine) and then 1 mL of 50% hydrochloric acid solution. Nitrogen was bubbled through the sample for 1 minute prior to sealing with a Teflon-faced screw-top lid to prevent oxidation of the amino acids. The tubes were then hydrolysed at 110 ^o C for 6 hours and subsequently freeze-dried. The samples were then re-dissolved in a minimum amount of Milli-Q water (Wedyan and Preston, 2008). The amino acids were separated by HPLC using a reversed phase column and the modified solvent programme from Kaufman and Manley (1998)

References Cited

Kaufman D. and Manley W., 1998. A new procedure for determining DL amino acid ratio in fossils using reverse liquid chromatography. Quaternary Geochronology, 17, 987-1000.

Wedyan M.A. and Preston M.R., 2008. The coupling of surface seawater organis nitrogen and the marine aerosol as inferred from the enantiomer-specific amino acid analysis. Atmospheric Environment, 42, 8698-8705.

Instrumentation Description

Not relevant to this data set.

BODC Data Processing Procedures

Data were submitted in an Excel spreadsheet with the following metadata; Sampling start and end date and time, Latitude and Longitude. The sampling data were loaded to the database and the date and times provided converted from local time to UT. The positional data were verified using the data from the navigational channels in the underway file. The data were assigned parameter codes defined in BODC parameter dictionary. Data were loaded into BODC's database using established BODC data banking procedures, and units were converted from nmol m ^-3 to pmol m ^-3 using a conversion factor of x1000.

A parameter mapping table is provided below;

Data Quality Report

BODC were not advised of specific quality checks carried out by the data originators. There were no standout values in the sample data provided to BODC.

Problem Report

Not relevant to this data set.