Triolein, surface films

Figure 1.1 A standard lipid-containing SPMD with three molecular welds near each end. Note the low interfacial tension causes intimate contact (i.e., the presence of a lipid film on the membrane interior surface) between the triolein and the membrane even where air bubbles exist. Reprinted with permission from the American Petroleum Institute (Huckins et al., 2002a).

A thin film of oil-like material was visible after 28 d on the exterior surfaces of the SPMD membrane. Analysis of this film indicated that the triolein impurities, oleic acid and methyl oleate, were the major constituents. This external lipid film (Petty et al., 1993) appeared to contain imbibed particulates. Although the film was removed from the SPMDs by solvent rinsing and analyzed separately, some lipid-mediated desorption of particle-associated PCBs and subsequent diffusion into the SPMD may have occurred prior to solvent-removal of the film. This observation suggests the potential for SPMD concentrations to reflect both vapor phase concentrations and to a lesser extent, lipid-extracted particulate-associated residues (see Section 3.9.2.). Unfortunately, concentrations of more chlorinated congeners in particulates collected on GFFs from the NIOSH method were often below quantitation limits, because only a small volume of air was sampled (1 m ) using this active method. 

The first recorded observation (Adam, 13) of reaction in a monolayer, made in 1926, describes the oxidation by acid permanganate of a film of oleic acid. The reaction proceeds with expansion of the film, since the double bond in the middle of the chain is converted into a dihydroxy group, which is sufficiently hydrophilic to pull the hydrocarbon chain flat on to the surface of the water. Triolein and erucic and brassidic acids all behave in the same way. Adam also observed (14) that films of 7-hydroxy-stearolac.tone, spread on alkali, hydrolyzed to 7-hydroxystearic acid. 

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