Chemistry Reference
In-Depth Information
surface-active compounds spanning a wide range of polarity, molecular
weight and chemical structure (Frew and Nelson 1992a,b). As multicom-
ponent systems, microlayer films exhibit a more complex rheological re-
sponse to surface straining than monolayers of single pure compounds
(Bock and Frew 1993, Krägel et al.1995, Kozarac et al. 2000).
This paper discusses studies of sea surface films observed and collected
in the southern California Bight and the U. S. Middle Atlantic Bight. The
goals of these studies were to understand the relationship between chemi-
cal composition and surface elasticity in these complex natural films and to
determine the range of surface elasticity typical of the ocean surface. Mass
spectrometry was the principal analytical tool because of its capacity to
characterise and identify chemical structures for many compound classes
and to provide a quick assessment of compounds enriched in sea surface
films. We present typical variations in SAOM chemical composition as re-
flected in mass spectral patterns and show the effect of these compositional
variations on the film elasticity.
2. Methodology
2.1. Microlayer Sampling and Extraction
The sea surface microlayer was sampled with a surface skimmer of a de-
sign similar to that of Carlson et al. (1988). The sampler consisted of a par-
tially submerged, rotating glass cylinder supported by a small catamaran.
The rotating cylinder collected a thin layer of water (40-60 Pm thickness)
by viscous retention. The theoretical basis for the sampling mechanism
was described by Levich (1962) and verified experimentally by Cinbis
(1992). The sampler was used to collect large volume (20 L) samples of
the microlayer and subsurface water (10 cm nominal depth). The SAOM
was extracted from microlayer and bulk seawater samples using bubble
adsorption in a foam tower apparatus (Wallace et al. 1972). Briefly, sam-
ples were filtered through pre-combusted Whatman glass fiber filters
(GF/F 1 Pm nominal pore size) under low nitrogen pressure to remove par-
ticulate matter and organisms; 6.5 L of the filtered samples were then
loaded into the foam tower. A plume of ultrahigh purity nitrogen bubbles
generated by a frit in the tower base was used to adsorb and strip surfac-
tants from the large volume samples, producing a surfactant-enriched foam
that was collected at the top of the apparatus. The concentrated SAOM in
the foam was then fractionated by extraction into a series of increasingly
polar solvents to provide three SAOM fractions designated F1 (1:1
n
-hex-
ane/dichloromethane), F2 (2:1 trichloromethane/methanol) and F3 (10:9:1
