Steven B. Dorn

Quantitative behavior of surfactants at the liquid/vacuum interface by secondary ion mass spectrometry

Abstract The behavior of a multicomponent solution of similar surfactants at the glycerol-vacuum interface as a function of bulk concentration has been studied using secondary ion mass spectrometry. Results obtained are consistent with a model which assumes simultaneous ion production, both from the surface monolayer and from the underlying bulk solution. Substantial differences in ionization efficiency among the surfactants studied were not observed. Sensitivity differences were attributable solely to differences in surface activity.

Understanding the glycerol surface as it relates to the secondary ion mass spectrometry experiment. A review

Abstract A detailed understanding of the physical processes which can occur at the glycerol surface is essential to understanding the secondary ion mass spectra obtained from glycerol solutions. Because of differences in surface activity, the relative contribution of two solutes to the surface composition can differ dramatically with profound effects on the SIMS spectrum. Both first-order and secondary effects of this type are discussed. Also discussed is the preparation of surface active derivatives, the use of surfactants of opposite charge, and the use of surfactants as reagents and complexing agents.

Study of the Degradation of Polydimethylsiloxanes on Soil

The degradation of polydimethylsiloxanes (silicones) on a spiked standard soil matrix has been studied. Spiked soil was extracted to recover silicones, and the extract was examined by several analytical techniques, including gel permeation chromatography and high-pressure liquid chromatography with an inductively coupled plasma emission spectrometer as the detector. Silicones were found to degrade rapidly to low molecular weight α,ω-siloxanediol oligomers. Within 4-6 weeks, more than half of the initial spiked silicone is converted to a water-soluble fraction consisting mostly of 1,1-dimethylsilanediol. Implications of this finding relative to the ultimate environmental fate of silicones is discussed.

The use of surfactants to modify molar response factors in the secondary ion mass spectrometry of liquid surfaces

Abstract Differences in the relative molar response observed for a series of closely related analytes in glycerol solution using secondary ion mass spectrometry are attributable largely to differences in surface activity. These differences can be minimized if a relatively large quantity of a surfactant of opposite charge is added to the solution before analysis. This added surfactant is chosen to dominate the surface selectively with the result that differences in surface activity among the species of interest become unimportant. The added surfactant does not interfere because its complementary charge state ensures very low response relative to the species of interest. It is further demonstrated that, in much the same way, surfactants can be used to enhance the response of an analyte relative to a matrix such as glycerol. This paper describes the first reported application of surfactants as reagents to modify the secondary ion mass spectra of liquid solutions.

The analysis of inorganic anions from liquid solutions using cationic surfactants and negative secondary ion mass spectrometry

Small inorganic anions such as nitrate, nitrite, iodate, bromate, cyanate, thiocyanate, chlorate, perchlorate, iodide, bromide, chloride, and tetrafluoroborate can be analyzed at low levels from glycerol solution using negative secondary ion mass spectrometry provided a long chain cationic surfactant such as tetradecyltrimethylammonium hydroxide is present in the solution. Sensitivities are directly related to the extent of association of the anion with the surface monolayer generated by the surfactant. Strongly interacting anions such as nitrate are detectable as intact ions at the 1 ng level (10−5 M in glycerol, two μl of solution). The degree of interaction between the anion and the monolayer parallels the behavior of the same ions on quaternary ammonium ion exchange resins. Fluoride and hydroxide do not interact strongly and do not give signals of useful intensity. Quantification can be readily obtained using stable isotope dilution techniques. The technique has been applied to the analysis of nitrate anion in natural precipitation.

Hydrolysis of Oligodimethylsiloxane-.alpha.,.omega.-diols and the Position of Hydrolytic Equilibrium.

The hydrolysis of tetramethyldisiloxane-1,3-diol and hexamethyltrisiloxane-1,5-diol in aqueous solutions has been studied. The position of equilibrium of the system including these compounds, dimethylsilanediol, and water has been determined. Concentrations of these compounds in dilute aqueous solutions were determined by coupling HPLC to ICP analysis for Si and also by extraction into ethyl acetate followed by triethylsilylation and GC analysis. It was found that the siloxanediols hydrolyze to the equilibrium mixture at environmentally significant rates and that dimethylsilanediol dominates the equilibrium in dilute aqueous solution, even at concentrations orders of magnitude above that expected in the environment

Levels of bioactive PCDF congeners in PCB dielectric fluids from capacitors and transformers

Abstract The levels of three pharmacologically active PCDF congeners, namely the 2,3,7,8,-tetra-, 2,3,4,7,8-penta-, and 1,2,3,7,8,9-hexachlorodibenzofurans, were measured by a precise two-dimensional gas chromatographic mass spectrometric procedure in PCB dielectric fluids taken from both used and unused capacitors and transformers, as well as in Aroclor standards. It was found that the electrical uses did not cause increases in bioactive PCDF levels.