Analytica Chimica Acta (1987) 198: 125-144.
Received: 29 September 1986.
A procedure is described for the determination of organic compounds in aerosols and rain from the remote marine atmosphere. Five classes of naturally occurring lipids (n-alkanes, wax esters, fatty alcohols, sterols and fatty acids) were quantified in the samples. Air samples (4000-10,000 m³) were collected on glass-fiber filters under automatic control. Rain samples (1-5 L) were collected on an event basis. Filter and rain samples were extracted with dichloromethane and the extracts were fractionated into discrete chemical classes by adsorption chromatography with silica gel. The fractions were derivatized (if necessary) and quantified by high-resolution glass-capillary gas chromatography (HRGC) and HRGC-mass spectrometry (HRGC-MS). A second filter extraction was required for quantification of fatty acid salts. On-column injection of the fractions provided identification and quantification of a wide range of homologs within each compound class: C15-C44 for n-alkanes, C39-C62 for wax esters, and C13-C36 for fatty alcohols and fatty acids. Internal standards were used to quantify recoveries and concentrations. Mean recoveries relative to the internal standards were 96.5% for C18-C36 n-alkanes, 96.4% for C20-C30 n-fatty acids, 92.5% for C14-C30 n-fatty alcohols and 93.3% for cholesterol. The procedural blanks for the remote marine aerosol samples allow detection limits of 0.1-1.0 pg/m³ for most compounds. These values are lower than any other method used at coastal marine, rural or suburban sampling locations.
We thank Dr. Oliver Zafiriou for helping us to formulate the method; Ms. Gale Nigrelli and Dr. Stuart Wakeham for their comments and direction during the development of the silica gel and gas chromatography procedure; and Dr. Nelson M. Frew's assistance with the gas chromatography-mass spectrometric analyses. We thank Ms. Jane Alford for her work in the laboratory processing most of the Enewetak and American Samoa aerosol and rain samples. We are grateful to Mr. C. Snipes and W. Koga at Holmes and Narver, Inc., the staff of the University of Hawaii's Mid-Pacific Marine Laboratory at Enewetak Atoll, the Department of Energy, and Mr. Don Nelson and the staff at the National Oceanic and Atmospheric Administration, Global Monitoring for Climatic Change Observatory in American Samoa for major logistical support during the field work at these sites. This work was supported by the National Science Foundation, Ocean Sciences Division under NSF grants OCE 77-12914, OCE 81-11947 and OCE 84-06666 as part of the SEAREX program.